Photo-induced fluorescence emission enhancement of azobenzene thin films

UV irradiation-induced fluorescence enhancement of thin films composed of azobenzene amphiphiles, C12AzoC10N+ (AzoN+), was investigated. UV irradiation to Langmuir–Blodgett (LB) monolayers of AzoN+ indicated that the fluorescence emission from an irradiated area was enhanced and the emission was independent of the aggregation structures of an azobenzene moiety. Moreover, UV irradiation to cast films of AzoN+ revealed that the enhancement was increased by increasing the irradiation time. The fluorescence by excitation at 365 nm occurred over a wide range of wavelengths from around 400 nm to 650 nm, and the emission was not attributed to the J-aggregates of AzoN+. The mechanism for this phenomenon has not been elucidated. It may be caused by the photo-chemical reaction of the azobenzene moiety or photo-induced specific aggregates. However, UV irradiation-induced fluorescence enhancement can be applicable to optical memory devices.