Optical and Electron Paramagnetic Resonance Studies of the Excited States of 4-tert-Butyl-4′-Methoxydibenzoylmethane and 4-tert-Butyl-4′-Methoxydibenzoylpropane

By Azusa Kikuchi, Nozomi Oguchi, Mikio Yagi

May 22, 2018

  • Year

  • Technique

  • Industry

Title

Optical and Electron Paramagnetic Resonance Studies of the Excited States of 4-tert-Butyl-4′-Methoxydibenzoylmethane and 4-tert-Butyl-4′-Methoxydibenzoylpropane

Author

Azusa Kikuchi, Nozomi Oguchi, Mikio Yagi

Year

2009

Journal

Journal of Physical Chemistry A

Abstract

The excited states of 4-tert-butyl-4′-methoxydibenzoylmethane (BM-DBM) and 4-tert-butyl-4′-methoxydibenzoylpropane (BM-DBP), the model of the keto form of BM-DBM, have been studied through measurements of UV absorption, fluorescence, phosphorescence, and electron paramagnetic resonance spectra in ethanol at 77 K. The energy levels and lifetimes of the lowest excited triplet (T1) states of BM-DBP, dibenzoylpropane (DBP), the model of the keto form of dibenzoylmethane (DBM), and the keto and enol forms of BM-DBM and DBM were determined. The energy level of the T1 state of the keto form is much higher than that of the enol form in BM-DBM. The effect of tautomerization on the T1 lifetime is small in DBM but large in BM-DBM. The methoxy and tert-butyl groups play an important role in lengthening the T1lifetimes of BM-DBP and the keto form of BM-DBM. The nature of the T1 states of the keto and enol forms of BM-DBM can be explained in terms of the mixing of the 3nπ* and 3ππ* states. The observed energy levels and the lifetimes of the T1 states of the UV absorbers provide a useful suggestion for designing more photostable UV absorbers.

Full Article

http://pubs.acs.org/doi/abs/10.1021/jp905236m

Instrument

FP-6500

Keywords

Fluorescence, Phosphorescence, Organic chemistry