PHOTOPHYSICS AND PHOTOCHEMISTRY OF NITROANTHRACENES .1. PRIMARY PROCESSES IN THE PHOTOCHEMICAL-REACTIONS OF 9-BENZOYL-10-NITROANTHRACENE AND 9-CYANO-10-NITROANTHRACENE STUDIED BY STEADY-STATE PHOTOLYSIS AND NANOSECOND LASER PHOTOLYSIS

The genuine phosphorescence spectra of the title compounds (XNA) have been clearly observed at 77 K in EPA (diethyl ether-isopentane-ethanol 5:5:2 volume ratio). Also, the time-resolved absorption spectra obtained at the end of nanosecond laser pulse at 77 K (in EPA) and at room temperature (in ethanol and benzene) have been ascribed to the superposition of the absorptions of the lowest triplet XNA [3XNA(T1)] on those of the corresponding anthryloxy radicals (XAO.). The decay of 3XNA(T1) is not accompanied by the formation of XAO. and the following results are obtained. (1) In ethanol at room temperature, the first-order decay of XAO. corresponds to hydrogen-atom abstraction by XAO. from the solvent, giving rise to the formation of corresponding anthrols (XAOH), while the second-order reaction of XAO. with nitrogen(II) oxide (NO.) yields the corresponding nitrosoanthrones (XNSAN) which decompose very slowly into XAO. and NO. followed by the rapid formation of XAOH. (2) In benzene at room temperature no formation of XAOH is observed, but there exists an equilibrium between XAO.(+ NO.) and XNSAN. All these results support our previous conclusion that the nitro --> nitrite rearrangement of XNA does not occur for the lowest triplet states of pi-pi* character but does occur for the higher triplet states of n-pi* character, followed by the cleavage of the nitrites to XAO. and NO..