Dihydroazulene‐Boron Subphthalocyanine Conjugates with Oligo(phenyleneethynylene) Bridging Unit: Photoswitchable Fluorophores

In this work, we have linked the dihydroazulene (DHA)/vinylheptafulvene (VHF) photo‐/thermoswitch and the boron subphthalocyanine (BsubPc) fluorophore via an axial oligo(phenyleneethynylene) bridging unit into new DHA‐BsubPc conjugates. The objectives were to elucidate the influence of BsubPc on the DHA/VHF switching reactions and the influence of DHA/VHF on the BsubPc fluorescence in these conjugates for which the entire axial substituent connected to boron comprises one large, conjugated scaffold. We present the synthesis and properties of DHA‐BsubPc conjugates with varying peripheral substituents on the BsubPc core, being either unsubstituted (H12BsubPc) or partially fluorinated (F6BsubPc). Fluorination of the BsubPc core provided a remarkable increase in the reversibility of the DHA‐VHF interconversions promoted by light and heat, respectively, and accompanied by on/off switching of the BsubPc fluorescence. Synthetically, the units were connected using Sonogashira coupling reactions of suitable acetylenic building blocks. Dihydroazulene – Boron subphthalocyanine (DHA‐BsubPc) conjugates were prepared, and the influence of the BsubPc, without or with peripheral fluorine substituents, on the ability of the DHA to photoisomerize into a vinylheptafulvene (VHF) was studied and vice‐versa the influence of the DHA and VHF on the BsubPc fluorescence (on/off).