Photophysical and Photochemical Properties of Polyurethane Coumarin Studied by Means of Electronic Spectra

Abstract

The spectroscopic and photochemical properties of polyurethane coumarine (PUC) in dimethyl sulf-oxide (DMSO), thetra hydro furan (THF), dimethyl formamide (DMF) and film state were investigated at room temperature under one photon excitation. Photodimer products were formed via UV irradiation. Syn head-to-head and syn head-to-tail photodimers were formed under one-photon (broadband UV) irradiation in polar solvents. The spectral investigation of the photochemical products of PUC revealed efficient fluorescence emission in the spectral region 300�400 nm, attributed to the syn-head-to-tail dimers of PUC. The results show that under irradiation of l ] 310 nm photodimerization process are increased and under UV irradiation with l [ 260 nm, photocleavage degree have been evidenced, too. Fluorescence spectra analysis of PUC in polar and film-based solvents reveals another very important result. The 375nm fluorescence wavelength of the PUC (exciting beam 310 nm) is about 30 times more intense than the same maximum in THF and in DMF. This result indicates a new method to confirm that PUC film photodimerisation occurs especially at its surface.