Functionalization at C1 of the Dihydroazulene/Vinylheptafulvene Photo‐/Thermoswitch – Establishing Structure‐Property Relationship

The optical and switching properties of the dihydroazulene/vinylheptafulvene (DHA/VHF) photo‐/thermoswitch can be finely tuned by substituent groups at specific positions. While the kinetics of the thermal ring closure of VHF into DHA have previously been shown to follow systematic trends in regard to the electron‐withdrawing/donating character of substituents at DHA positions C2, C3, and C7 (Hammett correlations), no such correlation has so far been established for a selection of compounds with different substituents at C1. Functionalization at this position is at the same time known to have the strongest impact on the VHF‐to‐DHA conversion rate. Here we show that introduction of a benzothiazole ring at C1 of DHA (corresponding to the vinyl position of VHF) with various electron‐withdrawing/donating groups provides VHFs whose rates of ring closure follow a Hammett correlation – the more electron‐withdrawing substituent on the benzothiazole, the faster ring closure reaction.