Three-Color Three-Laser Photochemistry of Di(p-methoxyphenyl)methyl Chloride

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Three-color three-laser photochemistry of di( p -methoxyphenyl)methyl chloride (( p -CH 3 OC 6 H 4 ) 2 CHCl = An 2 CHCl) was studied by three-step excitation using 308-, 355-, and 495-nm lasers with delay times of 100 ns to 3 μs. Di( p -methoxyphenyl)methyl radical (An 2 CH • ) was produced together with An 2 CH • in the excited state (An 2 CH • *) and di( p -methoxyphenyl)methyl cation (An 2 CH + ) in quantum yields of 0.09, 0.12, and 0.12, respectively, after a laser flash during 308-nm laser (first laser) photolysis of An 2 CHCl in acetonitrile. Excitation of An 2 CH • with a 355-nm laser (second laser) resulted in formation of transient absorption of An 2 CH • * and An 2 CH + and fluorescence of An 2 CH • * with a peak at 550 nm. The formation of An 2 CH + from An 2 CH • requires two-photon energy at 355 nm and proceeds by resonant two-photon ionization (RETPI) of An 2 CH • through sequential excitation of An 2 CH • *. Excitation of An 2 CH + with a 495-nm laser (third laser) produced fluorescence with a peak at 560 nm. Although the fluorescence of An 2 CH + was also observed without the second laser excitation because of the initial formation of An 2 CH + during the first 308-nm laser photolysis, the fluorescence intensity of An 2 CH + increased approximately 1.2 times with the second 355-nm laser excitation of An 2 CH • . Therefore, the second laser excitation can perform the conversion of An 2 CH • to An 2 CH + through RETPI within the laser flash duration, and the fluorescence intensity of An 2 CH + can be controlled by the second irradiation.