On the solvatochromic reversal of merocyanine dyes. Part 1. The UV–VIS spectroscopic behaviour of vinylogous γ-pyridones

Abstract

A theoretical approach is described t o rationalize and predict the solvatochromic behaviour of vinylogous y-pyridones. The theoretical curves obtained are shown t o reproduce the experimental UV-VIS spectroscopic behaviour of dyes 1, 2, 3 and 5. The model reconciles previous conflicting reports on the solvatochromism of these and related dyes.Solvatochromic dyes generally exhibit steady bathochromic (positive solvatochromism) or hypsochromic shifts (negative solvatochromism) in solution, as polarity of the medium is increased. Some dyes may change their behaviour in solution with a change of solvent, and revert the sign of their solvatochromic shifts at a given polarity. Compound 1 is generally Paper 4/05332J

Synthesis and Solvatochromism of Substituted 4-(Nitrostyryl)phenolate Dyes

“…In general, the solvatochromic dyes exhibiting negative solvatochromism have an electron-donor phenolate group in their molecular structure and a pyridinium center as the electron-acceptor group. [10][11][12][13][14][15][16][17][18][19][20][21][22] Recently, the solvatochromism of nitro-substituted benzylideneaminophenolates was investigated by also carried out in order to verify the contribution of various solvent parameters to the solvatochromism exhibited by the probes. 3a, b 4a, b 5a, b 6a, b 7a, b 8a, b 9a through condensation reactions have been reported in the literature.…”

Photophysical properties of a surfactive long-chain styryl merocyanine dye as fluorescent probe

“…Such type of solvatochromism is detected in polymethine dye chromophores, which can reach the ideal polymethine state in weakly polar solvent [61]. Similar phenomena have been observed for other dyes also [62][63][64][65], where the replacement of solvents with low polarity by highly polar solvent, or vice versa, leads to a deviation from the ideal polymethine state and changes the energy of the electronic transition.…”

The effect of annulation upon the solvatochromic behaviour of related merocyanines

“…However, contrary to other treatments which tried to interpret the solvatochromic behaviour of a given dye by calculation of its properties in a few different media only 3,5,6 , we emphasized the need of calculating its properties in several environments of changing polarities. Though based on a simplified theoretical model, the results of such calculations have been successfully compared with qualitative trends exhibited by a family of related pyridinium phenoxides 2 , and in comparing the solvatochromic behaviour of a previously described vinylogous γ-pyridone with its α-analogue synthesized by us 7 .…”

“…However, by emphasizing trends, instead of par- We have adopted this second approach in the study of the solvatochromic behaviour of merocyanines. Our approach was based on the influence of an external electric field upon the geometry and electronic levels of a given dye 2 . It was also related to other proposals in the literature for the treatment of the spectra 3 , polarizabilities and hyperpolarizabilities of merocyanines 4 .…”