Solvent Effect on the Deactivation Processes of Benzophenone Ketyl Radicals in the Excited State

Abstract

The solvent effects on ketyl radicals of benzophenone derivatives (BPD) in the excited state (BPDH*(D1)) were investigated. Absorption and fluorescence spectra of BPDH*(D1) in various solvents were measured using nanosecond-picosecond two-color two-laser flash photolysis. The fluorescence peaks from BPDH*(D1) showed a shift due to the dipole-dipole interaction with the solvent molecules. The dipole moments (mu(e)) of BPDH*(D1) were estimated to be 7-10 D, indicating that BPDH*(D1) are highly polarized. It was revealed that the fluorescence lifetime (tau(f)) depends on mu(e) in acetonitrile because the stabilization by solvent molecules affects the tau(f) value in polar solvents, predominantly. On the contrary, the conformation of BPDH*(D1) plays an important role in cyclohexane because the efficiency of the unimolecular reaction from BPDH*(D1) depends on the conformation. The substituent effect on the electron transfer from BPDH*(D1) to their parent molecules was also discussed.

Reactions of excited-state benzophenone ketyl radical in a room-temperature ionic liquid

“…In contrast, the photo-excitation of BPH in polar solvents is known to lead to the formation of solvated electrons. [43][44] In the present study we found no experimental evidence for the formation of solvated electrons in Bmim-TFSA. Even if an electron had been ejected from BPH, the electron would have immediately been scavenged by the Bmim cation, as we previously reported.…”

Photochemistry for the Synthesis of Noble Metal Nanoparticles

“…The diphenylmethanol cation quickly deprotonates to regenerate MeOBP (state f). 99,120,122,132134 In the presence of an appropriate electron acceptor, the formed MePI…”

Influence of the chloro substituent position on the triplet reactivity of benzophenone derivatives: a time‐resolved resonance Raman and density functional theory study

“…The reaction details and properties of the excited states of BP and its derivatives have been revealed extensively through the broad application of various time‐resolved spectroscopies, especially transient absorption (TA). For example, the properties and reaction mechanisms of the ketyl radical and the radical from the solvent and their reaction to produce a light absorbing transient (LAT) have been reported . The intersystem crossing from S 1 to T 1 for BP and its derivatives has been observed directly by ultrafast TA with measured rates of ~10 11 s –1 , and a rapid water addition process to the protonated BP triplet was identified to result in the fast deactivation of the triplet BP in acidic aqueous solution .…”

“…The photoreduction of aromatic ketones especially benzophenone (BP) and its derivatives has received much attention over the years and a number of studies have been reported. [1][2][3][4][5][6][7][8][9][10]13,27,31,33] It is well-known that the hydrogen abstraction reaction of BP and its derivatives typically arises from their np* excited triplet state that can react with a hydrogen donor molecule to produce a corresponding ketyl radical and free radical of the hydrogen donor molecule. This kind of reaction may proceed by either a direct hydrogen atom transfer or a coupled electron/proton transfer.…”