Phosphorescence studies of 3.PI..PI.* benzaldehyde, acetophenone, and 1-indanone in benzoic acid host.

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We have made a vibrational analysis of the phosphorescence spectra of benzaldehyde, deuterated benzaldehydes, acetophenone, and 1-Indanone in benzoic acid host. The emissions coming from different sites of benzaldehyde were separated with the help of microwave induced delayed phosphorescence (MIDP) spectroscopy. From the phosphorescence excitation spectra the locations of the 3nπ* states were estimated to be about 2000 cm－1 above the 3ππ* states. Contrary to the previous assignment, it was found that the aldehyde H wag is active in the spectra of benzaldehyde as in the cases of other host. The spectra of acetophenone and 1-indanone are similar to those obtained in other hosts, although the 0-0 bands are relatively stronger. The C=O stretching mode is, however, not clearly observable in all the systems studied here, suggesting that this mode is not active in the spectra of nearly pure 3ππ* aromatic carbonyls. The main radiative mechanisms are discussed based on the present results and are compared with those of other aromatic carbonyls. Possible effects of hydrogen bonding on these properties are discussed.