Synthesis of a naphthalenediimide with photo-induced fluorescence enhancement and its visual dual-response to highly polar solvents

A photochromic 1,4,5,8-naphthalenediimide (NDI) derivative N,N-bis(4,6- diamino-1,3,5-triazinyl-2-)naphthalenediimide (DDNDI) was synthesized and the photo-induced fluorescence enhancement of DDNDI was found for the first time for NDI materials, the fluorescence intensity increases with the increase of sunlight or UV irradiation time. For sunlight irradiation, it shows a linear relationship of y=22.38821x+85.37868 (R=0.9987). And the photochromism and fluorescence of the DDNDI solution have synchronous “on-off” characteristic. Under continuous irradiation, the photochromic color of the DDNDI solution changes from colorless to yellow and the fluorescence color changes from colorless to green. After adding polar solvent, photochromism and fluorescence can be suppressed simultaneously due to the twisted intramolecular charge transfer (TICT) and the photoinduced electron transfer (PET). Based on the dual changes of photochromic and fluorescent colors caused by UV, visual dual-response to highly polar solvents can be observed, and the fluorescence intensity is linearly related to the amount of the added DMSO: y=-1.21857x+780.04855 (R=0.9966). • Photo-induced fluorescence enhancement for the naphthalenediimide materials is found first. • The photo-induced fluorescence enhancement is linearly related to the sunlight irradiation time. • The mechanism is investigated by the turn on and off of the fluorescence and photochromism simultaneously.