Molecular Origins of Dye Aggregation and Complex Formation Effects in Coumarin 343

Solvent effects have a significant impact upon the optoelectronic properties of coumarin 343, which are mainly exploited in the solution phase for a diverse range of applications, including lasers and dye-sensitized solar cells. The influence of solvation on the structure–property relationships for coumarin 343 are analyzed herein using (time-dependent) density functional theory (DFT/TD-DFT) based quantum calculations, in conjunction with UV–vis absorption and 1H NMR spectroscopic measurements. Specifically, these solvent effects on the peak UV–vis absorption wavelengths (λmaxabs), and molecular geometry changes of coumarin 343 are investigated. Coumarin 343 is shown to be prone to dye aggregation; its different molecular aggregation phases, UV–vis absorption profiles, and formation mechanisms are discussed using three representative solvents: cyclohexane [nonpolar and non-hydrogen bonding (NHB)], benzene (polar and nearly NHB), and ethanol (polar and hydrogen-bond accepting/donating). It is also demonstr...