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

The effect of temperature (293 -H41 3 K) upon absorption and fluorescence spectra of p-cyanoN,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 /xe in the *£.,, state (shortwave band of fluorescence b) was found to be equal to the dipole moment, in the ground state. The electric dipole moment n t in the 'La state (the longwave band of fluorescence a), which is strongly stabilized by the polar solvent, is about 2.5 times as high as ng, amounting to 54 x 10~° Cm (16.2 D) for ng = 22.5 x lO 3 0 Cm ( = 6.75 D).