Photochemistry of Benzophenone in Solution: A Tale of Two Different Solvent Environments.

A long-standing ambition of photochemists is to excite species selectively in a complex liquid solution and in turn instigate a controlled chemical reaction. Benzophenone (Bzp) has been studied over six decades as a model system for understanding the photophysics and photochemistry of organic chromophores. Herein, we exploit the red-edge excitation effect to demonstrate that by subensemble selective excitation of Bzp molecules, either coordinated or noncoordinated to phenol through hydrogen bonding in a dichloromethane solution, the rate of an H atom abstraction reaction can be accelerated by a factor of ∼40. To this end, we have employed femtosecond time-resolved electronic and vibrational absorption spectroscopy in conjunction with DFT/TD-DFT calculations. The outcomes have implications for deductions drawn from single-excitation-wavelength studies of the photochemistry of similar molecular systems and especially of charge-transfer chromophores.