A class of fluorescent heterocyclic dyes revisited: photophysics, structure, and solvent effects

Using new solvatochromic parameters to investigate dye–solvent interactions

Solvatochromic behaviours of triazine substituted dyes were evaluated using a novel approach derived from the red shift index (RsI) and associated solvation energy (ASE). These parameters were used to describe the solvation trends of the dye–solvent interactions based on their polarity changes. The concept demonstrates the effect of substituent changes on the triazine scaffold and the induced solvent polarity changes as solvated dyes go through the HOMO–LUMO (highest occupied molecular orbital-lowest uncopied molecular orbital) phases. Primarily, these phases were characterised by evaluating the wavelength of the absorption and emission spectra in different solvents, which, in conjunction with the recently reported computational approaches, provides a well-adjusted model for predicting spectra polarity changes between the dye (solute) and the solvent. Based on the results from this study, predictive polarity changes on the triazine scaffold in different solvents can be empirically monitored both in ground and excited states. Moreover, the solvatochromic parameters can be extended to evaluate the predictive behaviours of different spectra dyes.

A Computational Comparative Study for the Spectroscopic Evaluation of Triazine Derivative Dyes in Implicit Solvation Model Systems Using Semi-Empirical and Time-Dependent Density Functional Theory Approaches

The spectroscopic data for a range of cyclopenta-[d][1,2,3]-triazine derivative dyes have been evaluated using various standard computational approaches. Absorption data of these dyes were obtained using the ZINDO/S semi-empirical model for vertical excitation energies of structures optimised with the AM1, PM3, and PM6 methods. These studies were conducted under vacuum and solution states using the polarisation continuum model (PCM) for implicit solvation in the linear response model. The accuracy, along with the modest computational costs of using the ZINDO/S prediction, combined with the PM3 optimisation method for absorption data was reliable. While a higher computational cost is required for the time-dependent density functional theory (TDDFT), this method offers a reliable method for calculating both the absorption and emission data for the dyes studied (using vertical and adiabatic excitation energies, respectively) via state-specific solvation. This research demonstrates the potential of computational approaches utilising solvation in evaluating the spectroscopic properties of dyes in the rational design of fluorescent probes.