Observation of the S-2-emission from 1,4-anthraquinone

Emission, excitation, and absorption spectra of 1,4-anthraquinone (1,4-AQ) have been measured in a degassed CCl4 fluid solution at different temperatu res. It is shown that 1,4-AQ in CCl4 exhibits weak emission which can be at tributed to the S-2(pi, pi*) fluorescence at comparatively high temperature . The S-2(pi, pi*) state is considered to be in thermodynamic equilibrium w ith the S-1(n, pi*) state as well as with the T-2(n, pi*) and T-1(n, pi*) s tates. The present observation provides the first example of the S-2 emissi on from the medium-size molecules containing C=O groups.