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Issue 6, 2012
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The mechanism of the photochromic transformation of spirorhodamines

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Abstract

We investigate the equilibrium, kinetics, and mechanism of the photochromic transformation of a series of amido spirorhodamine compounds—differing in the nature of the substituents of the amido group and in the rhodamine chromophore—in ethanol at room temperature in the presence of trifluoroacetic acid. A proton participates in the equilibrium between the spiro form and the open rhodamine form. The relaxation times in the dark or under continuous irradiation show a linear dependence on the proton concentration. The slopes of these plots show a linear free energy relation with the equilibrium constant of the transformation. A mechanism involving reversible reaction steps between four states: the two thermodynamically stable isomers, a protonated spiro form, and a deprotonated open form, can account for the kinetic observations in the dark and under irradiation.

Graphical abstract: The mechanism of the photochromic transformation of spirorhodamines

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Article information


Submitted
10 Dec 2011
Accepted
26 Mar 2012
First published
26 Apr 2012

Photochem. Photobiol. Sci., 2012,11, 1081-1086
Article type
Paper

The mechanism of the photochromic transformation of spirorhodamines

H. Montenegro, M. Di Paolo, D. Capdevila, P. F. Aramendía and M. L. Bossi, Photochem. Photobiol. Sci., 2012, 11, 1081
DOI: 10.1039/C2PP05402G

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