Time-resolved spectroscopic study of the initial process of photopolymerization in a diacetylene crystal

The optical absorption change and luminescence induced by electron-pulse irradiation have been studied for crystalline 5,7-dodecadiyne-1,12-diol bis[phenylcarbamate] (TCDU). The triplet state of TCDU is identified for the first time; it shows an optical absorption band at 3.96 eV and a luminescence band at 2.57 eV. At higher temperature, the reactive dimer which shows an absorption band at 2.53 eV is generated. Examination of the correlation between the decay of the lowest triplet state and the dimer formation strongly suggests that the dimer is formed not via the lowest triplet state, but through relaxation at higher excited states.