Novel fluorescence-enhancing effect based on light-induced E/Z isomerization of perylene diimides with Schiff-base groups on bay-positions

Three novel perylene Schiff-base derivatives 5a-5c were synthesized and characterized in yields of 80-85%. They exhibited reversible trans/cis isomerization after UV-light irradiation and heating. The fluorescence-enhancing effects were firstly observed for perylene trans-to-cis isomerization. The increasing steric hindrance based on the restricted intramolecular rotation of trans-to-cis isomerization was responsible for the fluorescence-enhancing effect. The larger substituent on Schiff-based groups leaded to stronger fluorescence intensity and high quantum yield.