Issue 28, 2015

A comprehensive spectroscopic investigation of α-(2-naphthyl)-N-methylnitrone: a computational study on photochemical nitrone–oxaziridine conversion and thermal EZ isomerization processes

Abstract

This comprehensive spectroscopic analysis of α-(2-naphthyl)-N-methylnitrone has proposed its photochemical oxaziridine formation and thermal EZ isomerization mechanisms. The activation energy for the conversion of the unstable non-planar E isomer to the stable planar Z-isomer is found to be 23.7 kcal mol−1 at the CASSCF/6-31G* level of calculation. A transition state with a negative frequency of 350 cm−1 is likely to be responsible for this process. Both CASSCF and ONIOM-based studies have revealed that the nitrone–oxaziridine photochemical conversion involves non-radiative decay channels which include biradicaloid conical intersection (CI) points through Hula-twist and terminal one-bond-flip motions, situated at 35–40 kcal mol−1 below the first excited singlet state (S1). Following the directions of their gradient-difference vectors, the optimized oxaziridine geometries are obtained. The nature of the low-lying singlet–singlet transitions of these α-naphthyl N-methylnitrones is found to be similar to that of the conjugated non-polar polyenes, and differs appreciably from our previously studied long-chain conjugated nitrone systems. The fluorescent S1 state with a radiative lifetime of nanosecond order is populated by the weak upward S0–S1 transition (transition moment: 0.3 Debye) and through the decay of the S2 state, which eventually gets involved in the S0/S1 conical intersections.

Graphical abstract: A comprehensive spectroscopic investigation of α-(2-naphthyl)-N-methylnitrone: a computational study on photochemical nitrone–oxaziridine conversion and thermal E–Z isomerization processes

Supplementary files

Article information

Article type
Paper
Submitted
14 Dec 2014
Accepted
17 Feb 2015
First published
18 Feb 2015

RSC Adv., 2015,5, 22148-22159

Author version available

A comprehensive spectroscopic investigation of α-(2-naphthyl)-N-methylnitrone: a computational study on photochemical nitrone–oxaziridine conversion and thermal EZ isomerization processes

P. Saini and A. Chattopadhyay, RSC Adv., 2015, 5, 22148 DOI: 10.1039/C4RA16375C

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