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DOI: 10.1039/D5DT00618J (Paper) Dalton Trans., 2025, 54, 10234-10245

Electron deficient β-trisubstituted porphyrins: synthesis, structural, spectral, and electrochemical studies and their intensity-dependent third-order nonlinear optical properties†

Reena Jangra‡ a, Amritha J. Nair‡ a, Albin Kuriakose b, Jitendra Nath Acharyya b, G. Vijaya Prakash *b and Muniappan Sankar *a
aDepartment of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247667, India. E-mail: m.sankar@cy.iitr.ac.in
bNanophotonics Lab, Department of Physics, Indian Institute of Technology Delhi, New Delhi-110016, India. E-mail: prakash@physics.iitd.ac.in

Received 14th March 2025 , Accepted 21st May 2025

First published on 21st May 2025

Abstract

A series of electron-deficient β-trisubstituted 12-nitro-5,10,15,20-tetraphenyl-2,3-bis(trifluoromethyl)porphyrins, abbreviated as H2TPP(NO2)(CF3)2, and their metal complexes MTPP(NO2)(CF3)2 (where M = CoII, NiII, CuII, and ZnII) have been prepared and characterised by various spectroscopic techniques. Single crystal X-ray analysis revealed the saddle-shaped configuration of CoTPP(NO2)(CF3)2, NiTPP(NO2)(CF3)2 and CuTPP(NO2)(CF3)2 with the average deviation of the 24 core atoms from the mean porphyrin plane (Δ24) ranging from ±0.492 to ±0.499 Å and the average displacement of β-pyrrole carbons from the porphyrin mean plane (ΔCβ) ranging from ±0.926 to ±1.005 Å. H2TPP(NO2)(CF3)2 exhibited a 28 nm red shift in the B-band and a 102 nm red shift in the longest Q-band (Qx(0,0)) as compared to H2TPP. In 1H NMR, the inner imino protons of H2TPP(NO2)(CF3)2 were observed at −1.72 ppm, which is significantly downfield shifted compared to H2TPP. The first ring reduction potential of MTPP(NO2)(CF3)2 (M = 2H, CoII, NiII, CuII, and ZnII) is positively shifted by 280–620 mV compared to their corresponding MTPPs. Notably, it is observed that the synthesized MTPP(NO2)(CF3)2 porphyrins are readily reduced compared to their MTPPs. Intensity-dependent third-order nonlinear optical property studies demonstrated that the synthesized asymmetric β-substituted electron-deficient porphyrins exhibit significant two-photon absorption coefficients (β = 0.04–8.10 × 10−10 m W−1) and two-photon absorption cross-section values (σ2PA = 0.02–1.67 × 106 GM). Additionally, the materials exhibit self-defocusing negative nonlinear refraction (n2 = (−) 1.08–40.27 × 10−17 m2 W−1). The extracted NLO data suggest the potential of the investigated porphyrins for future optoelectronic and advanced material applications.

Introduction

The potential application of nonlinear optical (NLO) materials in optical computing, image processing, optical fibers, optical switching, optical limiting, optical communication, and optical data storage has garnered significant research attention in this field.1–11 The development of novel NLO materials exhibiting strong NLO responses and high stability is urgently required to meet the demands of various applications across different fields. In this regard, porphyrins emerge as particularly promising candidates for nonlinear optical properties.12,13 This is attributed to their highly delocalized aromatic π-electron systems, substantial stability, conformational flexibility, and potential for versatile structural modifications.14–34 However, additional factors such as the position, nature, and polarizability of the rings or nature of the substituents, intramolecular and transition dipole moments, and the orthogonality of the substituents, molecular dihedral angle, and oxidation state of the metal ions can also significantly enhance the NLO response.35 These features collectively improve their suitability for tuning NLO responses. Ongoing research in developing NLO materials has yielded diverse porphyrin structures. These structures include push–pull porphyrins,36 symmetric15,17,18 and asymmetric porphyrins,19–21,37 porphyrin oligomers,22–24 expanded porphyrins28 and porphyrin arrays.29–32 The third-order NLO properties of porphyrin derivatives can be modulated through metal complexation,38,39π-conjugation, and functionalization.40,41 In contrast, the second-order NLO properties of porphyrin and its derivatives have been infrequently studied, primarily due to the centrosymmetric nature of pristine porphyrins.42,43 However, by disturbing the centrosymmetry, porphyrin derivatives could exhibit significant NLO responses; keeping this in mind, our research group is currently focused on synthesizing unsymmetrical porphyrins and corroles for NLO applications. In 2017, Yadav and co-workers synthesized push–pull trans-A2B-corroles and studied their femtosecond third-order NLO properties.44 In 2020, Rathi and co-workers prepared unsymmetrical push–pull porphyrins and characterized their effect on metal insertion in ultrafast NLO materials.45 In 2021, Kumar and coworkers studied the strong two-photon absorption of meso-functionalized trans-A2BC porphyrins.46 In 2022, Rohal and co-workers synthesized unsymmetrical β-dicyanovinyl appended push–pull porphyrins as promising two-photon absorbers, and β-tetracyanobutadiene appended porphyrins as cost-effective optical limiters.47,48 Bulbul and co-workers synthesized unsymmetrically β-functionalized π-extended porphyrins as efficient two-photon absorbers.49 Yadav and co-workers studied ultrafast dynamics and strong two-photon absorbers of nonplanar β-functionalized push–pull copper corroles with mixed substituted patterns.50 In 2023, Kumari and co-workers prepared a push–pull octaphenylporphyrin with different substituted patterns and characterized its ultrafast dynamics and NLO studies.51 In 2024, Rohal and co-workers synthesized electron-deficient, nonplanar β-heptasubstituted porphyrin derivatives that exhibit an interesting three-photon absorption phenomenon.52 In 2024, Bulbul and coworkers synthesized highly substituted Ni(II) porphyrins and meso-β monofused porphyrins and explored their third-order nonlinear optical properties.53,54 Recently, Bulbul and coworkers synthesized meso-β, β–β′-trifused porphyrins and studied their femtosecond third-order nonlinear optical properties.55

Research on unsymmetrical porphyrins has predominantly focused on push–pull porphyrins, with limited studies on electron-deficient unsymmetrical porphyrins due to the challenges in their synthesis. However, unsymmetrically electron-deficient antipodal β-trisubstituted porphyrins have shown distinct electronic and photophysical properties, suggesting significant potential for broader future applications. Herein, the present work illustrates the synthesis of unsymmetrically electron-deficient β-trisubstituted porphyrins in good yields, characterized by different spectroscopic techniques and single crystal XRD, and explores their intensity-dependent third-order NLO properties.

Results and discussion

Synthesis and characterization

A series of electron-deficient β-trisubstituted 12-nitro-5,10,15,20-tetraphenyl-2,3-bis(trifluoromethyl)porphyrins (H2TPP(NO2)(CF3)2) and their metal complexes MTPP(NO2)(CF3)2 (M = CoII, NiII, CuII and ZnII) were synthesized (see Chart 1) and thoroughly characterized using various spectroscopic techniques including UV-vis, fluorescence, and NMR spectroscopy, elemental analysis, single crystal X-ray analysis, and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Following established literature procedures, H2TPP(NO2)Br2 and its copper complex were prepared.56 The copper complex CuTPP(NO2)Br2 was charged with Chen's reagent (FSO2CF2CO2CH3) in the presence of a palladium catalyst (Pd(0)) and CuI as a co-catalyst, resulting in the formation of CuTPP(NO2)(CF3)2 with a 65% conversion. The CuTPP(NO2)(CF3)2 complex was demetallated using H2SO4, followed by remetallation with various metal salts, including CoII, NiII, and ZnII (see Scheme 1).
image file: d5dt00618j-c1.tif
Chart 1 Molecular structure of electron-deficient β-trisubstituted porphyrins.

image file: d5dt00618j-s1.tif
Scheme 1 Synthetic scheme for MTPP(NO2)(CF3)2.

Single crystal X-ray diffraction analysis

Single crystal X-ray diffraction interpretation determined the exact spatial configuration and connectivity of trifluoromethyl (CF3) substituents at the pyrrolic carbons of porphyrins. The crystallization process of CoTPP(NO2)(CF3)2, NiTPP(NO2)(CF3)2, and CuTPP(NO2)(CF3)2 described in this study involved the slow diffusion of hexane into a saturated solution of porphyrins in CHCl3 at ambient temperature. The displacement of porphyrin 24 core atoms from the mean plane is shown in Fig. S1 in the ESI.† The crystallographic data, average bond lengths and angles of CoTPP(NO2)(CF3)2, NiTPP(NO2)(CF3)2, and CuTPP(NO2)(CF3)2 are presented in Tables S1 and S2, respectively, in the ESI.† The ORTEP structures (top and side views) of CoTPP(NO2)(CF3)2, NiTPP(NO2)(CF3)2, and CuTPP(NO2)(CF3)2 are shown in Fig. 1. CoTPP(NO2)(CF3)2 and CuTPP(NO2)(CF3)2 are crystallized in a monoclinic crystal system with a P21/c space group, whereas NiTPP(NO2)(CF3)2 is crystallized in the triclinic system with a P[1 with combining macron] space group. The single crystal X-ray analysis revealed the saddle-shaped configuration of all three porphyrins, with a mean plane deviation of 24 atoms (Δ24) ranging from ±0.492 to ±0.499 Å from the reference plane, although the deviation of β-carbon atoms (ΔCβ) was found to be in the range of ±0.926–±1.005 Å (see Fig. S1 in the ESI†), which is considerably higher than those reported for the published structures, H2TPP(CF3)2, NiTPP(NO2)(Ph)2(pyridine), ZnTPP(NO2)(PE)2(CH3OH), ZnTPP(NO2)Br2(CH3OH) and H2TPP(NO2)(Th)2 (Δ24 = ±0.061–±0.377 Å and ΔCβ = ±0.072–±0.750 Å).56,57
image file: d5dt00618j-f1.tif
Fig. 1 ORTEP diagrams showing top (upper) and side views (lower) of CoTPP(NO2)(CF3)2 (a and d), NiTPP(NO2)(CF3)2 (b and e) and CuTPP(NO2)(CF3)2 (c and f). Solvates are omitted for clarity, and the meso-phenyls are removed for clarity in the side views (d–f). Color codes: C (slate blue), N (orchid), O (red), H (violet-red), F (lime green), Co (brown), Ni (orange), and Cu (cool copper).

The nonplanarity of the porphyrin macrocycle is attributed to steric repulsion among the peripheral substituents, which necessitates strain release through adjustments in bond lengths and angles. Specifically, the C–C bond distance between the β-pyrrole carbon atoms (Cβ–Cβ bond lengths) bearing three β-substituents is longer than the Cβ′–Cβ′ distances, where the antipodal pyrroles are unsubstituted (see Table S2 in the ESI†). Notably, the N–M–N and N′–M′–N′ angles, ranging from 169.37° to 174.41°, deviate from 180°, signifying the nonplanar conformation of the M–(N)4 core. Density functional theory (DFT) was employed for the free base and other metal complexes to carry out the complete geometry optimization.

Electronic spectral studies

The optical absorption properties of electron-deficient β-functionalized MTPP(NO2)(CF3)2 (M = 2H, CoII, NiII, CuII, and ZnII) porphyrins were investigated in CH2Cl2 at 298 K. The electronic absorption spectra of porphyrin macrocycles are significantly influenced by the nature of the core metal ions, the presence of peripheral substituents, the shape of the molecule, and the extent of π-conjugation. The UV-visible absorption spectra of the presented porphyrins are shown in Fig. 2(a). The nonplanar conformation of the macrocycle is known to induce a distinctive red shift in their optical absorption properties.58–60Table 1 lists the optical absorption spectral data of all the presented porphyrins. H2TPP(NO2)(CF3)2 exhibited a 9 nm red shift in the B-band and a 67 nm red shift in the longest Q-band (Qx(0,0)) as compared to H2TPP(NO2)Br2, which can be attributed to the more electron-accepting effect of trifluoromethyl groups functionalized at the β-position of the pyrrole unit and the nonplanar conformation of the synthesized porphyrins, as demonstrated by the DFT calculations. MTPP(NO2)(CF3)2, M = CoII, NiII, CuII, and ZnII, exhibited a 6–9 nm hypsochromic shift in the B-band as compared to H2TPP(NO2)(CF3)2, because of the stabilization of the highest occupied molecular orbital (HOMO) after insertion of metal. H2TPP(NO2)(CF3)2 exhibited a 28 nm bathochromic shift in the Soret band and a 105 nm red shift in the longest Q-band (Qx(0,0)) as compared to H2TPP.61 This phenomenon is likely attributable to the conjugative or inductive interactions of the substituents with the π-system, as well as the nonplanarity of the porphyrin macrocycle, as demonstrated by the DFT calculations. H2TPP(NO2)(CF3)2 showed a 19 nm red shift in the B-band and an 86 nm red shift in the longest Q-band (Qx(0,0)) as compared to H2TPP(NO2).56 H2TPP(NO2)(CF3)2 exhibited a 1–6 nm bathochromic shift in the Soret band and 48–64 nm in the longest Q-band that resembled the mixed trisubstituted porphyrins as reported in the literature, which suggests the strongest electron-accepting effect of the trifluoromethyl group as compared to cyano, bromo, phenyl, 2-thienyl (Th) and phenylethynyl groups.56 A similar type of disubstituted porphyrin (H2TPP(CF3)2) reported in the literature showed a 6 nm blue shift in the B-band and a 42 nm blue shift in the longest Q-band compared to the synthesized H2TPP(NO2)(CF3)2, due to the presence of an electron-withdrawing nitro group.57
image file: d5dt00618j-f2.tif
Fig. 2 (a) Electronic absorption spectra of MTPP(NO2)(CF3)2 in CH2Cl2 at 298 K. Fluorescence spectra of (b) H2TPP(NO2)(CF3)2 and (c) ZnTPP(NO2)(CF3)2 in CH2Cl2 at 298 K.
Table 1 Electronic spectral data of the synthesized porphyrins in CH2Cl2 at 298 Ka
Porphyrins λ abs, nm λ em, nm ϕ f
a Values in parentheses refer to ε × 10−3 (M−1 cm−1).
H2TPP(NO2)(CF3)2 445 (204), 557 (10), 750 (18) 766 0.11
CoTPP(NO2)(CF3)2 437 (132), 617 (20)
NiTPP(NO2)(CF3)2 439 (121), 614 (18)
CuTPP(NO2)(CF3)2 436 (166), 628 (18)
ZnTPP(NO2)(CF3)2 439 (145), 633 (13) 752 0.034

The synthesized free base and ZnIIβ-functionalized porphyrins were characterized using fluorescence spectroscopy to investigate the influence of nonplanarity and substitutions. Fig. 2b and c show the steady-state emission spectra of the free base and ZnII complex taken in CH2Cl2 at 298 K, and the emission data are tabulated in Table 1. H2TPP(NO2)(CF3)2 showed a 48 nm red-shifted emission compared to H2TPP in CH2Cl2. ZnTPP(NO2)(CF3)2 revealed a notable 103 nm red-shifted emission compared to ZnTPP. A significant red shift is observed due to the presence of electron-accepting nitro and trifluoromethyl groups. H2TPP(NO2)(CF3)2 and ZnTPP(NO2)(CF3)2 showed qualitative quantum yields comparable to those of H2TPP and ZnTPP.

NMR spectral studies and mass spectrometry

The 1H NMR spectra of the synthesized porphyrins, MTPP(NO2)(CF3)2 (where M = 2H, NiII and ZnII), were obtained in CDCl3 at 298 K. The 1H NMR signals for all the synthesized porphyrins were attributed to meso-phenyl protons, β-pyrrole protons, and inner imino protons in the case of the free base. The integration of the proton signals is consistent with the synthesized porphyrin structures. Fig. S2–S4 in the ESI† show the 1H NMR spectra of H2TPP(NO2)(CF3)2, NiTPP(NO2)(CF3)2 and ZnTPP(NO2)(CF3)2. A singlet peak at 8.85 ppm is observed for the synthesized free base porphyrin corresponding to the β-proton adjacent to the β-nitro group. The remaining four β-protons exhibited one doublet of triplet and one multiplet at 8.70 ppm and 8.60 ppm, respectively (see Fig. S2 in the ESI†). The meso-phenyl protons exhibit a multiplet between 7.76 and 8.28 ppm. The inner imino protons were observed at −1.72 ppm. Notably, it is observed that the resonance of inner imino protons is highly downfield shifted (0.81–0.93 ppm) as compared to the mixed trisubstituted porphyrins reported in the literature, due to the more electron-accepting effect of the trifluoromethyl group and non-planar conformation.56 The nonplanarity of the macrocycle induces broad features in the resonance of the imino protons, shifting them to the downfield region compared to those in planar porphyrins.62,63 Similarly, NiII and ZnII complexes showed analogous spectra to H2TPP(NO2)(CF3)2. The integration of all the proton signals corresponded well with the proposed structures.

19F and 13C NMR spectra of ZnTPP(NO2)(CF3)2 are recorded in CDCl3 and shown in Fig. S5 and S6, respectively, in the ESI.† In the 19F NMR spectrum, ZnTPP(NO2)(CF3)2 shows two peaks at −46.54 ppm (3F) and −46.70 ppm (3F). 13C NMR spectra showed macrocycle signals ranging from 119.73 to 152.79 ppm.

All the synthesized porphyrins were characterized by MALDI-TOF mass spectrometry. All the mass spectra were recorded in positive ion mode using CH2Cl2 as a solvent at 298 K and are shown in Fig. S7–S11 in the ESI.†

DFT studies

To investigate the influence of substituents at the β-pyrrolic position of the porphyrin macrocycle and to validate the experimental results, we performed the optimization of the ground state geometries for the electron-deficient β-trisubstituted porphyrins MTPP(NO2)(CF3)2, M = 2H, CoII, NiII, CuII, and ZnII in the gas phase using Gaussian 16 software. The calculations were performed with the B3LYP functional set and 6-31G basis set for the free base, while the LANL2DZ basis set was used for the metal complexes. The synthesized porphyrins’ optimized geometry (top and side views) is shown in Fig. S12 in the ESI† and frontier molecular orbitals (FMOs) are shown in Fig. S13 in the ESI.† According to Gouterman's four orbital models, the highest occupied molecular orbitals (HOMOs) exhibit electron density contribution from meso-carbon and pyrrolic nitrogen, which corresponds to the a2u type, whereas HOMO−1 exhibits electron density at pyrrolic carbons, which is classified as the a1u type. The lowest occupied molecular orbitals (LUMOs) exhibited electron density at opposite substituted pyrrolic moieties, meso-carbons, and the nitro group, whereas LUMO−1 showed electron density at the opposite unsubstituted pyrrolic moieties, meso-carbons, and the nitro group. The calculated average bond lengths and angles are tabulated in Table S3 in the ESI.† The peripheral substituents may induce steric hindrance in the porphyrins, which can be alleviated by modifying the bond angles and lengths in the nonplanarity of the ring. Electron-accepting moieties increase the Cβ–Cβ and M–N bond lengths as compared to the Cβ′–Cβ′ and M–N′ bond lengths of the synthesized porphyrins MTPP(NO2)(CF3)2, M = 2H, CoII, NiII, CuII, and ZnII (see Table S3 in the ESI†). The synthesized porphyrins exhibited a mean plane deviation of Δ24 atoms ranging from ±0.318 to ±0.768 Å, whereas the deviation of ΔCβ ranges from ±0.389 to ±0.875 Å. The theoretically calculated ground state dipole moment in the gas phase of the synthesized porphyrins ranges from 6.42 to 7.75 Debye (D) and is listed in Table S4 in the ESI.†

Electrochemical studies

The electrochemical redox potentials of the macrocyclic π-system are affected by the nature of the β-substituents, nonplanar conformation, and the core metal ions. To elucidate the combined effect of macrocyclic nonplanarity and the electron-accepting nature of the β-functionalized trifluoromethyl substituent, we investigated the electrochemical redox characteristics of the presented porphyrins in CH2Cl2 with 0.1 M TBAPF6 as the supporting electrolyte at 298 K using cyclic voltammetry. Fig. 3 shows the cyclic voltammogram, and Table 2 lists the redox potential (vs. Ag/AgCl) data of all the synthesized porphyrins. The synthesized free base porphyrin, H2TPP(NO2)(CF3)2, exhibits three successive one-electron reversible oxidations and one two-electron reversible reduction, whereas CoTPP(NO2)(CF3)2 undergoes three successive one-electron reversible oxidations and two one-electron reversible reductions. The first oxidation and reduction of CoII correspond to the metal-centered redox activity, well-documented in the literature,64,65 whereas the second and third oxidations correspond to the ring-centered redox activity. NiTPP(NO2)(CF3)2 demonstrates one successive two-electron oxidation and two one-electron reductions. CuTPP(NO2)(CF3)2 reveals two successive one-electron reversible oxidation and reduction peaks. In comparison, ZnTPP(NO2)(CF3)2 exhibited two successive one-electron reversible oxidations and two close reduction processes merged to produce an average potential at −0.85 V (see Fig. 3).
image file: d5dt00618j-f3.tif
Fig. 3 Cyclic voltammograms (CVs) of all the synthesized porphyrins in CH2Cl2 at 298 K. Scan rate - 0.1 V sec−1.
Table 2 Comparative electrochemical redox data (vs. Ag/AgCl) of the synthesized porphyrins (MTPP(NO2)(CF3)2), with their parent porphyrinsa MTPP and MTPP(NO2) in CH2Cl2 containing 0.1 M TBAPF6 at 298 K
Porphyrins Oxidation (V) Reduction (V) ΔE (V)
I II III I II III
a Electrochemical data of MTPP and MTPP(NO2) are taken from ref. 56.
H2TPP 1.00 1.34 −1.23 −1.54 2.23
H2TPP(NO)2 1.10 1.28 −0.87 −1.08 1.97
H 2 TPP(NO) 2 (CF 3 ) 2 0.99 1.21 1.53 −0.52 1.51
CoTPP 0.85 1.06 1.32 −0.86 −1.38 2.44
CoTPP(NO)2 0.91 1.17 1.42 −0.66 −1.29 −1.89 2.46
CoTPP(NO) 2 (CF 3 ) 2 0.88 1.21 1.47 −0.43 −1.10 2.31
NiTPP 1.02 1.32 −1.28 −1.72 2.30
NiTPP(NO)2 1.18 1.31 −0.94 −1.21 2.12
NiTPP(NO) 2 (CF 3 ) 2 1.32 −0.60 −0.84 1.92
CuTPP 0.97 1.35 −1.32 −1.71 2.29
CuTPP(NO)2 1.07 1.44 −0.98 −1.23 2.05
CuTPP(NO) 2 (CF 3 ) 2 1.02 1.52 −0.70 −0.91 1.72
ZnTPP 0.83 1.14 −1.36 −1.76 2.19
ZnTPP(NO)2 0.91 1.21 −1.04 −1.19 1.95
ZnTPP(NO) 2 (CF 3 ) 2 0.89 1.18 −0.85 1.74

The impact of the β-substituted trifluoromethyl group (MTPP(NO2)(CF3)2) on the porphyrin macrocycle is characterized by comparing the first reduction potential peak with those of the corresponding MTPP(NO2) and MTPPs (see Table 2). It is observed that the first ring reduction potential of MTPP(NO2)(CF3)2 is positively shifted by 190–350 mV and 280–680 mV compared to their corresponding MTPP(NO2) and MTPPs, respectively.56β-Substituents also influence the metal-centered redox potential properties; for instance, the first metal-centered reduction potential of CoTPP(NO2)(CF3)2 is 230 mV and 430 mV anodically shifted compared to CoTPP(NO2) and CoTPP, respectively (see Table 2).56

Notably, it is observed that the first ring reduction potential of MTPP(NO2)(CF3)2 is 89–342 mV anodically shifted compared to the reported trisubstituted porphyrins MTPP(NO2)X2 (X = Br, Ph, PE and Th) in the literature.56 However, among the MTPP(NO2)(CF3)2, CuII and ZnII complexes showed a cathodic shift. In contrast, NiII and CoII complexes showed an anodic shift in the first ring reduction potential as compared to the corresponding MTPP(NO2)(CN)2.56 Trisubstituted MTPP(NO2)(CF3)2 (M = 2H, CoII, NiII, CuII, and ZnII), are readily reducible compared to related disubstituted porphyrins MTPP(CF3)2 (M = 2H, CoII, NiII, CuII, and ZnII) as reported in the literature,57 due to the presence of the nitro group. Among all the synthesized porphyrins, H2TPP(NO2)(CF3)2 has shown a lower HOMO–LUMO gap (1.51 V). A remarkable reduction in the HOMO–LUMO energy gap of 0.72 V, 0.43 V and 0.36 V was observed in H2TPP(NO2)(CF3)2 compared to H2TPP (2.23 V), H2TPP(NO2) (1.97 V) and H2TPP(NO2)Br2 (1.87 V), respectively.56

Intensity-dependent NLO studies

Investigating third-order nonlinear optical properties of different materials is essential for developing various nonlinear photonic device applications. When a high-intensity laser beam interacts with a material, the absorption and refraction coefficients of the materials change as functions of the intensity of the incident laser beam. The mathematical relationship that shows the variation in absorption and refraction coefficients with incident laser intensity is given by
 
α(I) = α0 + βI and n(I) = n0 + n2I(1)
where α0 and n0 are the linear absorption coefficient and refractive index of the material. Similarly, β, n2 and I are the third-order nonlinear two-photon absorption (TPA) coefficient, nonlinear refractive index and incident laser intensity. The single Gaussian beam-based Z-scan technique is the most effective method for obtaining the third-order nonlinear optical properties of a material.66 The single Gaussian beam Z-scan technique involves focusing a Gaussian laser beam on the sample using a convex lens. The laser beam that is transmitted through the sample is detected at each position as the sample is moved across the focal point. The nonlinear two-photon absorption coefficient is obtained using an open aperture (OA) Z-scan configuration in which the complete transmitted beam through the sample is collected using a photodetector. The nonlinear refraction property of the material is studied using the closed aperture (CA) Z-scan configuration, in which an aperture is placed before the collecting lenses. This straightforward single Gaussian beam Z-scan technique allows the estimation of the magnitude and sign of the third-order nonlinear coefficients, including the nonlinear refractive index (n2), nonlinear absorption coefficient (β), and nonlinear susceptibility (χ(3)).

The experimentally obtained OA and CA transmittance Z-scan curves can be theoretically fitted to estimate the third-order nonlinear optical coefficients of a material. For OA Z-scan data, the obtained transmittance curve can be fitted with the equation66–68

 
image file: d5dt00618j-t1.tif(2)
Here, β represents the 2PA coefficient, I is the incident laser intensity, and image file: d5dt00618j-t2.tif (L = sample length). Here, x = (z/zr), and the Rayleigh length (zr) signifies the effective sample length as image file: d5dt00618j-t3.tif, where ω0 (mm) is the beam waist at the focus point. Similarly, the nonlinear refraction phase shift of the material is estimated by fitting the experimentally obtained CA Z-scan data using the equation66–68
 
image file: d5dt00618j-t4.tif(3)
Here, Δϕ denotes the nonlinear phase shift, and Δφ is the nonlinear absorption phase shift, and the nonlinear refractive index n2 is obtained from the expression
 
image file: d5dt00618j-t5.tif(4)
in which λ is the excitation wavelength. The (χ(3)) value can also be obtained as per the following relationships: image file: d5dt00618j-t6.tif, and image file: d5dt00618j-t7.tif

In the present study, the third-order nonlinear optical properties of porphyrins were characterized using a single Gaussian beam femtosecond Z-scan technique. All the Z-scan measurements were performed using an 800 nm femtosecond (120 fs, 84 MHz) laser pulse with varying laser intensities.

Theoretically fitted intensity-dependent OA scan curves of all the porphyrins are shown in Fig. 4. The solid lines in Fig. 4 correspond to the theoretical fit using eqn (2). The OA curves of all samples at various intensities show a dip at the laser beam focal position, which clearly indicates the reverse saturable absorption (RSA) behaviour. The observed RSA behaviour can be attributed to the strong two-photon absorption due to the 800 nm wavelength laser excitation. As the intensity increases, there is a prominent increase in the RSA behaviour of all porphyrin samples. The extracted two-photon absorption coefficients of all the samples from the OA curves are shown in Fig. 5. An increasing trend of the two-photon absorption coefficient (β) was followed for all the porphyrins. However, all samples follow an increasing behaviour; H2TPP(NO2)(CF3)2 has the highest and NiTPP(NO2)(CF3)2 has the lowest TPA coefficient. The extracted nonlinear coefficients of all samples are tabulated in Table 3.


image file: d5dt00618j-f4.tif
Fig. 4 Intensity-dependent open aperture (OA) experimental Z-scan results of (a) H2TPP(NO2)(CF3)2, (b) CoTPP(NO2)(CF3)2, (c) NiTPP(NO2)(CF3)2, (d) CuTPP(NO2)(CF3)2, and (e) ZnTPP(NO2)(CF3)2. Laser parameters: 800 nm, 120 fs, and 84 MHz.

image file: d5dt00618j-f5.tif
Fig. 5 Nonlinear absorption coefficient (β) extracted from the intensity-dependent open aperture (OA) Z-scan results of (a) H2TPP(NO2)(CF3)2, (b) CoTPP(NO2)(CF3)2, (c) NiTPP(NO2)(CF3)2, (d) CuTPP(NO2)(CF3)2 and (e) ZnTPP(NO2)(CF3)2. Laser parameters: 800 nm, 120 fs, and 84 MHz. Error bars signify the typical experimental/fitting errors.
Table 3 Summary of the third-order nonlinear optical coefficients extracted from Z-scan studies of MTPP(NO2)(CF3)2 (M = 2H, CoII, NiII, CuII, and ZnII) porphyrins
Intensity (W m−2) (1012) β (m W−1) (× 10−10) Nonlinear refraction phase (Δϕ) Nonlinear absorption phase (Δφ) σ 2PA (GM) (× 106) n 2 (m2 W−1) (× 10−17) Real [χ(3)] (esu) (× 10−11) Im [χ(3)] (esu) (× 10−12) Total [χ(3)] (esu) (× 10−11)
H 2 TPP(NO 2 )(CF 3 ) 2
0.49 3.92 −1.52 0.05 0.81 −40.27 −31.36 19.46 31.43
0.97 6.11 −2.54 0.10 1.30 −33.59 −26.17 30.29 26.35
1.46 7.08 −3.11 0.12 1.46 −27.37 −21.32 35.14 21.61
1.95 8.10 −3.28 0.17 1.67 −21.68 −16.89 40.19 17.36
2.44 7.86 −3.27 0.23 1.62 −17.29 −13.47 38.99 14.03
2.92 7.48 −3.55 0.22 1.54 −15.66 −12.20 37.11 12.75
CoTPP(NO 2 )(CF 3 ) 2
3.41 0.35 −2.04 0.12 0.07 −7.70 −5.99 1.72 6.00
4.87 0.53 −2.62 0.10 0.11 −6.94 −5.40 2.62 5.41
7.30 0.96 −3.13 0.16 0.20 −5.52 −4.29 4.76 4.32
9.74 1.24 −3.21 0.26 0.26 −4.24 −3.30 6.13 3.36
14.60 1.34 −3.78 0.20 0.28 −3.33 −2.59 6.65 2.68
NiTPP(NO 2 )(CF 3 ) 2
14.60 0.04 −1.92 0.20 0.01 −1.69 −1.32 0.22 1.32
19.50 0.10 −2.46 0.26 0.02 −1.62 −1.27 0.48 1.27
24.35 0.15 −2.85 0.23 0.03 −1.50 −1.17 0.73 1.18
29.20 0.17 −2.94 0.24 0.04 −1.30 −1.01 0.84 1.01
34.10 0.21 −2.86 0.38 0.04 −1.08 −0.84 1.04 0.85
CuTPP(NO 2 )(CF 3 ) 2
4.87 — −1.05 0.08 — −2.78 −2.17 — —
9.74 0.09 −1.92 0.19 0.02 −2.54 −1.98 0.43 1.98
14.60 0.19 −2.81 0.16 0.04 −2.48 −1.93 0.95 1.93
19.50 0.33 −2.95 0.31 0.07 −1.94 −1.51 1.65 1.52
24.35 0.54 −3.00 0.30 0.11 −1.59 −1.24 2.67 1.26
29.20 0.54 — — 0.11 — — 2.70 —
ZnTPP(NO 2 )(CF 3 ) 2
3.41 — −1.64 0.06 — −6.17 −4.81 — —
4.87 0.32 −2.19 0.15 0.06 −5.79 −4.51 1.56 4.51
7.30 0.54 −2.83 0.16 0.11 −4.99 −3.89 2.68 3.90
9.74 0.76 −2.99 0.22 0.16 −3.96 −3.08 3.76 3.11
14.60 0.97 −3.07 0.31 0.20 −2.71 −2.11 4.83 2.16
19.50 0.98 — — 0.20 — — 4.89 —

The closed aperture (CA) Z-scan was performed by varying laser beam intensities in a similar range to open aperture data, and the theoretically fitted CA Z-scan data are shown in Fig. 6. The CA Z-scans exhibit a peak-valley structure, which indicates the self-defocusing negative nonlinear refraction behaviour of the sample. The nonlinearity of materials could stem from the electronic and non-electronic effects. The negative nonlinearity of materials is basically non-electronic nonlinearity, which is observed due to the thermal effects induced on the sample during light propagation through the medium. The observed negative nonlinear refraction behaviour is a consequence of the cumulative thermal effect, which enhances the thermal nonlinearity of porphyrin beyond its electronic nonlinearity. This effect is particularly evident due to the high-repetition rate laser pulses (84 MHz). The existence of nonlinear absorption and nonlinear refraction is responsible for the asymmetry observed in the CA scans. The experimental CA Z-scans are analysed by fitting them using eqn (3), which includes both the term for the nonlinear refraction phase (Δϕ) and the term for the nonlinear absorption phase (Δφ). The solid lines seen in Fig. 6 correspond to the theoretical fit derived from eqn (3).


image file: d5dt00618j-f6.tif
Fig. 6 Intensity-dependent closed aperture (CA) experimental Z-scan results of (a) H2TPP(NO2)(CF3)2, (b) CoTPP(NO2)(CF3)2, (c) NiTPP(NO2)(CF3)2, (d) CuTPP(NO2)(CF3)2 and (e) ZnTPP(NO2)(CF3)2. Laser parameters: 800 nm, 120 fs, and 84 MHz.

The nonlinear refractive indices of all the samples with different input laser intensities calculated using eqn (4) are plotted and shown in Fig. 7. The refractive index also shows an increasing behaviour with the laser intensity for all the samples. The highest negative nonlinear refractive index ((−) 40 × 10−17 m2 W−1) was obtained for H2TPP(NO2)(CF3)2 and NiTPP(NO2)(CF3)2 had the lowest value ((−) 1 × 10−17 m2 W−1).


image file: d5dt00618j-f7.tif
Fig. 7 Nonlinear refractive index (n2) extracted from the intensity-dependent closed aperture (CA) Z-scan results of (a) H2TPP(NO2)(CF3)2, (b) CoTPP(NO2)(CF3)2, (c) NiTPP(NO2)(CF3)2, (d) CuTPP(NO2)(CF3)2 and (e) ZnTPP(NO2)(CF3)2. Laser parameters: 800 nm, 120 fs, and 84 MHz. Error bars signify the typical experimental/fitting errors.

A relative assessment of the NLO parameters obtained in this study is conducted regarding those reported in the literature under picosecond (ps), nanosecond (ns), and femtosecond (fs) laser excitation conditions. Table 4 outlines the NLO parameters documented in the literature for porphyrins and related molecules. Bulbul et al.53,54 studied the third-order nonlinear (NLO) optical properties of highly substituted Ni(II) and meso-β monofused porphyrins. By using the Z-scan technique with excitation parameters of 800 nm, 120 fs, and 84 MHz, they successfully extracted the two-photon absorption coefficient ranges and the nonlinear refractive index ranges as tabulated in Table 4. Bao et al.69 studied the third-order NLO properties of asymmetric and symmetric porphyrin derivatives with excitation parameters 532 nm, 7 ns, and 10 Hz, and their results showed that the two-photon absorption coefficient ranges from 0.9 to 3.7 × 10−9 m W−1 and the nonlinear refractive index ranges from (−) 13.0 to 58.1 × 10−10 (esu). Li et al.70 documented 2D metal–pyridylporphyrinic framework films and explored their third-order NLO properties using a nanosecond region at a wavelength of 532 nm. They revealed good β and n2 values ranging from 5.1 to 57 × 10−7 m W−1 and (−) 6.5 to 92 × 10−14 m2 W−1, respectively. Yasin et al.35 designed π-expanded zinc porphyrins and explored their NLO properties by using 532 nm, 3 ns, and 10 Hz laser parameters. Their findings demonstrated β values ranging from 1.03 to 2.08 × 10−9 m W−1 and n2 values ranging from (−) 0.77 to 2.45 × 10−9 (esu). Garai et al.71 examined the NLO properties of trans-A2B-corroles in solution and aggregated states using 1064 nm, 250 fs, and 80 MHz laser parameters. Their results revealed that trans-A2B-corroles in an aggregated state showed higher β and n2 value ranges of 2.0–444 × 10−13 m W−1 and (−) 1.1–71.8 × 10−18 m2 W−1, respectively, compared to the trans-A2B-corroles in the solution state (β = 1.9–17.2 × 10−15 m W−1 and n2 = (−) 7.8–25.9 × 10−18 m2 W−1). Yadav et al.44 investigated push–pull trans-A2B-corroles and assessed their femtosecond third-order NLO properties using excitation parameters of 800 nm, 150 fs, and 80 MHz. Their findings demonstrated that the investigated corroles showed a negative type of nonlinearity and self-defocusing behaviour with the n2 value ranging from (−) 1.30 to 10.0 × 10−10 (esu). In comparison, the asymmetric β-trisubstituted electron-deficient synthesized porphyrins explored in the present study exhibited excellent NLO properties, comparable to the coefficients reported for porphyrins and related molecules in the literature. However, a few studies reported by other groups show one or two orders of magnitude higher than those found in this study.

Table 4 Summary of NLO data extracted from other porphyrins and related molecules
Porphyrins and their analogs Laser details β n 2 Total [χ(3)] (esu) Ref.
MTPP(NO2)(CF3)2 800 nm, 120 fs, 84 MHz 0.04–8.10 × 10−10 m W−1 (−) 1.08–40.27 × 10−17 m2 W−1 0.85–31.43 × 10−11 This work
meso-β monofused porphyrins 800 nm, 120 fs, 84 MHz 0.18–39.06 × 10−11 m W−1 (−) 0.5–5.28 × 10−16 m2 W−1 0.39–2.84 × 10−10 54
Highly substituted Ni(II) porphyrins 800 nm, 120 fs, 84 MHz 22–33 × 10−10 m W−1 (−) 4.14–16.30 × 10−15 m2 W−1 3.22–12.69 × 10−9 53
Asymmetric and symmetric porphyrin 532 nm, 7 ns, 10 Hz 0.9–3.7 × 10−9 m W−1 (−) 13.0–58.1 × 10−10 (esu) 4.2–17.9 × 10−11 69
2D metal-pyridylporphyrinic framework films 532 nm 5.1–57 × 10−7 m W−1 (−) 6.5–92 × 10−14 m2 W−1 3.91–54.3 × 10−8 70
trans-A2B-corroles in solution 1064 nm, 250 fs, 80 MHz 1.9–17.2 × 10−15 m W−1 (−) 7.8–25.9 × 10−18 m2 W−1 71
trans-A2B-corroles in the aggregated state 1064 nm, 250 fs, 80 MHz 2.0–444 × 10−13 m W−1 (−) 1.1–71.8 × 10−18 m2 W−1 71
trans-A2B-type cobalt corroles 532 nm, 4 ns, 10 Hz 1.05–1.45 × 10−11 m W−1 (−) 4.46–5.11 × 10−11 (esu) 6.46–7.75 × 10−12 72
Push–pull trans-A2B-corroles 800 nm, 150 fs, 80 MHz 0.65–6.80 × 10−10 m W−1 (−) 1.30–10.0 × 10−10 (esu) 0.31–2.40 × 10−9 44
Zinc porphyrin 532 nm, 3 ns, 10 Hz 1.03–2.08 × 10−9 m W−1 (−) 0.77–2.45 × 10−9 (esu) 35
Porphyrin-based polyimides 532 nm, 6 ns, 10 Hz 0.51–1.39 × 10−5 (esu) (−) 2.42 –10.26 × 10−10 (esu) 3.74–15.65 × 10−11 73
Porphyrin and polyoxometalate hybrids 532 nm, 6 ns, 10 Hz 0.65–2.53 × 10−5 (esu) (−) 0.80–1.56 × 10−9 (esu) 1.55–2.38 × 10−10 74
Polyoxometalate–porphyrin hybrids 532 nm, 6 ns, 10 Hz 0.39–2.16 × 10−5 (esu) (−) 0.54–1.65 × 10−9 (esu) 0.82–2.52 × 10−10 75
Keggin-type anions and porphyrins 532 nm, 6 ns, 10 Hz 2.08–15.58 × 10−6 (esu) (−) 1.86–12.45 × 10−10 (esu) 0.27–1.85 × 10−10 13
Zinc porphyrin and zinc phthalocyanine 680–1080 nm, 150 fs, 80 MHz (−) 0.5–9.0 × 10−15 m2 W−1 0.06–7.7 × 10−9 11
Porphyrin-POM composite films 532 nm, 7 ns, 10 Hz 0.05–0.45 × 10−5 (esu) (−) 0.12–2.12 × 10−10 (esu) 0.30–2.78 × 10−11 76
Porphyrin and polyoxometalate 532 nm, 7 ns, 10 Hz 1.31–1.50 × 10−5 (esu) (−) 1.74–2.22 × 10−10 (esu) 3.35–4.15 × 10−11 77
Porphyrin–Anderson type 532 nm, 6 ns, 10 Hz 0.23–14.84 × 10−5 (esu) (−) 1.34–16.80 × 10−10 (esu) 2.05–31.72 × 10−11 7
Polyoxometalate hybrid

Conclusions

A series of electron-deficient β-trisubstituted porphyrins H2TPP(NO2)(CF3)2 and their metal complexes MTPP(NO2)(CF3)2 (M = CoII, NiII, CuII and ZnII) have been synthesized in good yields and characterized spectroscopically and structurally. Single crystal X-ray analysis and DFT optimizations showed the saddle-shaped configuration of CoTPP(NO2)(CF3)2, NiTPP(NO2)(CF3)2 and CuTPP(NO2)(CF3)2. The synthesized MTPP(NO2)(CF3)2 exhibit a bathochromic shift in the Soret band and longest Q-band (Qx(0,0)) compared to their MTPPs, MTPP(NO2) and MTPP(NO2)Br2, which can be attributed to the strong electron-accepting effect of trifluoromethyl groups functionalized at the β-position and the nonplanar conformation of the synthesized porphyrins, demonstrated by the DFT calculations. The considerable downfield shift of NH resonance indicates the electronic effect of substituents and the synthesized porphyrins’ nonplanarity compared to H2TPP, H2TPP(NO2), and H2TPP(NO2)Br2. The first reduction potential of the synthesized porphyrins reveals that they are easier to reduce compared to similar reported macrocycles. A remarkable reduction in the HOMO–LUMO energy gap of 0.72 V, 0.43 V, and 0.36 V was observed in H2TPP(NO2)(CF3)2 (1.51 V) compared to H2TPP (2.23 V), H2TPP(NO2) (1.97 V) and H2TPP(NO2)Br2 (1.87 V), respectively. The synthesized porphyrins showed high ground state dipole moments ranging from 6.42 to 7.75 Debye. The nonlinear optical properties of the synthesized porphyrins were investigated in the visible region (800 nm) using a femtosecond Z-scan technique (120 fs, 84 MHz). H2TPP(NO2)(CF3)2 exhibits the highest two-photon absorption coefficient (β) and cross-section (σ2PA) among all the studied compounds, 8.10 × 10−10 m W−1 and 1.67 × 106 GM, respectively. These results suggest that the synthesized porphyrins hold the potential for advanced applications in photonic devices and other optoelectronic technologies.

Data availability

Data are available in the submitted article's ESI.†

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

The authors gratefully acknowledge the Science and Engineering Research Board (SERB/CRG/2020/005958) for financial support. Reena Jangra thanks the Ministry of Education (MoE), Govt. of India, for the senior research fellowship. The authors thank DST-FIST, New Delhi, for providing funds (SR/FST/CS-II/2018/72(C)) to purchase 500 MHz NMR and SCXRD instruments.

References

  1. Z. B. Qin, Y. Q. Wen, Y. L. Shang, Y. L. Song and Y. Z. Wan, Appl. Phys. A:Mater. Sci. Process., 2007, 87, 277–280 Search PubMed .
  2. F. Castet, V. Rodriguez, J. L. Pozzo, L. Ducasse, A. Plaquet and B. Champagne, Acc. Chem. Res., 2013, 46, 2656–2665 CrossRef CAS PubMed .
  3. R. Bano, M. Asghar, K. Ayub, T. Mahmood, J. Iqbal, S. Tabassum, R. Zakaria and M. A. Gilani, Front. Mater., 2021, 8, 1–24 Search PubMed .
  4. X. Han, L. Ding, Z. Tian, Y. Song, R. Xiong, C. Zhang, J. Han and S. Jiang, Int. J. Biol. Macromol., 2023, 224, 1236–1243 Search PubMed .
  5. K. Senthil, S. Kalainathan, A. R. Kumar and P. G. Aravindan, RSC Adv., 2014, 4, 56112–56127 Search PubMed .
  6. M. O. Senge, M. Fazekas, E. G. A. Notaras, W. J. Blau, M. Zawadzka, O. B. Locos and E. M. N. Mhuircheartaigh, Adv. Mater., 2007, 19, 2737–2774 CrossRef CAS .
  7. S. Ul Hassan, H. M. Asif, Y. Zhou, L. Zhang, N. Qu, J. Li and Z. Shi, J. Phys. Chem. C, 2016, 120, 27587–27599 CrossRef .
  8. B. Champagne, A. Plaquet, J. L. Pozzo, V. Rodriguez and F. Castet, J. Am. Chem. Soc., 2012, 134, 8101–8103 CrossRef CAS PubMed .
  9. B. P. Biswal, S. Valligatla, M. Wang, T. Banerjee, N. A. Saad, B. M. K. Mariserla, N. Chandrasekhar, D. Becker, M. Addicoat, I. Senkovska, R. Berger, D. N. Rao, S. Kaskel and X. Feng, Angew. Chem., Int. Ed., 2019, 58, 6896–6900 Search PubMed .
  10. Y. Zhai, J. Q. Yang, Y. Zhou, J. Y. Mao, Y. Ren, V. A. L. Roy and S. T. Han, Mater. Horiz., 2018, 5, 641–654 RSC .
  11. M. S. S. Bharati, S. Bhattacharya, J. V. S. Krishna, L. Giribabu and S. V. Rao, Opt. Laser Technol., 2018, 108, 418–425 CrossRef CAS .
  12. M. Samal, S. Valligatla, N. A. Saad, M. V. Rao, D. N. Rao, R. Sahu and B. P. Biswal, Chem. Commun., 2019, 55, 11025–11028 RSC .
  13. F. Khurum Shehzad, A. Iqbal, Y. Zhou, L. Zhang, T. Wang and X. Ren, J. Phys. Chem. C, 2020, 124, 9442–9450 Search PubMed .
  14. K. Kandasamy, S. J. Shetty, P. N. Puntambekar, T. S. Srivastava, T. Kundu and B. P. Singh, J. Porphyrins Phthalocyanines, 1999, 3, 81–86 Search PubMed .
  15. W. Blau, H. Byrne, W. M. Dennis and J. M. Kelly, Opt. Commun., 1985, 56, 25–29 Search PubMed .
  16. C. Ryppa, D. Niedzwiedzki, N. L. Morozowich, R. Srikanth, M. Zeller, H. A. Frank and C. Bruckner, Chem. – Eur. J., 2009, 15, 5749–5762 CrossRef CAS PubMed .
  17. J. Humphrey and D. Kuciauskas, J. Phys. Chem. B, 2004, 108, 12016–12023 CrossRef CAS .
  18. P. P. Kiran, D. R. Reddy, B. G. Maiya, A. K. Dharmadhikari, G. R. Kumar and D. N. Rao, Opt. Commun., 2005, 252, 150–161 CrossRef CAS .
  19. J. E. Reeve, H. A. Collins, K. De Mey, M. M. Kohl, K. J. Thorley, O. Paulsen, K. Clays and H. L. Anderson, J. Am. Chem. Soc., 2009, 131, 2758–2759 CrossRef CAS PubMed .
  20. T. Zhang, Y. Zhao, K. Song, I. Asselberghs, A. Persoons, K. Clays and M. J. Therien, Inorg. Chem., 2006, 45, 9703–9712 CrossRef CAS PubMed .
  21. X. Hu, D. Xiao, S. Keinan, I. Asselberghs, M. J. Therien, K. Clays, W. Yang and D. N. Beratan, J. Phys. Chem. C, 2010, 114, 2349–2359 CrossRef CAS .
  22. H. L. Anderson, Adv. Mater., 1994, 6, 834–836 CrossRef CAS .
  23. H. L. Anderson, S. J. Martin and D. D. C. Bradley, Angew. Chem., Int. Ed. Engl., 1994, 33, 655–657 CrossRef .
  24. T. E. O. Screen, J. R. G. Thorne, R. G. Denning, D. G. Bucknall and H. L. Anderson, J. Mater. Chem., 2003, 13, 2796–2808 Search PubMed .
  25. P. N. Taylor, A. P. Wylie, J. Huuskonen and H. L. Anderson, Angew. Chem., Int. Ed., 1998, 37, 986–989 CrossRef CAS PubMed .
  26. J. R. G. Thorne, S. M. Kuebler, R. G. Denning, I. M. Blake, P. N. Taylor and H. L. Anderson, Chem. Phys., 1999, 248, 181–193 CrossRef CAS .
  27. J. L. Sessler and D. Seidel, Angew. Chem., Int. Ed., 2003, 42, 5134–5175 Search PubMed .
  28. Z. S. Yoon, J. H. Kwon, M. C. Yoon, M. K. Koh, S. B. Noh, J. L. Sessler, J. T. Lee, D. Seidel, A. Aguilar, S. Shimizu, M. Suzuki, A. Osuka and D. Kim, J. Am. Chem. Soc., 2006, 128, 14128–14134 CrossRef CAS PubMed .
  29. A. Tsuda, A. Nakano, H. Furuta, H. Yamochi and A. Osuka, Angew. Chem., Int. Ed., 2000, 39, 558–561 Search PubMed .
  30. I. V. Rubtsov, K. Susumu, G. I. Rubtsov and M. J. Therien, J. Am. Chem. Soc., 2003, 125, 2687–2696 Search PubMed .
  31. Y. Matsuzaki, A. Nogami, A. Tsuda, A. Osuka and K. Tanaka, J. Phys. Chem. A, 2006, 110, 4888–4899 CrossRef CAS PubMed .
  32. Y. Matsuzaki, A. Nogami, Y. Iwaki, N. Ohta, N. Yoshida, N. Aratani, A. Osuka and K. Tanaka, J. Phys. Chem. A, 2005, 109, 703–713 CrossRef CAS PubMed .
  33. Z. B. Liu, Y. F. Xu, X. Y. Zhang, X. L. Zhang, Y. S. Chen and J. G. Tian, J. Phys. Chem. B, 2009, 113, 9681–9686 CrossRef CAS PubMed .
  34. R. Jangra and M. Sankar, J. Porphyrins Phthalocyanines, 2025, 29, 123–133 CrossRef CAS .
  35. A. Yasin, V. S. Nair, M. H. Ab Rahim, Y. Yamaoka, C. S. Yelleswarapu and R. Jose, J. Mater. Chem. C, 2021, 9, 17461–17470 RSC .
  36. K. S. Suslick, C. Chen, G. R. Meredith and L.-T. Cheng, J. Am. Chem. Soc., 1992, 114, 6928–6930 CrossRef CAS .
  37. T. Morotti, M. Pizzotti, R. Ugo, S. Quici, M. Bruschi, P. Mussini and S. Righetto, Eur. J. Inorg. Chem., 2006, 1743–1757 CrossRef CAS .
  38. K. J. McEwan, G. Bourhill, J. M. Robertson and H. L. Anderson, J. Nonlinear Opt. Phys. Mater., 2000, 9, 451–468 CrossRef CAS .
  39. P. T. Anusha, A. R. Thomas, R. Philip and S. V. Rao, Chem. Phys. Lett., 2015, 641, 23–28 Search PubMed .
  40. P. Liang, Y. Mi, J. Duan, Z. Yang, D. Wang, H. Cao, W. He and H. Yang, Chin. J. Chem., 2016, 34, 381–386 CrossRef CAS .
  41. T. Tanaka and A. Osuka, Chem. Soc. Rev., 2015, 44, 943–969 RSC .
  42. S. M. LeCours, H. W. Guan, S. G. DiMagno, C. H. Wang and M. J. Therien, J. Am. Chem. Soc., 1996, 118, 1497–1503 CrossRef .
  43. C. C. Yang, L. Li, W. Q. Tian, W. Q. Li and L. Yang, Phys. Chem. Chem. Phys., 2022, 24, 13275–13285 RSC .
  44. P. Yadav, T. Anand, S. S. B. Moram, S. Bhattacharya, M. Sankar and S. V. Rao, Dyes Pigm., 2017, 143, 324–330 CrossRef CAS .
  45. P. Rathi, Ekta, S. Kumar, D. Banerjee, V. R. Soma and M. Sankar, Dalton Trans., 2020, 49, 3198–3208 Search PubMed .
  46. S. Kumar, J. N. Acharyya, D. Banerjee, V. R. Soma, G. V. Prakash and M. Sankar, Dalton Trans., 2021, 50, 6256–6272 RSC .
  47. R. K. Rohal, M. Shanu, J. N. Acharyya, G. V. Prakash and M. Sankar, Dalton Trans., 2022, 51, 9049–9061 RSC .
  48. R. K. Rohal, J. N. Acharyya, M. Shanu, G. V. Prakash and M. Sankar, Inorg. Chem., 2022, 61, 1297–1307 CrossRef CAS PubMed .
  49. A. S. Bulbul, N. Chaudhri, M. Shanu, J. N. Acharyya, G. V. Prakash and M. Sankar, Inorg. Chem., 2022, 61, 9968–9982 CrossRef CAS PubMed .
  50. I. Yadav, M. Shanu, J. N. Acharyya, G. V. Prakash and M. Sankar, Inorg. Chem., 2022, 61, 19289–19301 CrossRef CAS PubMed .
  51. S. Kumari, I. Yadav, J. N. Acharyya, M. Shanu, G. V. Prakash and M. Sankar, Dyes Pigm., 2023, 217, 111416 CrossRef CAS .
  52. R. K. Rohal, D. Banerjee, N. Rana, V. R. Soma and M. Sankar, Dalton Trans., 2024, 53, 6436–6444 RSC .
  53. A. S. Bulbul, A. Kuriakose, R. Komal, J. N. Acharyya, G. V. Prakash and M. Sankar, Inorg. Chem., 2024, 63, 17967–17982 CrossRef CAS PubMed .
  54. A. S. Bulbul, R. Jangra, A. Kuriakose, N. J. Acharyya, G. V. Prakash and M. Sankar, Chem. – Eur. J., 2025, e202403473 CrossRef .
  55. A. S. Bulbul, J. Mogilipuri, V. R. Soma and M. Sankar, Dalton Trans., 2025, 54, 3679–3694 RSC .
  56. R. Kumar and M. Sankar, Inorg. Chem., 2014, 53, 12706–12719 CrossRef CAS PubMed .
  57. W. Arif and R. Kumar, ChemistrySelect, 2023, 8, e202304575 CrossRef CAS .
  58. Z. Zhou, Q. Liu, Z. Yan, G. Long, X. Zhang, C. Cao and R. Jiang, Org. Lett., 2013, 15, 606–609 CrossRef CAS PubMed .
  59. A. B. J. Parusel, T. Wondimagegn and A. Ghosh, J. Am. Chem. Soc., 2000, 122, 6371–6374 CrossRef CAS .
  60. S. G. DiMagno, A. K. Wertsching and C. R. Ross, J. Am. Chem. Soc., 1995, 117, 8279–8280 CrossRef CAS .
  61. A. G. Mojarrad and S. Zakavi, RSC Adv., 2016, 6, 100931–100938 RSC .
  62. V. V. Smirnov, E. K. Woller and S. G. DiMagno, Inorg. Chem., 1998, 37, 4971–4978 CrossRef CAS PubMed .
  63. C. J. Medforth and J. J. Smith, Tetrahedron Lett., 1990, 31, 5583–5586 CrossRef CAS .
  64. K. M. Kadish, X. Q. Lin and B. C. Han, Inorg. Chem., 1987, 26, 4161–4167 CrossRef CAS .
  65. K. M. Kadish, Z. Ou, X. Tan, T. Boschi, D. Monti, V. Fares and P. Tagliatesta, Dalton Trans., 1999, 25, 1595–1601 RSC .
  66. M. Sheik-Bahae, A. A. Said, T. H. Wei, D. J. Hagan and E. W. Van Stryland, IEEE J. Quantum Electron., 1990, 26, 760–769 CrossRef CAS .
  67. J. N. Acharyya, D. N. Rao, M. Adnan, C. Raghavendar, R. B. Gangineni and G. V. Prakash, Adv. Mater. Interfaces, 2020, 7, 2000035 CrossRef CAS .
  68. M. Priyadarshini, J. N. Acharyya, S. Mahajan and G. V. Prakash, Opt. Laser Technol., 2021, 139, 107008 CrossRef CAS .
  69. C. Bao, Y. Li, Y. Li, Z. Si, Y. Zhang, C. Chen, L. Wang and Q. Duan, New J. Chem., 2021, 45, 16030–16038 RSC .
  70. D. J. Li, Q. H. Li, Z. G. Gu and J. Zhang, Nano Lett., 2021, 21, 10012–10018 CrossRef CAS PubMed .
  71. A. Garai, S. Kumar, W. Sinha, C. S. Purohit, R. Das and S. Kar, RSC Adv., 2015, 5, 28643–28651 RSC .
  72. G. Lu, P. Zhang, Y. Fang, Y. Gao and Q. Hu, New J. Chem., 2021, 45, 2103–2109 RSC .
  73. F. K. Shehzad, Q. U. Khan, Q. Mahmood, F. Ghafoor, H. O. Alsaab, S. A. A. Shah, N. Athir and A. Iqbal, Opt. Mater., 2022, 127, 112317 CrossRef CAS .
  74. T. Akhtar, U. Saleem, H. K. Thabet, F. K. Shehzad, K. Mehmood, A. Iqbal, H. M. Asif, Z. M. El-Bahy, H. I. A. Qazi and M. Sohail, Spectrochim. Acta, Part A, 2024, 319, 124551 CrossRef CAS PubMed .
  75. H. M. Asif, A. Iqbal, Y. Zhou, L. Zhang, T. Wang, M. I. U. Farooqi and R. Sun, Dyes Pigm., 2021, 184, 108758 CrossRef CAS .
  76. Z. Shi, Y. Zhou, L. Zhang, D. Yang, C. Mu, H. Ren, F. K. Shehzad and J. Li, Dalton Trans., 2015, 44, 4102–4107 RSC .
  77. Z. Shi, Y. Zhou, L. Zhang, C. Mu, H. Ren, D. U. Hassan, D. Yang and H. M. Asif, RSC Adv., 2014, 4, 50277–50284 RSC .

Footnotes

† Electronic supplementary information (ESI) available. CCDC 2389047–2389049. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5dt00618j
‡ These authors contributed equally.
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