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 [tolyl (1)], electron-deficient [p-formyl benzene (2), p-acetyl benzene (3), p-nitrobenzene (4)] and electron-rich [carbazole (5), triphenylamine (6)] 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 >98 % 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 0.98 s and 1.05 s.