Synthesis and Photochromic Properties of Diaryl [5]Helicene Derivatives

Abstract

Photoinduced tuning of aromaticity and correlative molecular properties has attracted enormous interest in recent years for both modulating photochromism properties and designing novel photochromic materials. Here, we report on the synthesis and photochemical characterizations investigation of diaryl[5]helicene based diarylethene molecular switches. 3,4‐Bis(2,4‐dimethyl‐5‐phenylthiophen‐3‐yl)dibenzo[c,g]phenanthrene derivative 1a showed no photochromic reaction, while 3,4‐bis(2‐methyl‐5‐phenylthiophen‐3‐yl)dibenzo[c,g]phenanthrene derivative 2a and 3,4‐bis(5‐methyl‐2‐phenylthiazol‐4‐yl)dibenzo[c,g]phenanthrene derivative 3a exhibited reversible photochromism in different aprotic solvents with specific light irradiation. Meanwhile, the diarylethene compounds 2a and 3a underwent turn‐off mode fluorescence photoswitchings together with the photoisomerization reaction upon light irradiation. Remarkably, the photoinduced changes in aromaticity of [5]helicene as a central ethene bridge along with the relative smaller activation energy and higher frequency factor facilitated the thermal bleaching rates of diarylethene switches 2 and 3 in solution. This research provides a new insight for designing aromatic diarylethene photoswitches for reversible fluorescence switching behaviour, photoinduced changes in aromaticity and further fast thermal back reaction.