PHOTODISSOCIATION OF HALOAROMATICS - DETECTION, KINETICS, AND MECHANISM OF ARYLMETHYL RADICAL FORMATION
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The photodissociation of 1- and 2-(halomethyl)naphthalenes in room-temperature hexane solution was studied by means of picosecond emission and absorption spectroscopy. Excitation of the (halomethyl)naphthalenes at 266 or 299 nm into the S2(,*) state caused the molecules to undergo carbon-halogen bond homolysis. Emission from the 1- and 2-naphthylmethyl radicals was observed when a 355-nm, 25-ps pulse was directed into the sample at times ranging from 0 ps to 40 ns after the arrival of the first photolysis pulse. A broad absorption in the spectral region between 325 and 395 nm was observed for the 1-naphthylmethyl radical with a maximum near 365 nm and for the 2-naphthylmethyl radical with a maximum near 380 nm which appeared within the laser pulse width and persisted for times longer than 500 ps after excitation. A mechanism incorporating the experimental data is proposed for the photodissociation of (halomethyl)naphthalenes which is quite generally applicable to haloaromatic compounds. Excitation of the S2(,*) state results in energy dissipation through two channels: (1) internal conversion to S1(,*) followed by fluorescence to S0 and (2) intersystem crossing to an upper triplet state which is itself, or crosses to, a dissociative (,*) triplet state that leads to homolysis of the carbon-halogen bond. The branching ratio of channel 2 to channel 1 was found to be 6:1 for 2-(chloromethyl)naphthalene in hexane at room temperature. 1984, American Chemical Society. All rights reserved.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
author list (cited authors)
HILINSKI, E. F., HUPPERT, D., KELLEY, D. F., MILTON, S. V., & RENTZEPIS, P. M.
complete list of authors
HILINSKI, EF||HUPPERT, D||KELLEY, DF||MILTON, SV||RENTZEPIS, PM