Dendron-containing tetraphenylethylene compounds: dependence of fluorescence and photocyclization reactivity on the dendron generation

Abstract

The synthesis and characterization of four dendron-containing tetraphenylethylenes (TPEs), 1(1)-1(4), were synthesized, along with a TPE compound that contained four OCH(2) Ph groups (referred to as 1(0)) for comparison. Photophysical studies revealed that the TPE core became emissive after linking dendrons onto its periphery. Moreover, the fluorescence intensity was significantly enhanced when high-generation dendrons were linked onto the TPE core; the fluorescence intensity increased in the following order: 1(1)<1(2)<1(3)<1(4). This phenomenon was tentatively attributed to an enhancement in the energy barrier for internal rotation and torsion of the TPE core to which four dendrons were connected. In addition, the photocyclization of the TPE core into the respective 9,10-diphenylphenanthrene was facilitated when high-generation dendrons were linked to the TPE core. Again, the photocycliztion reactivity increased in the following order: 1(1)<1(2)<1(3)<1(4). We found that the fluorescence and photocyclization reactivity of TPE could be modulated by covalent interactions with dendrons, and such modulation was strongly dependent on the dendron-generation.