The effect of annulation upon the solvatochromic behaviour of related merocyanines

Abstract

O efeito da anelação em fragmentos aromáticos doadores e/ou aceptores em merocianinas aparentadas é discutido com auxílio de um modelo teórico baseado em cálculos semi-empíricos utilizando o método AM1. As previsões teóricas são validadas com exemplos de oito corantes solvatocrômicos descritos na literatura.The effect of annulation of the donor and/or the acceptor ring fragments of related merocyanines is discussed with the aid of a theoretical model based on semiempirical calculations performed with the AM1 method. The theoretical expectations are validated with examples of eight solvatochromic dyes described in the literature.

Towards a unified view of the solvatochromism of phenolate betaine dyes

“…We had previously drawn attention to the fact that, for a family of merocyanines, increasing annulation of the donor or acceptor fragment had a significant effect on the ground and excited states of the dye, making the former less zwitterionic, and eventually shifting its negative solvatochromism to an inverted behavior 23…”

Thermo‐Solvatochromism of Merocyanine Polarity Probes – What Are the Consequences of Increasing Probe Lipophilicity through Annelation?

“…The contributions of these Lewis structure to the ground states depend on the molecular structures of the dyes, in particular, the number of rings present, and the solvent. [25] These explanations are analyzed below.…”

Environmental updates

“…Structure (a) is easily obtained from optimization of the phenol blue molecular geometry at any level of calculation because it has the lower energy in isolated form. As the structure (b) and the resonant forms can be stabilized by solvent effects, several schemes were used 2, 4, 9, 11 to obtain such charge‐separated structures of many merocyanine dyes.…”

“…This method starts with structure (a) and, as the electric field gets stronger, the molecule approaches structure (b). Another usual scheme 11 consists of placing a positive point charge near the oxygen of phenol blue. Here we have used this scheme.…”