A rigid xanthene–anthracene-based scaffold exhibiting ultra deep blue emission: multifunctional material as emitter and host for blue OLEDs

Abstract

Ultra-deep blue fluorescent emitters with Commission Internationale de L’Eclairage (CIE_y) < 0.08 are still in demand for achieving vibrant full-color displays. Herein, we have synthesized xanthene–anthracene-based 14-(4-(10-phenylanthracen-9-yl)phenyl)-14H-dibenzo[a,j]xanthene (PhAn-Xn), in which xanthene and anthracene are linked by an orthogonal phenyl bridge to prevent aggregation-induced quenching. PhAn-Xn exhibits an emission maximum at 430 nm, with a full width at half maximum (FWHM) of 48 nm, and a prompt lifetime of 0.7 ns. Using neat PhAn-Xn as the emitting material, an organic light-emitting diode (OLED) device was fabricated, achieving a maximum external quantum efficiency (EQE_max) of 4.2%, with CIE coordinates of (0.16, 0.06) at 8 V, following European Broadcasting Union standards, and a maximum luminance (L_max) of 4110 cd m⁻² (at 16.5 V). The device maintains an EQE of 4.0% at 1000 cd m⁻², retaining 95% of its maximum efficiency. PhAn-Xn, which exhibits superior charge transport properties to those of the widely used blue host bis[2-(diphenylphosphino)phenyl]ether oxide, was used as the host material in OLED devices employing the well-known blue dopant 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi). The PhAn-Xn-based device exhibits an electroluminescence maximum at 455 nm, consistent with the photoluminescence maximum of BCzVBi. An EQE_max of 6.5% was achieved, along with a maximum brightness of 41 557 cd m⁻² (at 16 V). The device maintains an EQE of 6.4%, retaining 98% of its maximum efficiency at 1000 cd m⁻². These results indicate that PhAn-Xn has multifunctionality and can serve as either an emitter or a host for deep blue OLEDs.

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1. Introduction

Organic light-emitting diode (OLED) technology has replaced conventional backlit flat-panel liquid crystal displays due to its higher contrast ratio, faster response time, thin profile, and wide viewing angle.^1–3 To achieve full-color displays, three primary RGB luminescent materials are needed, simultaneously possessing high efficiency and chromatic purity.^4,5 While green and red emitting materials have achieved impressive electroluminescence (EL) properties, deep-blue emitters still encounter significant challenges, including a trade-off between efficiency and chromatic purity.^6,7 In addition to high efficiency, chromatic purity is crucial for display applications. Although phosphorescent and thermally activated delayed fluorescence (TADF) materials can harvest 100% excitons via singlet–triplet conversion through intersystem crossing and what has come to be fallaciously referred to as reverse intersystem crossing, they generally suffer from emission broadening by 50–100 nm due to the charge-transfer nature of the excited state and the need for host materials to suppress emission quenching. These constraints limit the broader application of TADF emitters in commercially viable OLEDs.^8–10 However, fluorescent molecules, characterized by locally excited (LE) states, typically exhibit high chromatic purity, with a full-width at half maximum (FWHM) of less than 50 nm; therefore, conventional blue fluorescent materials continue to be employed in the industry. For blue emitters employed for OLED television displays, the National Television Standards Committee (NTSC) specifies Commission Internationale de L’Eclairage (CIE) color coordinates of (0.14, 0.08), while the European Broadcasting Union (EBU) Standards require CIE coordinates of (0.15, 0.06).^11–17 Therefore, there is an urgent need to develop blue emissive fluorophores with good color purity and CIE_y < 0.08 for achieving optimized full-color displays.

Two major concerns that need to be addressed simultaneously in deep-blue fluorescent OLEDs are mitigating aggregation-induced quenching (AIQ) in the emissive layer (EML) and ensuring high device performance at practical brightness levels. Woo et al. demonstrated a spiroacridine-triazine-based emitter in a 1,3-bis(N-carbazolyl)benzene (mCP) host, achieving a maximum external quantum efficiency (EQE_max) of 7.8% (FWHM = 68 nm), with maximum luminance (L_max) < 1000 cd m⁻² and CIE coordinates of (0.15, 0.08).¹⁸ Tagare et al. demonstrated triphenylamine-imidazole-based blue fluorophores in a 4,4′-bis(9-carbazolyl)-1,1′-biphenyl (CBP) host exhibiting an EQE_max of 3.2%, with an L_max of 1117 cd m⁻² and CIE coordinates of (0.16, 0.10).¹⁹ Recently, Tannir et al. demonstrated a benzobisoxazole-based fluorescent emitter (i.e. AB3Cz) functionalised by adamantane at the 2,6-position and carbazole at the 4,8-position in a mixed host system exhibiting an EQE_max of 1.1%, with an L_max of 294 cd m⁻² and CIE coordinates of (0.17, 0.08).²⁰ Several other reports also highlight challenges with blue OLEDs, as they either suffer from poor brightness or rely on host materials in the EML, which complicates device fabrication.^21,22 Although there are reports of neat EMLs in OLEDs, they suffer from severe efficiency roll-off as well as poor brightness,^23–26 limiting their practicality. To commercialize blue OLEDs, it is essential to identify appropriate molecular structures that can minimize intermolecular interactions while simultaneously improving brightness and reducing efficiency roll-off. Therefore, the development of blue-emitting materials capable of mitigating AIQ and eliminating the need for a host material in the EML is crucial for achieving deep-blue OLEDs.

In this work, we have synthesized xanthene–anthracene-based 14-(4-(10-phenylanthracen-9-yl)phenyl)-14H-dibenzo[a,j]xanthene (PhAn-Xn), which features xanthene and anthracene units linked by an orthogonal phenyl bridge to enhance twisting in the molecular structure. PhAn-Xn exhibits a structured emission maximum at 430 nm (FWHM = 48 nm). OLED devices were fabricated using neat PhAn-Xn as the EML, exhibiting an EQE_max of 4.2% and an L_max of 4110 cd m⁻² (at 16.5 V). The device retains 95% of the maximum efficiency at 1000 cd m⁻², with CIE coordinates of (0.16, 0.06) at 8 V following EBU standards. The significant overlap between the absorbance spectra of the well-known blue dopant 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi) and the emission spectra of PhAn-Xn implies that PhAn-Xn can efficiently transfer energy to BCzVBi, functioning as the host material. By employing 5 wt% BCzVBi:PhAn-Xn as the EML, an OLED was fabricated, which exhibited structured emission at 455 nm, similar to the PL spectra of the doped film. An EQE_max of 6.5% was achieved, along with an L_max of 41 557 cd m⁻² (at 16 V). The device retains 98% of its maximum efficiency at 1000 and 3000 cd m⁻². Hence, PhAn-Xn serves as a multifunctional material, exhibiting ultra-deep blue emission with CIE_y = 0.06 and improved efficiency roll-off, serving either as an emitter or as a host for deep-blue OLEDs.

2. Results and discussion

2.1. Materials design and synthetic procedure

Anthracene derivatives are widely employed as building blocks for blue-emitting materials due to their exceptional stability, photoluminescence quantum yield (PLQY), and electrical properties.²⁴ Additionally, 14H-dibenzo[a,j]xanthene serves as a rigid scaffold that suppresses non-radiative decay pathways, thereby enhancing the PLQY. Its bulky framework also hinders π–π stacking interactions in the aggregated state. The incorporation of a phenyl spacer group interrupts the π-conjugation between anthracene and the 14H-dibenzo[a,j]xanthene unit, thereby reducing the electronic coupling. The localisation of excitation on the anthracene unit results in narrow-band fluorescence. The synthetic route of PhAn-Xn is illustrated in Scheme 1. The condensation reaction of 4-bromobenzaldehyde with 2-naphthol in the presence of p-toluenesulfonic acid (pTSA),^27,28 followed by Suzuki–Miyaura coupling with (10-phenylanthracen-9-yl)boronic acid, results in the formation of PhAn-Xn. The final compound was purified by temperature gradient high vacuum sublimation and characterized by ¹H and ¹³C NMR spectroscopy (see Fig. S10 and S11, SI), as well as high-resolution mass spectrometry. The detailed synthetic procedure is provided in the SI.

Scheme 1 Synthetic route of PhAn-Xn.

2.2. Single-crystal XRD

Single crystals of PhAn-Xn were obtained by temperature gradient high vacuum sublimation. The ORTEP diagram of PhAn-Xn with 50% ellipsoid is shown in Fig. S1, SI, and the data are summarized in Table S1. PhAn-Xn adopts a highly twisted conformation as illustrated in Fig. 1a, with dihedral angles of 70° and 86° between the anthracene and the phenyl rings at 9- and 10-positions. Additionally, a larger dihedral angle of 90° is observed between the phenyl ring and the dibenzoxanthene unit. As depicted in Fig. 1b, the twisted structure of PhAn-Xn leads to the head-to-tail alignment of PhAn-Xn molecules in the solid-state packing, demonstrating weak C–H⋯π interactions at distances of 3.316, 3.208, and 2.621 Å. The suppression of intermolecular anthracene π–π interactions in the aggregated state may enhance solid-state emission efficiency in the neat film.

Fig. 1 (a) Structure of the isolated molecule, (b) C–H⋯π interactions in the unit cell, and (c) frontier molecular orbitals of PhAn-Xn employing the B3LYP-6-311G(d,p) basis set.

2.3. Theoretical investigations

To gain further insights into the electronic structure and structure–property relationship, theoretical calculations were performed using density functional theory (DFT) with the B3LYP-6-311G(d,p) basis set.^29–32 The optimized crystal structure (shown in Fig. 1a) reveals a highly twisted conformation (dihedral angle of ∼90°) due to orthogonal phenyl groups. PhAn-Xn exhibits a highest occupied molecular orbital (HOMO) energy of −5.26 eV, predominantly localized on the anthracene moiety. The lowest unoccupied molecular orbital (LUMO), also primarily concentrated on the anthracene unit, has an energy level of −1.78 eV, as illustrated in Fig. 1c, predicting the locally excited (LE) nature of the electronic transition.

2.4. Thermal characterization and frontier molecular orbital analysis

To investigate the thermal stability of the material, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed, as shown in Fig. S3, SI. The compound demonstrates a thermal decomposition temperature (T_d) of 421 °C (corresponding to 5% weight loss). No glass transition temperature (T_g) and melting point (T_m) were detected up to 300 °C. The high decomposition and glass transition temperatures indicate that the molecular morphology remains stable even at higher temperatures, confirming its suitability for vacuum deposition.

Ultraviolet photoelectron spectroscopy (UPS) was employed to determine the work function (Φ) and, subsequently, the HOMO energy level of a 50 nm PhAn-Xn neat film, as shown in Fig. S4 and S5, SI, using the following equation:³³

Φ = hv − (E_Fermi − E_cutoff),

where hv is the photon energy (21.22 eV for He I radiation), E_Fermi is the kinetic energy of the highest energy electron (Fermi edge), and E_cutoff is the kinetic energy at the secondary electron cut-off.

For PhAn-Xn, a HOMO energy of −5.07 eV was obtained, and the UV-visible absorption spectrum of a 50 nm PhAn-Xn neat film was used to calculate the energy band gap (E_g) of 2.96 eV, as shown in Fig. S4, SI. Subsequently, a LUMO energy of −2.11 eV was estimated using the relation: LUMO = E_g + HOMO.

2.5. Photophysical studies

The photophysical properties were investigated using UV-visible absorption and PL spectra in 10 µM toluene, as shown in Fig. 2a (summarised in Table 1). The absorption spectra in toluene display prominent vibrational bands ranging from 336 to 397 nm, attributed to the π–π* transition of the anthracene moiety.^34,35 PhAn-Xn displays a structured emission maximum at 415 nm, with an FWHM of 48 nm. A solvatochromic study of both the absorption and emission spectra shows a minimal spectral shift, as shown in Fig. S6, SI. On increasing the solvent polarity from toluene (Tol) to dichloromethane (DCM), there is a negligible shift in the absorption and emission maxima, confirming the LE nature of the S₁ state. The emission maximum of PhAn-Xn in the neat film was measured to be 430 nm, maintaining an FWHM of 48 nm. The slight bathochromic shift in the emission maximum (∼15 nm) of the neat film compared to the solution is attributed to the intermolecular delocalisation of PhAn-Xn in the solid state.³⁶ The twisted molecular structure hinders AIQ in the solid state.

Fig. 2 (a) Absorbance and fluorescence spectra in 10 µM toluene and neat film (the inset shows the photograph of 10 µM toluene under a 365 nm UV lamp) and (b) transient PL decay of PhAn-Xn in neat film.

Table 1 Key photophysical parameters of PhAn-Xn

Compound	λabs^a (nm)	λPL^b (nm) (soln/film)	ϕPL^c (%) (soln)	τP^d (ns) (film)	HOMO/LUMO^e (eV)	Td^f (°C)
a Absorbance maxima.b Fluorescence maximum.c Photoluminescence quantum yield (PLQY).d Prompt lifetime.e HOMO energy level was obtained from ultraviolet photoelectron spectroscopy (UPS) using He I radiation, whereas LUMO energy was estimated by adding optical band gap (Eg) and the HOMO energy.f Thermal decomposition temperature (Td) at 5% weight loss under a N2 atmosphere.
PhAn-Xn	336, 356, 376, 397	415/430	77	0.7	−5.07/−2.11	421

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To gain further insight into excited-state properties, transient PL decay was measured for PhAn-Xn in the neat film, with a prompt lifetime (corresponding to the S₁ → S₀ transition) of 0.7 ns, as shown in Fig. 2b. The short prompt lifetime facilitates rapid radiative deactivation of excitons, thereby minimizing non-radiative losses. The absence of spectral changes under air and vacuum implies no involvement of triplet excitons. No delayed component was detected, implying that PhAn-Xn functions as a conventional fluorescent emitter.

2.6. Electroluminescence properties

2.6.1. PhAn-Xn as an emitter. To evaluate the EL properties of PhAn-Xn, vacuum-deposited OLEDs were fabricated by adopting the following architecture: indium tin oxide (ITO)/NPB (80 nm)/PhAn-Xn (30 nm)/TPBi (50 nm)/LiF (1 nm)/Al (100 nm), where N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) and lithium fluoride (LiF) serve as the hole- and electron-injection layers; 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) functions as the electron transport layer and PhAn-Xn serves as the EML of the device (shown in Fig. 3).

Fig. 3 (a) Device architecture and molecular structure of the materials, (b) current density–voltage–luminance (J–V–L) characteristics, (c) EQE–luminance characteristics (inset shows the electroluminescence (EL) spectra by taking PhAn-Xn as the emissive layer (EML) and the chromaticity diagram at 8 V).

The current density–voltage–luminance (J–V–L) characteristics, EQE versus luminance curves, and the EL spectra of the device are shown in Fig. 3. Similar to the PL spectrum in neat film, PhAn-Xn displays narrow deep-blue emission (FWHM of 50 nm) at 432 nm with CIE coordinates of (0.16, 0.06). The device achieves an EQE_max of 4.2%, an L_max of 4110 cd m⁻², a maximum power efficiency (PE_max) of 0.9 lm W⁻¹, and a maximum current efficiency (CE_max) of 1.9 cd A⁻¹. Additionally, the device maintains an EQE of 4.0%, retaining 95% of its maximum efficiency, at 1000 cd m⁻², and an EQE of 3.2%, retaining 76%, at 3000 cd m⁻². The improved efficiency roll-off and high luminance surpass those of previously reported deep-blue fluorescent and TADF emitters, which are not suitable for non-doped architectures (summarised in Table 2 and Table S2, SI).^{9,20,23,24,26,34,37–41} The asymmetric structure regulates electronic properties by varying dipoles and reduces intermolecular interactions by minimizing molecular stacking.

Table 2 Summary of the EL performances of deep-blue neat OLEDs with CIE_y ≤ 0.10

	Emitter	Lmax^a (cd m^−2)	EQE^a (max/1000)	CIE^a (x, y)	λEL^a (nm)	FWHM^a (nm)	Ref.
NA = not applicable.a Lmax = maximum luminance, EQE (max/1000) = maximum external quantum efficiency, and at 1000 cd m^−2, CIE = Commission Internationale de l’Eclairage coordinates, λEL = electroluminescence maximum, FWHM = full width at half maximum.b The approximate values calculated (- indicates that the calculation is not possible with existing data).
Neat	PhAn-Xn	4110	4.2/4.0	(0.15, 0.06)	432	50	This work
Fl	PIPD-MP-IMDB	1098	3.6/2.2^b	(0.15, 0.10)	434	66	26
	PIPD-MP-DPAC	1617	1.9/1.1^b	(0.16, 0.09)	418	61
	PIPD-MP-DPA	4158	4.4/3.5^b	(0.15, 0.08)	428	56
	m-PO-ABN	∼5500^b	5.9/-	(0.14, 0.10)	448	∼65^b	36
	TPAXAN	∼890^b	4.6/NA	(0.16, 0.04)	428	49	24
	MADN	∼390^b	3.0/NA	(0.15, 0.06)	434	52
	mPAC	3995	6.8/3.5	(0.16, 0.09)	448	56	42
TADF	PDT-1	787	3.9/NA	(0.15, 0.08)	434	∼80^b	39
	PDT-2	993	5.3/NA	(0.15, 0.09)	436	∼80^b

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2.6.2. PhAn-Xn as a host material. To elucidate the potential of PhAn-Xn as a host material, the well-known blue dopant BCzVBi was used. The significant overlap between the absorbance spectra of BCzVBi and the emission spectra of PhAn-Xn (shown in Fig. S7, SI) suggests that PhAn-Xn can efficiently transfer energy to BCzVBi, making it a suitable host material. The emission maximum in 5 wt% BCzVBi:PhAn-Xn was observed at 444 nm (structured emission corresponding to BCzVBi only), confirming that PhAn-Xn efficiently transfers energy to BCzVBi. The transient PL lifetime was measured to be 0.9 ns.

Bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO) has emerged as the most popular host for blue emitters in recent years, showcasing high EQE_max attributed to its high polarity.^43–50 However, DPEPO contains phosphine oxide moieties, which make it more susceptible to degradation.^51–53 Moreover, DPEPO has a very large band gap and poor hole-transporting ability, resulting in high driving voltage.⁵⁴ To evaluate the charge-transport properties of PhAn-Xn, a hole-only device (HOD) and an electron-only device (EOD) were fabricated and compared with the well-known DPEPO host (with predominantly good electron-transporting capability). The HOD structure was ITO/TAPC (20 nm)/host (80 nm)/TAPC (20 nm)/Al, whereas the EOD structure was ITO/TPBi (20 nm)/host (80 nm)/TPBi (20 nm)/Liq (2 nm)/Al, where 4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) and TPBi served as the hole-transport and electron-transport materials. Lithium 8-hydroxyquinolinolate (Liq) was used to lower the work function of Al, enhancing charge injection. To prevent charge-transport current from adjacent layers, the host layer was made thicker than the surrounding layers. The J–V characteristics of single-carrier devices are shown in Fig. 4. Owing to the higher current density (J) in the EOD compared to the HOD, PhAn-Xn exhibits predominantly electron-transporting properties, similar to DPEPO. However, PhAn-Xn exhibits better hole and electron transport abilities than DPEPO. These findings demonstrate that PhAn-Xn exhibits bipolar charge-transporting ability, leading to improved charge balance in OLEDs compared to DPEPO.

Fig. 4 J–V characteristics for the electron-only device (EOD) and the hole-only device (HOD) of PhAn-Xn and DPEPO.

Inspired by the remarkable charge-carrier properties of PhAn-Xn compared to DPEPO, vacuum-deposited devices were fabricated to further explore the EL performance with the following architecture: ITO/NPB (30 nm)/TCTA (20 nm)/5 wt% BCzVBi:host (30 nm)/TPBi (50 nm)/LiF (1 nm)/Al (100 nm), where NPB and LiF served as the hole- and electron-injection layers, 4,4′,4″-tris(carbazole-9-yl)triphenylamine (TCTA) as the hole-transport layer and TPBi as the electron transport layer. BCzVBi served as the blue dopant, while PhAn-Xn and DPEPO acted as the host in the EML (shown in Fig. 5).

Fig. 5 (a) Device architecture employing PhAn-Xn as the host material. (b) Device architecture employing DPEPO as the host material (the HOMO and LUMO energies stated correspond to neat materials, assuming that the energies do not change in blends). (c) Molecular structures of the materials. (d) Current density–voltage–luminance (J–V–L) characteristics. (e) EQE–luminance characteristics (inset show the electroluminescence (EL) spectra). (f) Chromaticity diagrams (at 8 V) for 5 wt% BCzVBi:PhAn-Xn and 5 wt% BCzVBi:DPEPO as the emissive layers (EMLs).

The J–V–L characteristics, EQE versus luminance curves, and the EL spectra of the device are presented in Fig. 5. On employing PhAn-Xn as the host, the EL spectra exhibit a structured peak at 455 nm (FWHM of 71 nm), which is slightly red-shifted compared to the PL spectrum. However, on employing DPEPO as the host, the EL maximum is further shifted to 496 nm (FWHM of 109 nm), attributed to the higher polarity of DPEPO compared to PhAn-Xn. The PhAn-Xn-based device achieves a high EQE_max of 6.5%, a PE_max of 5.6 lm W⁻¹, and a CE_max of 10.3 cd A⁻¹. The L_max reaches 41 557 cd m⁻² at 16 V. In contrast, the DPEPO-based device exhibits a low EQE_max of 1.9%, a PE_max of 8.1 lm W⁻¹, and a CE_max of 10.4 cd A⁻¹. The L_max reaches 17 379 cd m⁻² at 16.5 V, as summarised in Table 3. Additionally, the PhAn-Xn-based device exhibits improved efficiency roll-off, maintaining a constant EQE of 6.4% at 1000 cd m⁻² and even 3000 cd m⁻² compared to DPEPO.^55–58 Hence, PhAn-Xn serves as a suitable host material for blue emitters, maintaining improved efficiency roll-off and L_max (summarized in Table S3, SI). The current efficiency–luminance–power efficiency (CE–L–PE) characteristics of PhAn-Xn as an emitter and a host are shown in Fig. S8, SI. On increasing the voltage (6 V to 12 V), there is no residual emission even at higher voltages, signifying that the recombination is occurring solely in the EML (shown in Fig. S9, SI). Hence, PhAn-Xn functions as a multifunctional material, exhibiting ultra-deep-blue emission and balanced charge transport, making it an excellent host for blue OLEDs with improved EL properties.

Table 3 Electroluminescence properties of neat PhAn-Xn, 5 wt% BCzVBi:PhAn-Xn, and 5 wt% BCzVBi:DPEPO

Emitter	λEL^a (nm)	Lmax^b (cd m^−2)	EQE^c (%) (max/1000/3000)	CEmax^d (cd A^−1)	PEmax^e (lm W^−1)	FWHM^f	CIE^g (x, y)
a Electroluminescence maximum.b Maximum luminance.c Maximum external quantum efficiency/at 1000 cd m^−2/at 3000 cd m^−2.d Maximum current efficiency.e Maximum power efficiency.f Full width at half maximum.g The Commission Internationale de L’Eclairage (CIE) coordinates at 8 V.
PhAn-Xn	432	4110	4.2/4.0/3.2	1.9	0.9	50	(0.15, 0.06)
BCzVBi:PhAn-Xn	455	41 557	6.5/6.4/6.4	10.3	5.6	71	(0.15, 0.20)
BCzVBi:DPEPO	496	17 379	1.9/1.1/1.0	10.4	8.1	109	(0.21, 0.39)

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3. Conclusion

In summary, we have designed and synthesized a deep-blue fluorescent emitter, PhAn-Xn, in which xanthene and anthracene moieties are connected by an orthogonal phenyl linker. A structured narrow emission spectrum peaking at 430 nm (FWHM = 48 nm) is obtained, indicating the LE nature of the S₁ state and a prompt lifetime of 0.7 ns. In the neat PhAn-Xn OLED device, an EL maximum of 432 nm, an EQE_max of 4.2%, and an L_max of 4110 cd m⁻² were achieved. The device maintains an EQE of 4.0% at 1000 cd m⁻², retaining 95% of its maximum efficiency. The obtained CIE coordinates of (0.16, 0.06) rank among the best results reported so far, matching well with the NTSC and EBU standards for standard deep-blue fluorescent OLEDs. PhAn-Xn exhibits superior charge-transport properties (both electron and hole) compared to DPEPO, highlighting its significance as a host material. By employing PhAn-Xn and DPEPO as hosts, OLEDs were fabricated using the well-known blue dopant BCzVBi. The PhAn-Xn-based device exhibited structured emission peaks at 455 nm, an EQE_max of 6.5%, and an L_max of 41 557 cd m⁻². The device maintained an EQE of 6.4%, retaining 98% of its maximum efficiency at 1000 cd m⁻². These results demonstrate that PhAn-Xn is a multifunctional material, capable of producing deep blue emission with CIE coordinates of (0.16, 0.06) and improved efficiency roll-off, while also serving as an effective host for blue OLEDs.

Conflicts of interest

There are no conflicts of interest to declare.

Data availability

The data are provided within the main text and in the supporting information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d5tc02452h.

CCDC 2410935 contains the supplementary crystallographic data for this paper.⁵⁹

Acknowledgements

The authors are extremely grateful to the Department of Science and Technology (DSTFIST: SR/FST/PSII009/2010) for providing access to the instrumental facility at MRC, IISc Bangalore. The authors thank Indian Science Technology and Engineering Facilities Map (I-STEM), a Program supported by the Office of the Principal Scientific Adviser to the Govt. of India, for providing access to the SC-XRD facility (Bruker LT D8 Quest) at Indian Institute of Science, Bangalore to carry out this work. The authors also thank INF, IISc Bangalore for providing access to the NMR facility. N. Y. thanks IISc for the doctoral fellowship. P. R. thanks IISc and the Ministry of Human Resource Development (MHRD), India (Grant No. MoE-STARS/STARS-2/2023-0651), the India–Taiwan Programme of Cooperation in Science and Technology (Grant No. 2024/IN-TW/07), and the Science & Engineering Research Board (SERB), India for the SERB-Power Grant (SPG) (Grant No. SPG/2020/000107) for the financial support.

References

1. K. Müllen and U. Scherf, Organic light emitting devices: synthesis, properties and applications, John Wiley & Sons, 2006.
2. H. Yersin, Highly efficient OLEDs with phosphorescent materials, John Wiley & Sons, 2008.
3. T. Chatterjee and K. T. Wong, Adv. Opt. Mater., 2019, 7, 1800565.
4. P. E. Burrows, G. Gu, V. Bulovic, Z. Shen, S. R. Forrest and M. E. Thompson, IEEE Trans. Electron Devices, 1997, 44, 1188–1203.
5. S. Kumar, D. Kumar, Y. Patil and S. Patil, J. Mater. Chem. C, 2015, 4, 193–200.
6. H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi, Nature, 2012, 492, 234–238.
7. D. Zhang, M. Cai, Z. Bin, Y. Zhang and D. Zhang, Chem. Sci., 2016, 7, 3355–3363.
8. Z. Yang, Z. Mao, Z. Xie, Y. Zhang, S. Liu, J. Zhao and J. Zhao, Chem. Soc. Rev., 2017, 46, 915–1016.
9. J. W. Sun, J. Y. Baek, K. H. Kim, J. S. Huh, S. K. Kwon, Y. H. Kim and J. J. Kim, J. Mater. Chem. C, 2017, 5, 1027–1032.
10. Z. Li, W. Li, C. Keum, E. Archer, B. Zhao, A. M. Z. Slawin, W. Huang, M. C. Gather, I. D. W. Samuel and E. Zysman-Colman, J. Phys. Chem. C, 2019, 123, 24772–24785.
11. S. Tang, M. Liu, P. Lu, H. Xia, M. Li, Z. Xie, F. Shen, C. Gu, H. Wang, B. Yang and Y. Ma, Adv. Funct. Mater., 2007, 17, 2869–2877.
12. Z. Gao, Y. Liu, Z. Wang, F. Shen, H. Liu, G. Sun, L. Yao, Y. Lv, P. Lu and Y. Ma, Chem. – Eur. J., 2013, 19, 2602–2605.
13. K. Goushi, K. Yoshida, K. Sato and C. Adachi, Nat. Photonics, 2012, 6, 253–258.
14. S. Reineke and M. A. Baldo, Phys. Status Solidi A, 2012, 209, 2341–2353.
15. J. Tagare, D. K. Dubey, J. H. Jou and S. Vaidyanathan, Dyes Pigm., 2019, 160, 944–956.
16. X. H. Zhu, J. Peng, Y. Cao and J. Roncali, Chem. Soc. Rev., 2011, 40, 3509–3524.
17. M. Zhu and C. Yang, Chem. Soc. Rev., 2013, 42, 4963–4976.
18. S. Woo, Y. Kim, M. Kim, J. Y. Baek, S. Kwon, Y. Kim and J. Kim, Chem. Mater., 2018, 30, 857–863.
19. J. Tagare, D. K. Dubey, J. H. Jou and S. Vaidyanathan, Dyes Pigm., 2019, 160, 944–956.
20. S. Tannir, R. Chavez, G. Molina, A. Tomlinson and M. Jeffries-el, Chem. Mater., 2024, 36, 4945–4954.
21. Y. Ahn, S. Kim, J. Ho, W. Yeom, J. Lee and M. Chul, Dyes Pigm., 2022, 205, 110505.
22. S. Kang, H. Jung, H. Lee, S. Lee, M. Jung, J. Lee, Y. Chul and J. Park, Dyes Pigm., 2018, 156, 369–378.
23. M. Yu, S. Wang, S. Shao, J. Ding, L. Wang, X. Jing and F. Wang, J. Mater. Chem. C, 2015, 3, 861–869.
24. R. Kim, S. Lee, K. H. Kim, Y. J. Lee, S. K. Kwon, J. J. Kim and Y. H. Kim, Chem. Commun., 2013, 49, 4664–4666.
25. Z. Wu, X. Zhu, Y. Li, H. Chen, Z. Zhuang, P. Shen, J. Zeng, J. Chi, D. Ma, Z. Zhao and B. Z. Tang, Adv. Opt. Mater., 2021, 9, 2100298.
26. J. Xu, H. Liu, J. Li, Z. Zhao and B. Z. Tang, Adv. Opt. Mater., 2021, 9, 2001840.
27. A. R. Khosropour, M. M. Khodaei and H. Moghannian, Synlett, 2005, 955–958.
28. T. Viswanathan, N. Yadav, H. Nandish S, S. Pal, A. K. Mazumdar and P. Rajamalli, Chem. - Asian J., 2025, 20, e202401439.
29. B. Miehlich, A. Savin, H. Stoll and H. Preuss, Chem. Phys. Lett., 1989, 157, 200–206.
30. N. Yadav, U. Deori, E. Ravindran, B. Sk and P. Rajamalli, J. Mater. Chem. C, 2023, 11, 16368–16376.
31. N. Yadav, U. Deori, A. K. Manna and P. Rajamalli, Adv. Opt. Mater., 2025, 13, 2402820.
32. N. Yadav and P. Rajamalli, Org. Electron., 2025, 136, 107157.
33. S. Hüfner, Photoelectron Spectroscopy: Principles and Applications, Springer, Berlin, 3rd edn, 2003.
34. R. Guo, W. Liu, S. Ying, Y. Xu, Y. Wen, Y. Wang, D. Hu, X. Qiao, B. Yang, D. Ma and L. Wang, Sci. Bull., 2021, 66, 2090–2098.
35. Y. Wang, W. Liu, S. Ye, Q. Zhang, Y. Duan, R. Guo and L. Wang, J. Mater. Chem. C, 2020, 8, 9678–9687.
36. S. Kang, J. Huh, J. Kim and J. Park, J. Mater. Chem. C, 2020, 8, 11168–11176.
37. Q. Zhang, J. Li, K. Shizu, S. Huang, S. Hirata, H. Miyazaki and C. Adachi, J. Am. Chem. Soc., 2012, 134, 14706–14709.
38. M. Y. Wong, S. Krotkus, G. Copley, W. Li, C. Murawski, D. Hall, G. J. Hedley, M. Jaricot, D. B. Cordes, A. M. Z. Slawin, Y. Olivier, D. Beljonne, L. Muccioli, M. Moral, J. C. Sancho-Garcia, M. C. Gather, I. D. W. Samuel and E. Zysman-Colman, ACS Appl. Mater. Interfaces, 2018, 10, 33360–33372.
39. C. Li, Z. Ren, X. Sun, H. Li and S. Yan, Macromolecules, 2019, 52, 2296–2303.
40. D. H. Ahn, H. Lee, S. W. Kim, D. Karthik, J. Lee, H. Jeong, J. Y. Lee and J. H. Kwon, ACS Appl. Mater. Interfaces, 2019, 11, 14909–14916.
41. X. Zheng, X. Tian, Y. Li, H. Liu, S. Zhang and B. Yang, Org. Electron., 2024, 134, 107121.
42. Y. Xu, X. Liang, Y. Liang, X. Guo, M. Hanif, J. Zhou, X. Zhou, C. Wang, J. Yao, R. Zhao, D. Hu, X. Qiao, D. Ma and Y. Ma, ACS Appl. Mater. Interfaces, 2019, 11, 31139–31146.
43. H. Xu, L. H. Wang, X. H. Zhu, K. Yin, G. Y. Zhong, X. Y. Hou and W. Huang, J. Phys. Chem. B, 2006, 110, 3023–3029.
44. S. Y. Lee, T. Yasuda, Y. S. Yang, Q. Zhang and C. Adachi, Angew. Chem. Int. Ed., 2014, 53, 6402–6406.
45. S.-H. Hwang, Adv. Mater., 2015, 27, 2515–2520.
46. Y. J. Cho, S. K. Jeon and J. Y. Lee, Adv. Opt. Mater., 2016, 4, 688–693.
47. T. Miwa, S. Kubo, K. Shizu, T. Komino, C. Adachi and H. Kaji, Sci. Rep., 2017, 7, 284.
48. B. Li, Z. Li, T. Hu, Y. Zhang, Y. Wang, Y. Yi, F. Guo and L. Zhao, J. Mater. Chem. C, 2018, 6, 2351–2359.
49. P. Stachelek, J. S. Ward, P. L. Dos Santos, A. Danos, M. Colella, N. Haase, S. J. Raynes, A. S. Batsanov, M. R. Bryce and A. P. Monkman, ACS Appl. Mater. Interfaces, 2019, 11, 27125–27133.
50. S. G. Ihn, D. Jeong, E. S. Kwon, S. Kim, Y. S. Chung, M. Sim, J. Chwae, Y. Koishikawa, S. O. Jeon, J. S. Kim, J. Kim, S. Nam, I. Kim, S. Park, D. S. Kim, H. Choi and S. Kim, Adv. Sci., 2022, 9, 2102141.
51. N. Lin, J. Qiao, L. Duan, H. Li, L. Wang and Y. Qiu, J. Phys. Chem. C, 2012, 116, 19451–19457.
52. N. Lin, J. Qiao, L. Duan, L. Wang and Y. Qiu, J. Phys. Chem. C, 2014, 118, 7569–7578.
53. S. G. Ihn, N. Lee, S. O. Jeon, M. Sim, H. Kang, Y. Jung, D. H. Huh, Y. M. Son, S. Y. Lee, M. Numata, H. Miyazaki, R. Gómez-Bombarelli, J. Aguilera-Iparraguirre, T. Hirzel, A. Aspuru-Guzik, S. Kim and S. Lee, Adv. Sci., 2017, 4, 1600502.
54. D. H. Ahn, J. H. Maeng, H. Lee, H. Yoo, R. Lampande, J. Y. Lee and J. H. Kwon, Adv. Opt. Mater., 2020, 8, 2000102.
55. Y. H. Kim, S. Y. Lee, W. Song, S. S. Shin, D. H. Ryu, R. Wood, J. Yatulis and W. Y. Kim, J. Korean Chem. Soc., 2010, 54, 291–294.
56. H. Park, J. Lee, I. Kang, H. Y. Chu, J. I. Lee, S. K. Kwon and Y. H. Kim, J. Mater. Chem., 2012, 22, 2695–2700.
57. X. Zhao, L. Zhou, Y. Jiang, R. Cui, Y. Li and H. Zhang, Dyes Pigm., 2016, 130, 148–153.
58. N. Liu, Y. M. Zhou, D. Shelhammer and X. A. Cao, Opt. Mater., 2019, 95, 109232.
59. CCDC 2410935: Experimental Crystal Structure Determination, 2025 DOI:10.5517/ccdc.csd.cc2lxs3f.

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