Preparation of ethynyl‐substituted picenes and their electronic absorption and fluorescence spectra: Effects of the ethynyl substitution positions on the spectral behavior

A series of [5]phenacene (picene) incorporating (triisopropylsilyl)ethynyl functionality, TSEP s, was conveniently synthesized via a Mallory photoreaction–Sonogashira reaction sequence. For the Sonogashira reaction of 1‐bromopicene, an unexpected 14‐(triisopropylsilyl)ethynyl‐substituted product, 14‐TSEP , was afforded along with the normal Sonogashira‐reaction product, 1‐TSEP . The UV–Vis and fluorescence spectra of TSEP s were observed to reveal the effects of the position and number of ethynyl functionalities on the electronic features of TSEP s. All TSEP s investigated displayed a small absorption band ( 1 L b ) in the 382–398 nm wavelength region, and a larger one ( 1 L a ) in the 325–371 nm wavelength region. The shift of the absorption bands was more pronounced for the 1 L a band compared with the 1 L b band. Within the TSEP series, a fluorescence quantum yield of 5,8‐TSEP ( Φ F = 0.25) was the largest and that of 2‐TSEP was the smallest (0.08). The spectral features of the picene chromophore were found to be manipulated by the position and number of TIPS substituents.