Abstract
Chiral aryl 4-tolyl sulfoxides substituted with several sizes of aromatic rings, (S)-(-)-phenyl 4-tolyl sulfoxide (PHSO), (R)-(+)-1-naphthyl 4-tolyl sulfoxide (NASO), (R)-(+)-9-phenanthryl 4-tolyl sulfoxide (PNSO), and (R)-(+)-1-pyrenyl 4-tolyl sulfoxide (PYSO), were prepared. It has turned out for the first time that there are n-sigma*, pi-sigma* and pi-pi* states in excited states of these molecules by MO calculation. Fluorescence spectra and quantum yields of fluorescence, Phi_fl, were measured in polar and non-polar solvents. Quantum yields of photoinversion, Phi_inv, and photolysis, Phi_dec, were also obtained with CD and HPLC measurements. Aromatic-ketone like characteristics have been noticed in the fluorescence measurements, i.e., fluorescence has been observed from sulfoxides substituted with large aromatic rings and their fluorescence becomes strong in a polar solvent. We attributed these characteristics to the decrease in pi-pi* transition energy as the degree of conjugation increases, while n-pi* and pi-sigma* transition energy does not decrease so much. The values of Phi_inv and Phi_dec for PHSO, NASO and PNSO were found to be 0.3-0.4 (Phi_inv) and 0.03-0.05 (Phi_dec). The quantum yields for PYSO were measured as Phi_inv=0.02-0.03 in methanol and hexane, and Phi_dec=0.002-0.003 in methanol and 0.012-0.016 in hexane. It was found that quantum yields of photoinversion and photolysis decrease as the pi-pi* transition energy decreases. We concluded that photoinversion occur during change in electronic states from n-pi* states to the ground state.