Temperature Effect on the Absorption and Fluorescence Spectra of p-Cyano-N,N-dimethylaniline in Dichloroethane and Ethyl Acetate

Abstract

Abstract The effect of temperature (293 ÷ 413 K) upon absorption and fluorescence spectra of p-cyano-N,N-dimethylaniline (CDMA) was investigated in 1,2-dichloroethane and ethyl acetate. Two fluorescence bands, a and b, were already observed at 293 K, with the intensity of band b increasing strongly with temperature in both solvents. The absorption and fluorescence b bands of CDMA were found to be independent of the orientation interaction with the solvent. On the other hand, the longwave band of fluorescence a undergoes a strong hypsochromic shift resulting from the decrease in the permittivity with increasing temperature. Based on these observations, the electric dipole moment μe in the 1Lb state (shortwave band of fluorescence b) was found to be equal to the dipole moment,μg, in the ground state. The electric dipole moment μe in the 1La state (the longwave band of fluorescence a), which is strongly stabilized by the polar solvent, is about 2.5 times as high as μg , amounting to 54 x 10- 0 Cm (16.2 D) for μg = 22.5 x 10 -30 Cm (= 6.75 D).