Pd‐Catalysed Direct Arylation of Distyrylbenzene: Strong Dual‐state Fluorescence and Electrochromism

Distyrylbenzenes (DSBs) are well‐known for their strong multicolour fluorescence. Fluorescence tuning of DSB via further functionalization/arylation, on the other hand, is uncommon. This paper reports a Pd‐catalysed direct arylation approach for introducing different aryl groups onto fluorobenzene‐containing DSB moiety (7) in high yields (67‐72%). The versatile methodology allows the substitution of neutral, electron‐deficient and electron‐rich aryl groups. The electron‐deficient aryls render mono‐substitution, while the electron‐rich counterparts promote di‐substitution. The compounds (1‐6) show blue, green, and yellow fluorescence in both the solution and solid states; the fluorescence quantum yields reach 100% and the peak maxima span from 425 to 560 nm. The mono‐carbazole DSB(5) exhibit white light emission(WLM) in polar solvents (acetone, DMF, CH3CN, DMSO and NMP) with very high fluorescence quantum yields(ϕf) of 60‐80%. For WLM, such high efficiency (ϕf) is somewhat uncommon. Moreover, visible‐to‐NIR reversible electrochromism is demonstrated by the TPA‐integrated DSB(6). The colour of 6 changes from pristine light yellow to orange, and the absorption maxima shifts from 372 to 1500 nm when a positive potential of 1.0 V vs Ag/Ag+ is applied. Moreover, the system shows high colouration efficiency in the NIR region with fast switching speeds for colouration and decolouration as fast as 0.98s and 1.05s.