FLUORESCENCE ENHANCEMENT FROM SELF-ASSEMBLED AGGREGATES II: FACTORS INFLUENCING FLORESCENCE COLOR FROM AZOBENZENE AGGREGATES

We have chosen two types of azobenzene derivatives to elucidate the correlation between molecular structure and fluorescence color of light-driven azobenzene-based aggregates. The fluorescence color from azobenzene molecules (1 and 2), adopting a planar structure, was obviously red-shifted from that of the corresponding twisted ortho-alkylated azobenzene 3. The steric hindrance resulting from bulky alkyl groups at the ortho position of the azo linkage was considered to lessen the intermolecular pi - pi stacking between aromatic rings, leading to the relatively smaller spectral shift in fluorescence from the absorption band of the initial azobenzene solution. The substitution of electron-withdrawing groups into the azobenzene core gave rise to a blue-shift in fluorescence wavelength. That is, the extended pi-conjugated system consisting of a planar azobenzene core as well as the electronic properties of the substituents are key factors influencing the fluorescence color from the light-driven azobenzene aggregates. Moreover, we could prepare fluorescent polymer films by mixing fluorescent azobenzene aggregates with polymers. The fluorescence colors from the polymer films were comparable to those from the azobenzene aggregates.