Effect of partial and complete deuteration on the phosphorescence lifetime of phenylacetylene

Phosphorescence lifetimes measured for C6K5CCH, C6H5CCD, C6D5CCH, and C6D5CCD in rigid glasses at 77 degrees K show that deuterium substitution for the single acetylenic hydrogen has almost the same effect as deuterium substitution for all five phenyl ring hydrogens in altering the radiationless deactivation of the triplet state. The involvement of an out-of-plane bending of the hydrogens of the ring and a non-totally symmetric (probably also out-of-plane) vibration of the acetylenic hydrogen in the non-radiative transition is suggested.