Fluorescent solvatochromism and nonfluorescence processes of charge-transfer-type molecules with a 4-nitrophenyl...

A novel naphthalene derivative, 1-methoxy-4-(4-nitrophenyl)naphthalene (1), exhibited obvious fluorescence, the color of which varied significantly from greenish blue to red depending on the solvent, from the charge-transfer excited state with a large electric dipole moment. The fluorescence of 1 was weak in both low- and high-polar solvents, and the fluorescence of derivatives with a 4-nitrophenyl group was also weak in low-polar solvents. Such unusual solvent dependences were revealed by the energy gap plot. The high-energy fluorescent excited state of a derivative with the 4-nitrophenyl group is quickly converted into the triplet excited state, whereas the low-energy state deactivates to the ground state through internal conversion. Such nonfluorescence processes of the derivatives were elucidated by developing derivatives with a nitro group that exhibited fluorescence changes in the broad visible region depending on the chemical structure and solvent.