Substituent effect on the photoreduction kinetics of benzophenone

A. Demeter, Klaudia Horváth, Katalin Böor, Laura Molnár, T. Soós, G. Lendvay

Research output: Article

12 Citations (Scopus)

Abstract

The kinetics of the photoreduction of four benzophenone derivatives by isopropyl alcohol was examined in acetonitrile, namely, tetra-meta- trifluoromethyl-, di-para-trifluoromethyl-, di-para-methoxy benzophenone, and, for comparison, the unsubstituted molecule itself. The basic spectroscopic (absorption and phosphorescence spectra) and photophysical (quantum yields and excited state energies) properties were established, and the key kinetic parameters were determined by the laser flash photolysis transient absorption technique. The rate coefficients of both the primary and secondary photoreduction reaction show remarkable dependence on ring substitution. This substantial effect is caused by the considerable change in the activation energy of the corresponding process. The experimental results as well as DFT quantum chemical calculations clearly indicate that these benzophenone derivatives all react as n-π* excited ketones, and the rate as well as the activation energy of the reduction steps change parallel with the reaction enthalpies, the determining factor being the stability of the forming aromatic ketyl radicals. The secondary photoreduction of benzophenones by the aliphatic ketyl radical formed in the primary step occurs via a hydrogen bonded complex. The binding energy of the hydrogen bonded complex between the aliphatic ketyl radical reactant and a solvent molecule is a critical parameter influencing the observable rate of the secondary photoreduction.

Original languageEnglish
Pages (from-to)10196-10210
Number of pages15
JournalJournal of Physical Chemistry A
Volume117
Issue number40
DOIs
Publication statusPublished - okt. 10 2013

Fingerprint

photochemical reactions
Kinetics
Hydrogen
kinetics
Benzophenones
Activation energy
Derivatives
Phosphorescence
Molecules
2-Propanol
Photolysis
Quantum yield
activation energy
Ketones
Binding energy
Kinetic parameters
Excited states
Discrete Fourier transforms
isopropyl alcohol
Enthalpy

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Substituent effect on the photoreduction kinetics of benzophenone. / Demeter, A.; Horváth, Klaudia; Böor, Katalin; Molnár, Laura; Soós, T.; Lendvay, G.

In: Journal of Physical Chemistry A, Vol. 117, No. 40, 10.10.2013, p. 10196-10210.

Research output: Article

Demeter, A. ; Horváth, Klaudia ; Böor, Katalin ; Molnár, Laura ; Soós, T. ; Lendvay, G. / Substituent effect on the photoreduction kinetics of benzophenone. In: Journal of Physical Chemistry A. 2013 ; Vol. 117, No. 40. pp. 10196-10210.
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