CF₃-pyridyl-substituted hetero- and homocyclic conjugated molecules: from non-emissive to highly emissive through core engineering

Abstract

Herein, we report the synthesis of six CF₃-pyridyl-substituted aromatics via Suzuki–Miyaura cross-coupling, incorporating electronically diverse heterocyclic (pyrazine and benzothiadiazole) and homocyclic (chrysene, anthracene, pyrene, and perylene) cores to systematically probe structure–property relationships. UV-vis absorption, steady-state and time-resolved photoluminescence, electrochemical measurements, and quantum chemical calculations demonstrate that the homocyclic derivatives exhibit long fluorescence lifetimes (τ), high photoluminescence quantum yields (Φ_PL), large dipole moment changes (Δµ), optimally aligned frontier energy levels, and backbone-delocalized charge redistribution. Among these, the anthracene-based compound (H-An) shows the longest τ and highest Φ_PL with strongly suppressed non-radiative decay, the pyrene derivative (H-Py) displays the largest Δµ, while the perylene analogue (H-Per) demonstrates red-shifted absorption, computed high light-harvesting efficiency, minimal exciton binding energy, and the lowest hole and electron reorganization energies, highlighting their potential as bright emitters or absorbers for optoelectronic applications. In contrast, the heterocyclic compounds (H-Pz and H-BTD) are weakly emissive or nearly non-emissive, indicative of dominant non-radiative relaxation pathways. Density functional and time-dependent DFT calculations reproduce the experimental trends, underscoring that strategic core engineering within the CF₃-pyridyl framework is an effective approach for tuning optical, charge transport, and emissive properties in organic optoelectronic materials.

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Introduction

Strategic molecular design of π-conjugated molecules is central to advancing organic optoelectronic devices such as organic solar cells (OSCs), organic field effect transistors (OFETs), perovskite solar cells (PSCs), sensors, and organic light emitting diodes (OLEDs).^1,2 Careful selection of central π-cores, terminal groups, and attached substituents allows precise tuning of frontier molecular orbitals (FMOs), molecular packing, charge transport, and photophysical properties.^3,4 To achieve state-of-the-art organic functional materials, researchers have explored a variety of π-cores, including electron deficient heterocycles such as pyrazine⁵ and benzothiadiazole⁶ for their strong acceptor nature, and rigid homocycles such as chrysene,⁷ anthracene,⁸ pyrene,⁹ and perylene¹⁰ for their extended conjugation and excellent photo and thermal stability, embedding them with unique terminal groups such as pyridine,¹¹ quinoline,¹² and triarylamine.^13,14 For example, in 2020, Marder's group investigated nine regioisomeric dipyridyl-pyrene derivatives and demonstrated the strong dependence of their photophysical properties on molecular design.¹⁵ Similarly, Kido's group reported a terpyridine- modified chrysene derivative as an efficient electron transport layer (ETL) in ultra-stable phosphorescent OLEDs, attributing its performance to planarity induced by the terpyridine moieties.¹⁶ In 2023, Ren's group theoretically investigated the charge transport properties of 2,6-dipyridyl anthracene isomers and revealed superior charge transport for the meta isomer compared to the excellent 2,6-diphenyl anthracene molecule, mainly due to favourable intermolecular interactions (Fig. 1).¹⁷

Fig. 1 Selected examples of trifluoromethylated and pyridyl-substituted conjugated molecules reported in the literature.

Despite such progress, fluorination remains one of the most powerful strategies for achieving the desired optoelectronic properties.¹⁸ Trifluoromethylated (–CF₃) compounds have been extensively used in fields ranging from pharmaceuticals to optoelectronic materials owing to their strong electron withdrawing effect and high electronegativity (3.5 on the Pauling scale).¹⁹ Such remarkable features enable the –CF₃ group to lower FMO energy, improve optical properties, and facilitate non-covalent interactions (NCI) such as C–F⋯H, C–F⋯S, and C–F⋯π, ultimately influencing molecular packing, planarity, stability, and device performance.^20,21 To exploit these advantages, researchers have widely incorporated –CF₃ substituents into π-conjugated scaffolds. For instance, Kaafarani's group synthesized nine 1,3,6,8-tetraarylpyrene derivatives, with selected candidates tested for OLEDs, and found that the 3,5-bis-CF₃-substituted compound exhibited the highest absolute quantum yield (Φ_PL = 0.918) in the crystalline state due to enhanced intermolecular interactions facilitated by CF₃ groups.²² Similarly, Kim's group synthesized an anthracene-based molecule featuring naphthalene units at the 9,10-positions and 3,5-bis(trifluoromethyl)phenyl units at the 2,3-positions; this compound demonstrated high thermal stability (5% weight loss at ∼398 °C), stabilized FMOs, and high quantum efficiency resulting from CF₃-induced molecular twisting compared to CF₃-substituted analogues.²³ Additionally, Soulé's group reported Pd-catalyzed C–H bond arylation of 2,1,3-benzothia/selenadiazole derivatives and observed that among 4,7-diaryl-2,1,3-benzothiadiazoles, the 3,5-bis(trifluoromethyl)phenyl substituted analogue displayed the highest quantum yield (Φ_PL = 0.89) in thin films and significantly better properties than non-fluorinated derivatives (Fig. 1).²⁴

Although numerous reports describe –CF₃ group substituted or pyridyl-substituted π-conjugated systems, CF₃-substituted pyridyl bearing small π-conjugated molecules remains underexplored. To the best of our knowledge, no systematic study has examined how incorporating CF₃-pyridyl terminal groups across electronically diverse π-cores ranging from electron-deficient heterocycles to electron-rich polyaromatics influences their electronic and photophysical behaviour. In our previous work, we reported the Ir-catalyzed C–H borylation of 2,6 bis(trifluoromethyl)pyridine in 2017,²⁵ which we later extended in 2022 to access 26 new CF₃-pyridyl boronic esters.²⁶ Building on this foundation and addressing this literature gap, we sought to investigate the structure–property relationships of CF₃-pyridyl-substituted π-conjugated molecules and to understand the role of core engineering in modulating their photophysical, electrochemical, charge transport and emissive properties.

In this context, we report the design and synthesis of six new 2,6-bis(trifluoromethyl)pyridyl-substituted π-conjugated molecules incorporating pyrazine, benzothiadiazole, chrysene, anthracene, pyrene, and perylene as central cores. These cores were selected for their contrasting electronic nature (electron-deficient vs. electron-rich) and structural diversity (heteroaromatics vs. (homo)polyaromatics), enabling a comparative investigation of their structure–property relationships. This study involves the photophysical, cyclic voltammetric, and computational studies of all target compounds.

Methodology

The synthesis of all the target compound was carried out in two steps as outlined in Scheme 1. Firstly, we carried out the Ir-catalyzed C–H activation of 2,6-bis(trifluoromethyl)pyridine to access compound A according to a protocol reported by Chotana's group.²⁵ Subsequently, compound A was subjected to Suzuki–Miyaura cross-coupling reaction with six dibromo-substituted π-aromatic cores to afford the target compounds (H-Y). All the target compounds were purified by column chromatography and obtained in good to excellent yields (61–92%). Finally, all compounds were characterized by FT-IR, GC–MS, and NMR spectroscopy (Experimental Section and Fig. S15–S37).

Scheme 1 Synthesis of all the target compounds reported in this study.

Photophysical properties

The comprehensive photophysical studies were carried out in solutions by using ten different solvents of varying polarity, including nonpolar, polar aprotic, and polar protic with distinct dielectric constants and refractive indices. The absorption and emission spectra are given in Fig. 2 and Fig. S1, S2, and the corresponding data are outlined in Table 1 and Table S1. In Fig. 2A, all compounds display two main absorption bands. The high-energy band in the 248–281 nm region is assigned to localized π → π* transitions mainly associated with the CF₃-pyridyl terminal unit, while the broad low-energy band in the 309–461 nm region is attributed to mixed π → π*/ICT transitions involving the central core and the terminal pyridyl acceptor. The CF₃-pyridyl unit acts as a strong electron-withdrawing acceptor due to the combined –I effect of the CF₃ group and the electron-deficient pyridyl ring.²⁷ This leads to stabilization of the LUMO and provides the driving force for charge transfer from the central core toward the terminal units. This interpretation is consistent with related pyridyl based conjugated systems reported in the literature, where the higher-energy band corresponds to localized excitation and the lower-energy band charge transfer character.^27–29 TD-DFT results (Tables S11–S22) further support this, showing that the low-energy transition is dominated by HOMO → LUMO excitation with strong charge redistribution from the core toward the CF₃-pyridyl terminal rings. Conversely, higher-energy transitions involve multiple contributions from deeper occupied orbitals and higher unoccupied orbitals, confirming their localized π → π* character.

Fig. 2 Photophysical properties of all compounds. (A) UV-vis absorption spectra recorded in CHCl₃ solution (conc. = 10⁻⁴–10⁻⁵ M). (B) Emission spectra recorded in CHCl₃ solution conc. = 10⁻⁴–10⁻⁵ M) and excitation wavelengths in the window of 20 nm lower and higher with respect to λ_max. (C) Fitted slope comparison calculated from Lippert–Mataga analysis. (D) Normalized fluorescence lifetime decay plots recorded in CHCl₃ (Excitation wavelengths for H-Pz (374 nm), H-BTD (550 nm), H-Ch (566 nm), H-An (545 nm), H-Py (472 nm), H-Per (650 nm) and bandwidth (10 nm).

Table 1 Optical data for all compounds recorded in CHCl₃, where λ_abs = absorbance wavelength maxima, λ_em = emission wavelength maxima, E_0–0 = optical band gap (eV) =1240/(λ_max(nm), Stokes shift = Δν (cm⁻¹), dipole moment change = Δµ (D), photoluminescence quantum yield = Φ_PL and radiative and non-radiative constants = k_r, k_nr

Compd	λabs (nm)	λem (nm)	E0–0 (eV)	Δν (cm^−1)	Δµ (D)	ΦPL (%)	τ (ns)	kr 10^8 (s^−1)	knr 10^8 (s^−1)
H-Pz	256, 309	396	4.01	7109.9	—	—	0.060	—	—
H-BTD	279, 351	422	3.53	4793.4	—	7.6	2.088	0.37	4.42
H-Ch	264, 344	419	3.60	5203.4	10.30	72.3	2.378	3.04	1.16
H-An	248, 394	457	3.15	3498.9	10.88	94.6	6.212	1.52	0.09
H-Py	281, 368	442	3.37	4549.5	18.11	90.4	2.839	3.18	0.34
H-Per	256, 461	544	2.69	3309.6	11.87	86.9	2.839	3.06	0.46

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Overall, the absorption trend follows H-Per > H-An > H-Py > H-BTD > H-Ch > H-Pz. This trend is quantitatively supported by the HOMO–LUMO energy gaps obtained from electrochemical and computational analyses. The band gaps decrease systematically from H-Pz (4.01 eV) and H-BTD (3.53 eV) to H-Per (2.69 eV), indicating that extended π-conjugation in homocyclic cores effectively narrows the energy gap and facilitates lower-energy electronic transitions. A similar trend is observed in the computed energy gaps, further validating the experimental observations. Additionally, frontier molecular orbital distributions show that in homocyclic derivatives the HOMO is largely delocalized over the central aromatic core, while the LUMO extends toward the CF₃-pyridyl terminals, enabling more efficient intramolecular charge transfer. In contrast, heterocyclic systems exhibit relatively localized orbital distributions, which limits effective conjugation and results in higher-energy absorption bands.

On the other hand, the emission spectra (Fig. 2B) show broad fluorescence bands in the 396–544 nm range, and the emission maxima follow the same trend, H-Per > H-An > H-Py > H-Ch ≈ H-BTD > H-Pz.

To comprehend the solvent effect on the photophysical properties of the designed molecules, we carried out the Lippert–Mataga analysis.³⁰ This model treats the solute as a point dipole in a spherical cavity within a dielectric continuum and does not account for specific solute–solvent interactions such as hydrogen bonding, π–π stacking, aggregation, or charge transfer complex formation.^31–33 The absorption spectra show only minor changes with solvent polarity, indicating that the ground state is only weakly perturbed by the medium. This observation is consistent with the very small ground-state dipole moments (µ_g) predicted by DFT (0.0001–0.7786 D, Table S4). These low values are not computational artifacts but arise from the near-symmetric molecular architectures, where the individual dipole vectors of the CF₃-pyridyl units cancel each other. To verify this, we optimized homocyclic derivatives against four hybrid DFT functionals (B3LYP, CAM-B3LYP, MPW1PW91, and WB97XD, Table S3). All DFT functionals gave consistently low µ_g values, confirming that the small dipoles (µ_g) are intrinsic to their molecular symmetry.

In contrast, the emission spectra show pronounced solvatochromic shifts. For the homocyclic compounds, Stokes shift versus orientation polarizability (Δf) gives well-defined linear correlations with positive slopes, supporting a normal Lippert–Mataga response. The heterocyclic compounds H-Pz and H-BTD deviate from this behaviour and give negative slopes, indicating that the simple continuum model is not adequate for these compounds (Fig. 2C and Fig. S3). These deviations likely arise from specific solute–solvent interactions and excited-state stabilization, especially through heteroatom-solvent interactions, which are not captured by the Lippert–Mataga model. To further examine these effects, we carried out multi-parameter Kamlet–Taft analysis, which accounts for solvent polarity (π*), hydrogen-bond donor ability (α), and hydrogen-bond acceptor ability (β) (Figure S5).³⁴ For H-Pz, the strong dependence on solvent basicity (β) suggests specific hydrogen-bonding interactions between solvent molecules and the pyridine/pyrazine nitrogen atoms, which stabilize the excited state. For H-BTD, the poor regression fit indicates a more complex solvent response, likely influenced by the sulfur-containing core. Thus, in our hands, the Lippert–Mataga model works well for the homocyclic cores but shows limitations for the heterocyclic derivatives due to dominant specific solute–solvent interactions.

For the homocyclic derivatives, excited-state dipole moments (µ_e) were calculated using ground-state dipole moments (µ_g) and Onsager radii (a) obtained from DFT-optimized geometries (Table S4), following the methodology reported by Wee's group.³⁵ The calculated Δµ values follow the order H-Py > H-Per > H-An > H-Ch, consistent with the relative steepness of the Lippert–Mataga slopes. The large µ_e (10.30–18.11 D) clearly indicates substantial charge redistribution upon photoexcitation, confirming efficient charge transfer across these molecules.³⁶ This is further supported by the natural population analysis (NPA) (Fig. S38), where the charge distribution is clearly shifted toward CF₃-pyridyl units. The homocyclic systems show larger core-to-terminal charge separation than the heterocyclic analogues, with the NPA values decreasing in the order H-Per (+0.08846) > H-Py (+0.08237) > H-Ch (+0.07578) > H-An (+0.05829) > H-Pz (+0.03188) > H-BTD (+0.02474). This clearly shows that the homocyclic derivatives possess stronger ICT character, while the heterocyclic compounds exhibit weaker charge redistribution.

Fluorescence lifetimes (τ) and photoluminescence quantum yields (Φ_PL) were measured in chloroform, and the radiative (k_r) and non-radiative (k_nr) decay constants were calculated from the Φ_PL and τ (Table 1, Fig. 2D, and Fig. S4, S8–S12). All compounds exhibit predominantly single-exponential decay profiles, indicating the presence of a single emissive excited state. Compounds containing homocyclic aromatic cores show significantly higher Φ_PL values (72.3–94.6%) and longer lifetimes (2.378–6.212 ns) compared to heterocyclic analogues. This behaviour can be attributed to the rigid, planar, and π-extended nature of the homocyclic frameworks, which suppress vibrational relaxation and favour radiative decay pathways.^15,37 Correspondingly, these compounds exhibit relatively high k_r in the range of ∼1–3 × 10⁸ s⁻¹.

Interestingly, among all compounds, H-An exceptionally demonstrated the highest Φ_PL of 94.6% with a τ of 6.212 ns with the lowest k_nr, because of its linear three acene ring geometry, which promotes efficient π-delocalization while minimizing non-radiative deactivation pathways such as internal conversion and intersystem crossing.³⁸ In contrast, H-BTD has shown the lowest Φ_PL of 7.6% mainly because of the presence of heteroatoms like S in the central core. This quenching may be attributed to fast non-radiative decay, likely via enhanced intersystem crossing (sulfur-mediated SOC) and/or rapid relaxation to a non-emissive CT minimum, which is further supported by problematic Lippert–Mataga slopes and the divergence between TDDFT oscillator strength and observed emissive efficiency.^39,40

Electrochemical properties

The electrochemical behaviour of the compounds was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in anhydrous DCM using 0.1 M Bu₄NPF₆ as the supporting electrolyte in a three-electrode setup, i.e., glassy carbon as the working electrode, Pt wire as the counter electrode, and Ag/AgCl as the reference electrode. Ferrocene was measured as an internal standard under identical conditions, and its oxidation potential was determined to be 0.26 V (Fig. S14a). Oxidation potentials (E⁰_Oxi) for all compounds were determined from the oxidation peak potentials obtained from Differential Pulse Voltammetry (DPV, Fig. 3) and supported by cyclic voltammetry (CV, Fig. S13) and all values are referenced directly to Fc/Fc⁺.

Fig. 3 Differential pulse voltammetric (DPV) traces for all compounds acquired in 0.1 M Bu₄NPF₆ as a supporting electrolyte in anhydrous DCM solvent at a 100 mV s⁻¹ scan rate and potential window potential (−2 to 2 V).

In Fig. 3, heterocyclic compounds H-Pz and H-BTD exhibit two well-defined reduction peaks (for H-Pz: −1.20 V and −1.60 V; for H-BTD: −1.09 V and −1.42 V) in the cathodic region, indicating sequential one-electron reduction processes from the neutral molecule to the radical anion and then to the dianion. This behaviour arises from the electron-deficient nature of the central cores (Pz and BTD), which stabilise the added electrons.^41–43 The frontier molecular orbital (FMOs) analysis (Fig. 5A) shows that the LUMO and LUMO+1 are primarily localized on the electron-deficient central core, supporting the stepwise electron uptake and stabilization of the reduced species. In contrast, the homocyclic analogues generally show a single reduction peak, indicating that further reduction is less favourable under the same conditions. This can be attributed to their extended central cores, which result in a different spatial distribution of the LUMO and LUMO+1 orbitals. Specifically, in these molecules, the LUMO is primarily localized on the central core, while the LUMO+1 is shifted towards the terminal CF₃-pyridyl rings with increased energy, thereby limiting additional electron accommodation (Table 2).

Table 2 Electrochemical data

Compd	E^0Oxi (V)	HOMO^a (eV)	LUMO^a (eV)	Eg^a (eV)	HOMO^b (eV)	LUMO^b (eV)	Eg^b (eV)
H-Pz	1.62	−6.29	−2.28	4.01	−7.74	−3.34	4.40
H-BTD	1.63	−6.30	−2.77	3.53	−7.21	−3.56	3.65
H-Ch	1.65	−6.32	−2.72	3.60	−6.24	−2.50	3.74
H-An	1.42	−6.09	−2.94	3.15	−6.0	−2.53	3.47
H-Py	1.44	−6.11	−2.74	3.37	−6.08	−2.66	3.42
H-Per	1.05	−5.72	−3.03	2.69	−5.67	−2.83	2.84

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^aCalculated from oxidation peak potentials of differential pulse voltametric (DPV) traces.

^bComputed DFT values.

Similarly, trends in the E⁰_Oxi also vary across the series. The heterocyclic compounds (H-Pz and H-BTD) show single oxidation peaks at +1.62 V and +1.63 V, respectively. The relatively higher E⁰_Oxi values of these compounds reflect the stabilization of the HOMO by the electron-deficient cores, making oxidation less favourable.⁴⁴ In contrast, among the homocyclic compounds, H-Per shows two distinct oxidation peaks (at +1.05 V and +1.49 V), indicating the two-step oxidation processes. This behavior is attributed to the extended π-conjugation of the perylene core, which enables effective delocalization of positive charge and stabilizes both oxidized states.⁴⁵ This is consistent with the HOMO and HOMO−1 distribution over the central core obtained from DFT calculations. Overall, E⁰_Oxi values follow the order H-Per < H-An < H-Py < H-Ch, indicating that H-Per possesses the highest-lying HOMO, while H-Ch has the deepest HOMO among the homocyclic compounds. The deeper HOMO of H-Ch may be arisen from its specific 6,12-substitution pattern, which limits conjugation and reduces core electron density.

Overall, E_HOMO values of the heterocyclic compounds (H-Pz and H-BTD) are lower than those of the homocyclic compounds, except for H-Ch. This is mainly due to the presence of heteroatoms (N and S) in the heterocyclic cores, which stabilize the molecules through their strong inductive effect.⁴⁶ The experimentally derived and computed HOMO–LUMO energy levels follow the same systematic trend and are in good agreement, confirming the reliability of the electronic structure analysis across the series.

Computational studies

Optimized geometry and molecular electrostatic potential (MEP) analyses

Density functional theory at the B3LYP/6-31G(d,p) level was used to optimize all structures and to evaluate the ground-state geometries (Fig. 4A). In every compound the central aromatic core is essentially planar, whereas the CF₃-pyridyl terminals adopt out-of-plane orientations with distinct dihedral angles relative to the core.

Fig. 4 (A) Optimized geometry with dihedral angles. (B) Molecular electrostatic potential (MEP).

The heterocyclic series displays the smallest dihedral angles, with H-Pz (15.0°) and H-BTD (34.5°), consistent with reduced rotational freedom arising from competing electron-withdrawing effects between the core and the terminals. By contrast, homocyclic cores show substantially larger twists in the order H-An > H-Ch > H-Per > H-Py, reflecting the greater electron density and steric crowding of extended aromatic systems. Importantly, H-An adopts the largest ground-state dihedral (82.5°), which indicates reduced ground-state conjugation with the terminals effectively decoupled.⁴⁷ Geometry relaxation on the S₁ surface drives partial planarization in H-An; the S₁ minimum is closer to planarity (dihedral angle 124.2°), corresponding to a decrease in distance to the nearest planar value by ∼26.9° (Fig. S39). This excited-state planarization increases backbone conjugation, stabilizes S₁ and correlates with the observed long fluorescence lifetime (6.212 ns).⁴⁷ These observations underscore the central role of ground- and excited-state geometry in controlling intramolecular charge redistribution and PL efficiency.

Molecular electrostatic potential maps provide a qualitative view of charge distribution and reactive sites.⁴⁸ In Fig. 4B, the heterocyclic cores (Pz, BTD) exhibit positive potential regions on the ring nitrogens consistent with electron deficiency, whereas the CF₃-pyridyl terminals show negative potential on the pyridyl nitrogens consistent with acceptor character. Homocyclic cores display more uniformly negative potential over the aromatic backbone reflecting extended π electron density. These MEP plots support the interpretation that heterocycles act as strong acceptors while the large homocyclic cores behave as electron-rich backbones in the push–pull systems.

Frontier molecular orbitals (FMOs) and density of states (DOS) analyses

Frontier molecular orbital (FMO) analysis reveals the distinct distribution pattern of frontier orbitals in all molecules because of the electronically diverse central cores and this distribution aligned well with the DOS plots (Fig. 5 and Table 3).

Fig. 5 (A) Frontier molecular orbital (FMOs) at their definite energy levels where E_g is the energy gap between the HOMO and the LUMO. (B) Density of states (DOS) plots for all synthesized compounds at the B3LYP/6-31G(d,p) level of theory.

Table 3 Density of states (DOS) fragment orbital contribution

Compd	HOMO		LUMO
	Core	Terminal	Core	Terminal
H-Pz	51	49	47	53
H-BTD	70	30	81	19
H-Ch	92	8	59	41
H-An	97	3	95	5
H-Py	93	7	70	30
H-Per	94	6	85	15

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For homocyclic A–D–A systems both the HOMO and the LUMO are dominated by core contributions (core contributions ∼ 70–97%) that is the result of the intrinsic π-rich character of extended aromatic cores. Thus, the pronounced core weight of both the HOMO and the LUMO does not contradict a push–pull design but rather implies that charge redistribution upon excitation is delocalized over the conjugated backbone instead of being concentrated at terminal groups.⁴⁹

Moreover, experimental Δµ values (10.30–18.11D) for these systems indicate a substantial excited-state dipole change despite strong LUMO core character. In contrast, H-Pz shows a balanced HOMO/LUMO distribution (HOMO ∼51% core, LUMO ∼53% terminal) consistent with core-to-terminal separation and the heterocyclic acceptor character.

Furthermore, computed HOMO–LUMO gaps (2.84–4.40 eV) reproduce the experimentally calculated energy gaps that validate the accuracy of the chosen B3LYP/6-31G(d,p) level of theory.

Time dependant (TD) DFT studies

Time-dependent TD-DFT calculations were performed at the B3LYP/6-31G(d,p) level in both the gas phase and with chloroform as an implicit solvent to validate the experimentally observed photophysical trends (Fig. 6 and Table 4).

Fig. 6 Computed UV-vis profiles for all compounds. (A) Gaseous phase. (B) Chloroform medium.

Table 4 Computed TD-DFT parameters at B3LYP/6-31G(d,p) for all compounds, where E_x is the excitation energy, f is the oscillator strength, and LHE is the light harvesting efficiency

	Gaseous					Chloroform
Compd	λabs (nm)	Ex (eV)	f (au)	LHE	Major transition (%)	λabs (nm)	Ex (eV)	f (au)	LHE	Major transition (%)
H-Pz	308	4.03	0.94	0.885	H → L (97)	321	3.86	1.11	0.922	H → L (98)
	262	4.73	0.06		H → L+1 (70)	274	4.53	0.05		H−2 → L (51)
H-BTD	378	3.28	0.38	0.580	H → L (98)	387	3.20	0.49	0.678	H → L (99)
	286	4.33	0.35		H → L+1 (70)	303	4.10	0.18		H−1 → L (88)
H-Ch	375	3.30	0.42	0.616	H → L (97)	386	3.21	0.54	0.710	H → L (98)
	255	4.85	0.68		H−1 → L+4 (61)	272	4.56	0.45		H−1 → L+2 (86)
H-An	396	3.13	0.16	0.305	H → L (97)	403	3.08	0.20	0.370	H → L (96)
	241	5.14	0.23		H−5 → L (43)	252	4.92	1.57		H → L+5 (46)
H-Py	390	3.17	0.62	0.762	H → L (94)	407	3.04	0.79	0.837	H → L (96)
	285	4.35	0.22		H → L+5 (44)	291	4.26	0.30		H → L+5 (58)
H-Per	471	2.63	0.73	0.814	H → L (99)	493	2.51	0.89	0.871	H → L (99)
	263	4.70	0.26		H−2 → L+7 (38)	268	4.63	0.34		H → L+7 (36)

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For all compounds, the lowest-energy singlet excitation (S₀ → S₁) is mainly contributed by a HOMO → LUMO transition (Tables S11–S22). The calculated absorption maxima showed close agreement with the experimental trends following the order H-Per > H-An > H-Py > H-BTD > H-Ch > H-Pz. In all cases, implication of chloroform solvent leads to a bathochromic shift relative to the gas phase, reflecting stabilization of the excited states by the polar medium.⁵⁰ Similarly, oscillator strengths (f) and light-harvesting efficiencies (LHE) are systematically enhanced in chloroform compared to the gas phase, indicating more efficient light absorption under solvated conditions.⁵¹

Among the series, H-An exhibits the lowest f, which can be attributed to its relatively orthogonal ground-state geometry that reduces the transition dipole moment and limits effective orbital overlap between the ground and excited states, leading to a more localized excitation on the central anthracene core as evident in the CDD surface contours.^47,52 In contrast, H-Pz shows comparatively large f and LHE despite being non-emissive, suggesting that strong optical absorption doesn’t always result in radiative decay when non-radiative relaxation pathways dominate.⁴⁹ Overall, the TD-DFT results reveal the absorption and electronic trends across the series, while clearly distinguishing excitation probability from emission efficiency.

Intramolecular charge transfer, transition density matrices, exciton binding, and reorganization energy analyses

Charge density difference maps visualize the spatial redistribution of electron density upon photoexcitation from the ground to excited state.⁵³ The CDD maps (Fig. 7A) represent the distinct distribution patterns based on the molecular design. Generally, in the homocyclic A–D–A series the hole distribution is concentrated on the core (∼92–97%) while the electron distribution retains a large core character but with measurable terminal participation (terminal electron contribution ∼5–41%). This pattern indicates backbone-delocalized ICT rather than a strictly localized core → terminal accumulation.

Fig. 7 (A) Charge density difference (CDD) surface contours where the blue colour represents electrons and cyan shows holes, and the corresponding hole/electron heat maps with % delocalization and overlap between two fragments (core and terminal). (B) Transition Density Matrix heat maps at the B3LYP/6-31G(d,p) level of theory.

Transition density matrices provide atom-pair resolution. In all compounds the core–core block dominates the TDM, indicating that the core atoms contribute the largest atom-pair transition density (Fig. 7B). The magnitude of the core-terminal off-diagonal blocks discriminates CT from LE behaviour. H-Pz shows pronounced off-diagonal intensity and an enhanced terminal-terminal signal, consistent with clear core → terminal CT. H-Ch and H-Py show intermediate off-diagonals and thus represent delocalized ICT. H-An and H-Per display dominant diagonal core–core intensity and weak off-diagonals, consistent with localized or backbone-delocalized excitations.

Additionally, total charge transfer and its %age contribution are computed from the excited-state density using fragment population analysis. These values give an idea about how much the electron density is transferred between the two fragments upon excitation.⁵⁴ For the homocyclic derivatives, the computed fragment charge transfer is comparatively lower (7.66–42.77%), while the locally excited (LE) contribution is dominant (57.23–92.34%). This lower q_CT does not imply the absence of charge transfer; rather, it shows the limitation of fragment-based metrics, which quantify population transfer between predefined fragments.⁵⁵ In these systems, excitation is largely delocalized over the extended aromatic backbone, resulting in significant charge redistribution without strong accumulation on the terminal units. This interpretation is consistent with the large experimentally observed Δµ values, which capture global dipole changes over long intramolecular distances rather than localized fragment-to-fragment transfer.³⁶

Overall, H-An exhibits the most pronounced LE character (92.34%), in agreement with its molecular geometry and electronic structure. The nearly linear anthracene core promotes excitation localization on the central backbone, leading to weak core-terminal and strong core-core diagonal coupling as evident in TDM, along with minimal terminal contribution in the CDD maps, and the lowest f computed TD-DFT calculations.⁴⁷ Altogether, these observations confirm that photoexcitation in H-An is predominantly localized on the anthracene core, with limited charge separation, distinguishing it from the more delocalized ICT behaviour observed in H-Ch and H-Py. In contrast, H-Pz is the most canonical fragment CT molecule in the series.

Next, exciton binding energy (E_b) and reorganization energy for holes and electrons (λ_h and λ_e) are computed to determine the propensity for exciton dissociation and the intrinsic carrier mobility (Fig. 8 and Table 5).⁵⁶ Among all, H-Per has the lowest E_b and thus the most favourable tendency for the exciton dissociation, whereas H-Ch and H-BTD have the largest E_b values and are least likely to generate free charges without an appropriate heterojunction.

Fig. 8 Exciton binding and reorganization energies of all compounds.

Table 5 Charge transfer parameters: total transferred charge (q_CT), charge transfer (CT) excitation, localized excitation (LE), exciton binding energy (E_b) and reorganization energy for holes and electrons respectively (λ_h, λ_e) for all compounds

Compd.	qCT (e^−)	CT (%)	LE (%)	Eb	λh	λe
H-Pz	0.442	52.611	47.389	0.306	0.340	0.449
H-BTD	0.112	37.838	62.162	0.372	0.314	0.547
H-Ch	0.338	42.765	57.235	0.432	0.192	0.546
H-An	0.020	7.659	92.341	0.344	0.193	0.688
H-Py	0.305	39.717	60.283	0.246	0.19	0.488
H-Per	0.099	19.324	80.676	0.212	0.167	0.396

---

Generally, hole reorganization energies are generally small for extended cores (H-An, H-Py H-Per) and larger for heterocycles such as H-Pz (λ_h ≈ 0.341 eV). Electron reorganization energies are higher across the series (λ_e ≈ 0.396–0.688 eV) and therefore limit electron mobility relative to holes.

Conclusively, the above results indicate that a high fragment CT contribution alone, as observed for H-Pz, does not guarantee efficient optoelectronic performance; rather, additional parameters such as E_b, λ_h and λ_e must be considered. Overall, homocyclic core containing compounds exhibit backbone-delocalized excitations with balanced charge redistribution and more favourable charge transport characteristics, whereas heterocyclic core-based molecules tend to show localized excitations and therefore require further molecular engineering to achieve comparable performance.

Among the series, H-An displays a long τ, highest Φ_PL, lowest k_r, and dominant core-localized excitation (LE), highlighting its potential as an efficient emitter. In contrast, H-Py shows the largest Δµ upon excitation, while H-Per combines red-shifted absorption, lowest E_b, high LHE, and the lowest λ_h and λ_e, underscoring its suitability for charge transport applications.

Conclusions

The control of photophysical properties such as absorption, emission, fluorescence lifetime, absolute photoluminescence quantum yield, and optimized frontier molecular orbital energies, along with efficient charge transport characteristics, is crucial for the design of promising optoelectronic materials. In this work, we synthesized, characterized, and systemically studied the photophysical, electrochemical and computational properties of six CF₃-pyridyl substituted conjugated materials based on electronically diverse heterocyclic and homocyclic aromatic cores. Interestingly, H-An exhibits a long fluorescence lifetime (τ = 6.212 ns), high Φ_PL (94.6%), and lowest non-radiative decay rate, which is attributed to its linear acene-type structure. H-Py demonstrates the largest dipole-moment change, indicative of a backbone-delocalized intramolecular charge transfer character, while H-Per shows red-shifted absorption, greenish fluorescence, and favourable charge transport properties. In contrast, heterocyclic cores display low Φ_PL and short lifetimes (τ = 0.06–2.38 ns), suggesting that excited-state relaxation is dominated by vibrational non-radiative pathways.

Through molecular design, absorption (309–461 nm), emission (396–544 nm), emission colour (ranging from non-emissive to bluish and greenish), Δµ (10.3–18.11 D), Φ_PL (7.6–94.6%), frontier orbital energy levels (HOMO −5.72 to −6.32 eV; LUMO −2.28 to −3.03 eV), and key computed parameters including dihedral angles (15–82.5°), light-harvesting efficiency (0.37–0.92), exciton binding energy (0.212–0.306 eV), reorganization energies (λ_h = 0.167–0.340 eV; λ_e = 0.396–0.688 eV), and fragment-based charge transfer (0.020–0.442 e⁻) were effectively tuned. Conclusively, these results emphasize that strategic core engineering is an effective tool for modulating the photophysical, electrochemical, and charge transport properties of organic optoelectronic materials.

Experimental section

Materials and methods

All chemicals were purchased from commercial suppliers and used as received without further purification. Solvents employed for column chromatography were obtained commercially and distilled prior to use.

Absorbance and steady-state emission measurements were performed on solutions with concentrations in the range 10⁻⁴–10⁻⁵ M A Shimadzu1800 spectrophotometer was used for UV-Vis measurements over the wavelength range 200–800 nm, while steady-state fluorescence spectra were recorded on an Agilent Cary Eclipse spectrofluorometer. Fluorescence lifetimes were measured on an Edinburgh Instruments FLS1000, and absolute photoluminescence quantum yields (Φ_PL) were determined using the integrating-sphere accessory of the same instrument. For the PLQY (Φ_PL) measurements, the solutions were freshly prepared, and their absorbance was strictly controlled below 0.1 (Fig. S6) to avoid any solute–solvent interactions, formation of aggregates, π–π stacking, and self-reabsorption of the emitted photons. For the H-Pz compound, we couldn’t measure the Φ_PL because of its non-emissive nature as well as unavailability of the filters for the lowest absorbed materials (∼310 nm) at our facility. NMR (¹H, ¹³C and ¹⁹F) spectra were recorded on Bruker spectrometers operating at 600 and 400 MHz. CDCl₃ was used as the primary solvent; for samples with limited solubility, DMSO-d₆ and acetone-d₆ were also used added. Molecular ion peaks were obtained using a GC Trace-1300 coupled with an MS and autosampler AI-1310, Thermo Scientific, while high-resolution mass spectra of H-Py and H-Per were acquired on a Waters Synapt G2-Si High-Definition Mass spectrometer (Fig. S13–S19). IR spectra were recorded on a Bruker ATR-FTIR spectrometer (Fig. S12). Melting points were determined using a standard capillary melting-point apparatus (SMP30).

The experimental dipole moment change was calculated using the Lippert–Mataga relationship as shown in eqn (1)

where Δν represents the Stokes shift (cm⁻¹), µ_g and µ_e are the ground and excited state dipole moments, respectively (D), h is Planck's constant, c is the speed of light, a is the Onsager cavity radius (Å), and Δf is the orientation polarizability parameter defined by eqn (2):

The dielectric constants along with refractive indices for the solvents used in this study are toluene (2.38, 1.496), hexane (1.88, 1.372), petroleum ether (1.84, 1.357), cyclohexane (2.02, 1.426), chlorobenzene (5.62, 1.525), DCM (8.93, 1.424), THF (7.58, 1.407), acetonitrile (35.9, 1.344), MeOH (32.6, 1.328) and DMF (36.7, 1.4305) respectively. The radiative and non-radiative constants were calculated using the following equations eqn (3) and (4)

Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed on a PalmSens 3 e-chem instrument using a three-electrode setup i.e. a glassy carbon working electrode, a platinum wire counter electrode, and an Ag/AgCl reference electrode, while the ferrocene/ferrocenium ion (Fc/Fc⁺) as an internal standard. Measurements were carried out in anhydrous DCM with 0.1 M tetrabutylammonium hexafluorophosphate (Bu₄NPF₆) as the supporting electrolyte and the analyte (3 mg/5 mL). E_HOMO of all compounds was estimated from the oxidation peak potentials of DPV traces using eqn (5) while and E_LUMO by the difference of E_HOMO and the optical band gap using eqn (6). The E⁰_Oxi of ferrocene was calculated to be 0.26 V vs. Ag/AgCl (Fig. S14a). We also tried to acquire CV measurements for H-Pz with ferrocene as an internal standard but in our observation, the H-Pz compound was unstable with ferrocene (Fig. S14b). Thus, we couldn’t test all materials with the inclusion of ferrocene under our testing conditions.

E_LUMO (eV) = E_HOMO (eV) − E_o–o (eV) (6)

Computational studies were performed on the LUMS HPC facility using Gaussian 16; GaussView 6.0 was used to prepare input files and visualize results. Density of states (DOS) plots, DOS fragment contributions, and computed UV-Vis data were processed with GaussSum 2.2. Transition density matrices (TDM), charge density differences (CDD) surface contours, and intramolecular charge-transfer and excitation contribution analyses were carried out using Multiwfn 3.8. Exciton binding energies (E_b) and reorganization energies for holes and electrons (λ_h, λ_e) were calculated using the respective eqn (7)–(10).

LHE = 1 − 10^−f (7)

E_b = ΔE − E_x (8)

λ_h = [E⁰₊ − E₀] + [E₀⁺ − E₊] (9)

λ_e = [E⁰₋ − E₀] + [E₀⁻ − E₋] (10)

Here, E₀ = Ground state energy of the molecule, E₊ and E₋ = Ground state energy of cations and anions, E⁰₊ and E⁰₋ = Neutral energies of cations and anions at the ground state. E₀⁺ and E₀⁻ = Cationic and anionic energies of optimized molecules at the ground state.

Frontier molecular orbital distributions were visualized with Avogadro software. OriginPro 16 (Learning Edition) was used for graphs plotting, linear fitting and visualization.

Chemistry

Synthesis of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,6-bis(trifluoromethyl) pyridine (A). First, a Schlenk flask equipped with an oven dried magnetic stir bar was nitrogen purged followed by evacuation for three cycles. Next, the [Ir(OMe)(COD)]₂ precatalyst (9.9 mg, 0.015 mmol, 1.5 mol%), 2,2′-bipyridine ligand (4 mg, 0.025 mmol, 2.5 mol%), pinacolborane (HBPin) (192 mg, 218 µL, 1.5 mmol, 1.5 equiv.), and 2,6-bis(trifluoromethyl)pyridine substrate (215 mg, 1 mmol, 1 equiv.) were added in the Schlenk flask respectively. Then, the Schlenk flask was closed, and the reaction mixture (RM) was heated at 80 °C using an oil bath for 3 h. The reaction progress was monitored by TLC and GC-MS analyses. Upon completion of reaction, the flask was taken out from the oil bath, cooled at room temp., and the RM was exposed to air. The RM was concentrated under vacuum using a rotary evaporator to remove volatiles. The crude RM was then purified by column chromatography using silica gel as a stationary phase and hexane and DCM as eluents.

Compound A was isolated as a white solid (465 mg, 89%); (hexanes/DCM 1 : 3, R_f 0.41), mp 86–88 °C, GC-MS (EI), RT: 7.28, m/z (% relative intensity) 341.13 (M⁺, 5), 326 (100), 322 (15), 299 (14), 281 (9), 255 (11).

Melting point, NMR and GC-MS data were in agreement with previously reported data in the literature.²⁵

General procedure for Suzuki coupling reactions (H-Y)

All reactions of this study were carried out in an oven dried Schlenk flask having a magnetic stir bar. First, the Schlenk flask was nitrogen purged followed by evacuation for three cycles. Under positive supply of N₂, pre-catalyst Pd(OAc)₂ (9 mg, 0.04 mmol, 4 mol %), ligand SPhos (32.8 mg, 0.08 mmol, 8 mol %), 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,6-bis(trifluoromethyl)pyridine (853 mg, 2.5 mmol, 2.5 equiv.) for entries (H-Pz to H-Per), limiting substrates [(1 mmol each, 1 equiv.), base K₂CO₃ (414.6 mg, 0.03 mmol, 3 equiv.) and 4 mL of toluene solvent were added in aforesaid order. After this, the Schlenk flask was closed tightly and placed in an oil bath maintained at 80 °C for 8–24 h. The reaction progress was monitored by TLC and GC-MS analyses by taking a crude mixture under a N₂ atmosphere. Upon completion of reaction, the flask was taken out from the oil bath, cooled to room temp., and exposed to air. Next, the mixture inside the flask was extracted with DCM and EtOAc (20–30 mL × 3) and concentrated under vacuum using a rotary evaporator to remove volatiles. The obtained crude mixture was then purified by column chromatography using silica gel as the stationary phase, hexanes and DCM as eluents.

Synthesis of 2,5-bis(2,6-bis(trifluoromethyl)pyridin-4-yl)pyrazine (H-Pz). The general procedure was applied to 2,5-dibromopyrazine (238 mg, 1 mmol, 1 equiv.) for 8 h, the H-Pz compound was isolated as a light-yellow solid (465 mg, 92%); (hexanes, R_f 0.74), mp 214–216 °C, ¹H NMR (400 MHz, CDCl₃) δ 9.39 (s, 2H), 8.61 (s, 4H);¹³C NMR (151 MHz, CDCl₃) δ 150.4 (q, ²J_C–F = 37.7 Hz, C), 148.6, 146.6, 142.3, 120.9 (q, ¹J_C–F = 276.3 Hz, CF₃),120.6; ¹⁹F NMR (565 MHz, CDCl₃) δ −68.02 (s, CF₃); GC-MS (EI), RT: 11.77, m/z (% relative intensity) 506 (M⁺, 51), 486 (26), 437 (5), 253 (9), 239 (90) 170 (100), 150 (18) 143 (12); FT-IR (neat) [small upsilon, Greek, macron] (cm⁻¹) = 1613, 1389, 1326, 1286, 1264, 1190, 1129, 1101, 1019, 940, 919, 899, 856, 818, 719, 694, 658.

Synthesis of 4,7-bis(2,6-bis(trifluoromethyl)pyridin-4-yl)benzo[c][1,2,5]thiadiazole (H-BTD). The general procedure was applied to 4,7-dibromobenzo[c][1,2,5]thiadiazole (294 mg, 1 mmol, 1 equiv.) for 19 h; the H-BTD compound was isolated as a red solid (400 mg, 71%); (hexanes/DCM 3 : 1, R_f 0.82), mp 202–204 °C, ¹H NMR (400 MHz, CDCl₃) δ 8.58 (s, 4H), 8.12 (s, 2H); ¹³C NMR (151 MHz, CDCl₃) δ 153.3, 149.9, (q, ²J_C–F = 36.2 Hz, C) 147.9, 131.1, 129.4, 123.3, 121.2 (q, ¹J_C–F = 274.8 Hz, CF₃); ¹⁹F NMR (565 MHz, CDCl₃) δ −67.90 (s, CF₃); GC-MS (EI), RT: 13.89, m/z (% relative intensity) 562 (M⁺, 100), 493 (36), 473 (26), 403 (7), 202 (9); FT-IR (neat) [small upsilon, Greek, macron] (cm⁻¹) = 3095, 2922, 2850, 2015, 1608, 1394, 1333, 1281, 1200, 1129, 976, 905, 854, 803, 721, 701.

Synthesis of 6,12-bis(2,6-bis(trifluoromethyl)pyridin-4-yl)chrysene (H-Ch). The general procedure was applied to 6,12-dibromochrysene (386.1 mg, 1 mmol, 1 equiv.) for 24 h; the H-Ch compound was isolated as a yellow solid (402 mg, 61%); (hexanes/DCM 3 : 1, R_f 0.7), mp 304–306 °C, ¹H NMR (400 MHz, CDCl₃) δ 8.90 (d, J = 8.5 Hz, 2H), 8.70 (s, 2H), 8.19 (s, 4H), 7.85 (dd, J = 15.4, 7.8 Hz, 4H), 7.74 (t, J = 7.6 Hz, 2H); ¹³C NMR (151 MHz, CDCl₃) δ 153.4, 149.7 (q, ²J_C–F = 36.2 Hz, C), 135.8, 131.2, 129.8, 128.5, 128.5, 128.4, 125.9, 124.8, 123.4 (q, ¹J_C–F = 274.8 Hz, CF₃), 120.4, 118.6; ¹⁹F NMR (565 MHz, CDCl₃) δ −67.70 (s, CF₃); GC-MS (EI), RT: 20.45, m/z (% relative intensity) 654 (M⁺, 100), 564 (8), 371 (15), 297 (17), 238 (19), 174 (10); FT-IR (neat) [small upsilon, Greek, macron] (cm⁻¹) = 3080, 2931, 1603, 1520, 1440,1382, 1280, 1179, 1131, 1094, 987, 916, 884, 854, 763, 695.

Synthesis of 9,10-bis(2,6-bis(trifluoromethyl)pyridin-4-yl)anthracene (H-An). The general procedure was applied to 9,10-dibromoanthracene (336 mg, 1 mmol, 1 equiv) for 20 h; the H-An compound was isolated as a colourless solid (506 mg, 84%); (hexanes/DCM 3 : 1, R_f 0.72), mp 312–314 °C, GC-MS (EI), RT: 13.57, m/z (% relative intensity) 604 (M⁺, 100), 535 (11), 465 (15), 370 (44), 300 (29), 251(33) 223 (11); FT-IR (neat) [small upsilon, Greek, macron] (cm⁻¹) = 3045, 2921, 1607, 1426, 1339, 1279, 1188, 1133, 1029, 984, 916, 856, 806, 762,726, 698, 665, 647.

The mp, NMR and GC-MS data of this compound are in agreement with the literature.²⁵

Synthesis of 1,6-bis(2,6-bis(trifluoromethyl)pyridin-4-yl)pyrene (H-Py). The general procedure was applied to 1,6-dibromopyrene (360.1 mg, 1 mmol, 1 equiv) for 24 h; the H-Py compound was isolated as a light green solid (481 mg, 76%); (hexanes, R_f 0.37), mp 324–326 °C, ¹H NMR (400 MHz, CDCl₃) δ 8.38 (d, J = 7.9 Hz, 2H), 8.24 (d, J = 9.2 Hz, 2H), 8.18 (s, 4H), 8.07 (dd, J = 12.8, 8.6 Hz, 4H); ¹³C NMR (101 MHz, acetone-d₆) δ 154.6, 149.3 (q, ²J_C–F = 36 Hz, C), 134.0, 132.9, 130.0, 129.4, 129.2, 126.8, 125.9, 125.5, 122.3 (q, ¹J_C–F = 274 Hz, CF₃); ¹⁹F NMR (377 MHz, CDCl₃) δ −67.70 (s, CF₃); HRMS (ESI+): m/z [M + H]⁺ calcd for C₃₀H₁₂F₁₃N₂ [M + H]⁺: 629.0887; found: 629.0878; FT-IR (neat) [small upsilon, Greek, macron] (cm⁻¹) = 3092, 2926, 2322, 2162, 1608, 1440, 1390, 1274, 1195, 1126, 1053, 994, 908, 844, 803, 723, 691.

Synthesis of 3,9-bis(2,6-bis(trifluoromethyl)pyridin-4-yl)perylene (H-Per). The general procedure was applied to 3,9-dibromoperylene (410.1 mg, 1 mmol, 1 equiv.) for 24 h. Following the general procedure, the H-Per compound was isolated as a red solid (533 mg, 79%); (hexanes/DCM 5 : 1, R_f 0.52), mp 323–326 °C, ¹H NMR (400 MHz, CDCl₃) δ 8.38 (ddd, J = 7.8, 6.4, 3.9 Hz, 4H), 8.07 (s, 4H), 7.66–7.60 (m, 4H), 7.52 (d, J = 7.8 Hz, 2H), ¹³C NMR (151 MHz, CDCl₃) δ 153.0, 149.6 (q, ²J_C–F = 36.2 Hz, C), 135.4, 132.8, 132.1, 131.9, 129.3, 128.7 ((q, ³J_C–F = 10.6 Hz, C), 125.3, 124.9, 124.5,122.2, 121.3(q, ¹J_C–F = 274.8 Hz, CF₃), 120.9; HRMS (ESI+): m/z [M + H]⁺ calcd for C₃₄H₁₅F₁₂N₂: 679.1044; found: 679.1021; FT-IR (neat) [small upsilon, Greek, macron] (cm⁻¹) = 3088, 2929, 2854, 2162, 1608, 1412, 1375, 1273, 1190, 1131, 933, 906, 882, 857, 830, 808, 724, 629.

Author contributions

Hasan Yaqoob: investigation, methodology, data curation, visualization, formal analysis, writing – original draft, conceptualization; Nimra Arif: methodology, formal analysis; Rahman Shah Zaib Saleem: software, formal analysis, validation; Jafar Iqbal Khan: formal analysis, validation, investigation; Raja Shahid Ashraf: resources, validation, writing – review and editing; Christian B. Nielsen: conceptualization, resources, validation, supervision, writing – review and editing; Ghayoor Abbas Chotana: writing – review and editing, supervision, resources, funding accusation, project administration.

Conflicts of interest

The authors declare no competing financial or non-financial interests.

Data availability

The spectroscopic data (¹H and ¹³C NMR, and mass spectra) supporting this article have been uploaded as part of the supplementary information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d6ma00215c.

Acknowledgements

We are thankful to the Lahore University of Management Sciences (LUMS) for providing Lab infrastructure and Syed Babar Ali Foundation and LUMS Central Labs for analytical facilities. This research was funded by the Higher Education Commission of Pakistan (HEC) grant number NRPU-5903 (to GAC), and by the Lahore University of Management Sciences through the Faculty initiative fund (FIF) grant number FIF-327 (to GAC). HY is thankful to HEC Pakistan for providing an IRSIP fellowship (57th batch – 72611) to join “The Nielsen Lab” as a visiting PhD student at the Queen Mary University of London (QMUL), UK. We thank Dr Stoichko Dimitrov (SPCS) and Dr Flurin Eisner (SEMS), along with their PhD students Chun Hei Lau and Stanley Cazaly (QMUL), for providing access to the PL instrument facility and for their valuable assistance in acquiring the PL data. HY offers sincere gratitude to Dilara Gunturkun and Dr Kalidass Kollimalaian for their assistance in electrochemical measurements. This paper is dedicated to Syed Babar Ali on his 100th birthday.

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