Synthesis of novel bisaryl naphthalimide compounds and investigation of their photochromic fluorescence properties

The objective of the research was to synthesise new photo switchable photochromic fluorescence compounds. Starting from 4-bromo-N-butyl-3-iodo-1,8-naphthalimide four new compound: 3,4-Bis(2-phenyl-5-methyl-4-thiazolyl)-N-butyl-1,8-naphthalimide 2.10, 3,4-Bis(3,5-dimethyl-4-isoxazolyl )-N-butyl-1,8-naphthalimide 2.12, 3,4-Bis(3,5-dimethyl-4-pyrazolyl)- N-butyl-1,8-naphthalimide 2.14 and 3,4-Bis(1,3,5-trimethyl-4-pyrazolyl)-N-butyl-1,8-naphthalimide 2.16 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 only photochrome 2.10 displayed photochromism. On exposure to ultraviolet light, the photochrome 2.10 showed a pale yellow to blue-green colour change due to the formation of ring closed form 2.10 C, which reversed to the ring opened form 2.10 on exposure to visible light. Conversion ratio and quantum efficiency (from O to C form) for 2.10 were also determined. Additionally, a solvent effect on the fluorescence properties of 2.10 was investigated. Increase of solvent polarity results in a red shift (to longer wavelengths) of the fluorescence emissions. Keywords: Photochromism, Fluorescence, Naphthalimide, Solvent effect