Benzoxazole-Based Hybridized Local and Charge-Transfer Deep-Blue Emitters for Solution-Processable Organic Light-Emitting Diodes and the In fluences of Hexahydrophthalimido

Abstract

Hybridized local and charge-transfer (HLCT) emitters have attracted extensive attention, but the insolubility and severe self-aggregation tendency restrict their applications in solution-processable organic light-emitting diodes (OLEDs), particularly deep-blue OLEDs. Herein, two novel benzoxazole-based solution-processable HLCT emitters (BPCP and BPCPCHY) are designed and synthesized, in which benzoxazole acts as an acceptor, carbazole acts as a donor, and hexahydrophthalimido (HP, with a large intramolecular torsion angle and spatial distortion characteristics) acts as a bulky modified end-group with weak electron-withdrawing effects. Both BPCP and BPCPCHY exhibit HLCT characteristics and emit near ultraviolet in toluene at 404 and 399 nm. Compared to the BPCP, the BPCPCHY solid shows much better thermal stability (T g, 187 vs 110 °C), higher oscillator strengths of the S1-to-S0 transition (0.5346 vs 0.4809), and faster k r (1.1 × 108 vs 7.5 × 107 s–1) and thus a much higher ΦPL in the neat film. The introduction of HP groups greatly suppresses the intra-/intermolecular charge-transfer effect and self-aggregation trends, and the BPCPCHY neat films placed in air for 3 months can still maintain an excellent amorphous morphology. The solution-processable deep-blue OLEDs utilizing BPCP and BPCPCHY achieved a CIEy of 0.06 with maximum external quantum efficiency (EQEmax) values of 7.19 and 8.53%, respectively, which are among the best results of the solution-processable deep-blue OLEDs based on the “hot exciton” mechanism. All of the above results indicate that benzoxazole is an excellent acceptor for constructing deep-blue HLCT materials, and the strategy of introducing HP as a modified end-group into an HLCT emitter provides a new perspective to develop solution-processable efficient deep-blue OLEDs with high morphological stability.

Rational Design of Coumarin‐Based Hybridized Local and Charge‐Transfer Blue Emitters for Solution‐Processed Organic Light‐Emitting Diodes

“…The correlations between Stokes shifts $${\left({v}_{{\rm a}}-{v}_{{\rm f}}\right)}$$ in different solvents and orientation polarizations $${f(\varepsilon{}, n)}$$ of the corresponding solvents are plotted as shown in Figure 5d–f. On the basis of Lippert‐Mataga model, the dipole moments ( μ e ) for excited states are obtained from the slope of the fitted lines [8e,16c] . pPh‐7P, pPh‐7M, and pPh‐6M have two distinct slopes in low‐ and high‐polarity solvents, indicating the presence of two diverse excited state behaviors.…”

A record-high EQE of 7.65%@3300 cd m−2 achieved in non-doped near-ultraviolet OLEDs based on novel D′–D–A type bipolar fluorophores upon molecular configuration engineering

“…Notably, such high PLQY values achieved in neat lms are higher than those of most reported HLCT emitters. 58,[68][69][70][71][72] By comparison with other isomers, 3,6-mPPICNC3 exhibits a blue-shi with higher color purity, which can be attributed to the rigid conguration and large steric hindrance effect that can effectively suppress the structure relaxation and intermolecular aggregation. The doped lm with a 5 wt% emitter dispersed into polar poly(methyl methacrylate) (PMMA) exhibits blue-shied PL peaks of 399, 425, 422 and 443 nm, with the enhanced PLQYs of 61.4%, 93.4%, 91.0% and 97.4% (Fig.…”

Oxygen heterocyclic coumarin-based hybridized local and charge-transfer deep-blue emitters for solution-processed organic light-emitting diodes

“…S21 (ESI †), the UV-vis absorption spectra in different polarity solvents exhibit minor changes in the dipole moment for the ground state, attributed to their comparable absorption wavelengths. [54][55][56] The maximum emission wavelengths of BCz-6P, pPh-6P, and oPh-6P exhibit significant redshifts of 90, 79, and 83 nm from low-polarity dimethoxymethane to highpolarity acetonitrile, indicating the intramolecular CT characteristics of the excited state. The correlations between the Stokes shift (v a À v f ) in different solvents and the orientation polarizations f (e,n) of the corresponding solvents are plotted as shown in Fig.…”

“…According to the Lippert-Mataga model, the excited state dipole moments (m e ) of materials are derived from the slope of the fitted line. 16,56 A non-linear correlation with two distinct slopes in the plots for low-and high-polarity solvents indicates the presence of two diverse excited state behaviors. The LE state dominates in the low-polarity solvents ( f o 0.20), while the CT state dominates in the high-polarity solvents ( f 4 0.20).…”