synthesis of novel diarylethenes bearing naphthalimide moiety and photochromic fluorescence behaviors

The objective of the research was to synthesise new photo switchable photochromic fluorescence compounds. Starting from N-butyl-4-bromo-3-iodo-1,8-naphthalimide new compounds: 3,4-Bis(2-phenyl-5-methyl-4-thiazolyl)-N-butyl-1,8-naphthalimide 1O and 3,4-Bis(3,5-dimethyl-4-isoxazolyl)-N-butyl-1,8-naphthalimide 2O were prepared via two step Suzuki coupling reaction of aryl boronic acid and esters, and their photochromic fluorescence properties were investigated. Although all prepared bisaryl naphthlimides were fluorescence due to the naphthlimide moiety, among them photochrome 1O displayed photochromism. On exposure to ultraviolet light, the photochrome 1O showed a pale yellow to blue-green colour change due to the formation of ring closed form 1C, which reversed to the ring opened form 1O on exposure to visible light. Conversion ratio and quantum efficiency (from O to C form) for 1O were also determined. Additionally, a solvent effect on the fluorescence properties of 1O and 2O was investigated. Increase of solvent polarity results in a red shift (to longer wavelengths) of the fluorescence emissions.