PHOTODISSOCIATION OF HALOAROMATICS - DETECTION, KINETICS, AND MECHANISM OF ARYLMETHYL RADICAL FORMATION
Academic Article
Overview
Identity
Additional Document Info
Other
View All
Overview
abstract
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.
