Realization of efficient deep-blue anthracene-based emitters with superior film-forming and charge transport properties is challenging. A series of non-symmetric 9,10-diphenylanthracenes (DPA) with phenyl and pentyl moieties at the 2nd position and alkyl groups at para positions of the 9,10-phenyls were synthesized and investigated. The non-symmetric substitution at the 2nd position enabled to improve film forming properties as compared to those of the unsubstituted DPA and resulted in glass transition temperatures of up to 92 °C. Small-sized and poorly conjugated substituents allowed to preserve emission in the deep blue range (<450 nm). Substitution at the 2nd position enabled to achieve high fluorescence quantum yields (up to 0.7 in solution, and up to 0.9 in the polymer host), although it caused an up to 10-fold increase in the intersystem crossing rate as compared to that of the unsubstituted DPA. Further optimization of the film forming properties achieved by varying the length of the alkyl groups attached at the 9,10-phenyls enabled to attain very high hole drift mobilities (∼5 × 10(-3)-1 × 10(-2) cm(2) V(-1) s(-1)) in the solution-processed amorphous films of the DPA compounds.

Triplet–triplet annihilation (TTA) is an attractive way to boost the efficiency of conventional fluorescent organic light-emitting diodes (OLEDs). TTA-active anthracene derivatives are often considered as state-of-the-art emitters due to the proper energy level alignment. In this work, TTA properties of a series of highly fluorescent nonsymmetrical anthracene compounds bearing 9-(4-arylphenyl) moiety and 10-(4-hexylphenyl) fragments were assessed. Two different methods to enhance the TTA efficiency are demonstrated. First, the intensity of TTA-based delayed fluorescence directly depended on the intersystem crossing (ISC) rate. This ISC rate can be significantly enhanced in more conjugated compounds due to the resonant alignment of S1 and T2 energy levels. While enhanced ISC rate slightly quenches the intensity of prompt fluorescence, the rise of the triplet population boosts the intensity of resultant delayed fluorescence. Second, the triplet annihilation rate can be significantly enhanced by optimization of triplet exciton diffusion regime in the films of anthracene derivatives. We show that the proper layer preparation technology has a crucial influence on uniformity and energetic disorder of the film. This enhances the nondispersive triplet diffusion and increases the resulting delayed fluorescence intensity.

Singlet−Triplet energy exchange is an area of active research due to its role in optoelectronic devices and photodynamic therapy. Large spin−orbit coupling (SOC) is difficult to achieve in simple hydrocarbon structures limiting the intersystem crossing (ISC) rates. A new approach to enhance the spin−orbit coupling via helical molecular orbitals is investigated in oligoyne-bridged bifluorenes. Transient absorption studies showed a singlet-to-triplet ISC rate of up to 6 ns −1 resulting in 0.84 triplet yield. Density functional calculations revealed a direct relation between high ISC and large SOC values mediated by helical molecular orbitals. Calculations and spectroscopic data also suggested that El-Sayed forbidden ISC occurs as a direct transition between 1 ππ* and 3 ππ*, which becomes allowed due to a symmetry-breaking interaction leading to mixing between orthogonal π-systems in the oligoyne fragment.

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