Upper Excited State Photochemistry: Solution and Gas Phase Photochemistry and Photophysics of 2- and 3-Cyclopropylindene1

Abstract

The cyclopropylcarbinyl radical rearrangement has been used to probe the photochemistry and photophysics of S2 and S1 in 2-cyclopropylindene (2CPI) and 3-cyclopropylindene (3CPI). Studies in solution and the gas phase are described. Population of S2 with 254 nm light excitation in the gas phase produces the anticipated ring expansion products 2,3,3a,8-tetrahydrocyclopenta[a]indene (1, Φ1 = 0.1) and 1,3,3a,8-tetrahydrocyclopenta[a]indene (2, Φ2 = 0.06) from 2CPI and 3CPI, respectively (Scheme 3). Direct excitation into the S2 state (254 nm) of 2CPI in solution also produces compound 1. The efficiency of the solution phase chemistry is a function of excitation wavelength (Φ1 = 0.022 and 0.006 for 254 and 280 nm, respectively). The solution phase excitation spectrum of 2CPI shows an anomalous dependency on monitoring wavelength which is attributed to a conformational equilibrium. The S1 singlet lifetimes of the cyclopropylindenes are quite short (0.39 and 1.0 ns for 2CPI and 3CPI, respectively) relative to t...