Donor Influence on the Optoelectronic Properties of N‐Substituted Tetraphenylimidazole Derivatives

Abstract

Three new 1,2,4,5-tetraphenylimidazole derivatives, 9,9-dimethyl-10-(4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenyl)-9,10-dihydroacridine (DMAC-TPI), 10-(4-(2,4,5-triphenyl-1H-imidazol-1yl)phenyl)-10H-phenoxazine (PXZ-TPI), and 10-(4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenyl)-10H-phenothiazine (PTZ-TPI), bearing different electron donors at the N1 position of the imidazole were synthesised and characterised. DMAC-TPI and PXZ-TPI showed narrow emission at λ PL of 388 and 418 nm in toluene, and in doped films in Zeonex polymer (1 wt.%) at λ PL 381 and 407 nm, respectively, with a full width at half maximum (FWHM) ranging 0.42-0.44 eV. DMAC-TPI and PXZ-TPI are predicted to show very low oscillator strength for the low-energy transitions, which aligns to the observed low photoluminescence quantum yields. Both molecules showed a singlet-triplet energy gap (ΔE ST of around 1.2 eV) that is much too large to enable reverse intersystem crossing and thermally activated delayed fluorescence. Connecting a donor group to TPI at the N1 position can lead to room temperature phosphorescence (RTP), as the example of PTZ-TPI showed.

Exploring the Versatile Uses of Triplet States: Working Principles, Limitations, and Recent Progress in Phosphorescence, TADF, and TTA

“…Regarding molecular design, various D and A groups have been employed over the years to synthesize these D–A and/or D-A-D types of TADF molecules and evaluate their potential. − In reviews by Dias et al . and Huang et al ., nitrogen-based donor units, e.g., carbazole, diphenyl amine, phenoxazine, acridine, and their derivatives, are shown to be the most commonly employed donor units.…”