The photochemistry of 6-phenanthridinecarbonitrile I. Product analysis

When 6-phenanthridinecarbonitrile (3) is irradiated at 2537 Angstrom in neu tral 9:1 2-propanol/water, three major products are formed. These are dimet hyl-(6-phenanthridinyl)methanol (4), phenanthridine (5) and 6,6'-biphenanth ridine (6). When benzophenone is present in the reaction mixture, diphenyl- (6-phenanthridinyl)methanol is also formed. 6-Phenanthridinyl radical which is common to the formation of all these products, is formed by a monophoto nic process involving hydrogen atom abstraction from an alcohol molecule by an excited state of 3. Unlike what is generally found with other nitrogen- heterocycles, the photochemistry of 3 appears to involve only a pi,pi* sing let state. The fluorescence of 3 is quenched with the triplet quencher cis/ trans-piperylene as a function of the concentration of the diene without th e accompaniment of an exciplex emission.