posted on 2021-09-30, 09:13authored byHiromasa Nishikiori, Yosuke Kageshima, Nasrin Hooshmand, Mostafa A. El-Sayed, Katsuya Teshima
A temporal
change in acidity on the titania surface during UV irradiation
was indirectly monitored by evaluating the deposited fluorescein dye
using surface plasmon resonance spectroscopy such that gold nanoparticles
were embedded under the titania thin film in order to increase the
sensitivity. The fluorescence signal mainly originated from the highly
fluorescent dianion species of fluorescein in the fluorescence time
profiles after the femtosecond laser excitation. The signal monotonously
decayed with a single exponential function on silica, whereas the
signal rose and decayed with a double exponential function on the
titania. The present femtosecond time-resolved fluorescence study
revealed that a process involving the transformation from the monoanion
to dianion of fluorescein “in the excited states”, i.e.,
the excited state proton transfer from the dye molecule to the titania
surface, induced the subsequent fluorescence process, which had not
been detected by the previous transient absorption or nanosecond fluorescence
measurements.