Photodissociation of molecules of benzene and some of its derivatives in the liquid phase

The effect of intramolecular interactions on photodissociation has been studied. The quantum yields have been determined for the primary free radicals of benzene, its polymethyl-substituted derivatives Ph-(CH₃), and its monosubstituted Ph-(CH₂)-X derivatives, where X is a substituent containing a heteroatom. The conclusion made previously on the importance of singlet-singlet deactivation in nonradiative transitions of an excited molecule has been confirmed. The compounds Ph-(CH₂)-X have different photolytic stability on excitation by different normal vibrations within the limits of a single electron absorption band, A comparison of the spectral data with the photodissociation data for Ph-(CH₂)n-X enable us to propose that, depending on the nature of the intramolecular interactions, a transfer of both electron and vibrational excitation energy may take place from the ring to the substituent. This process is exceeded in the latter case by the conversion of electron excitation to vibrational excitation.We thank Professor Kh. S. Bagdasar'yan for his interest in the investigation and for discussion of the results.