Unsymmetrical Relaxation Paths of the Excited States in Cyanine Dyes Detected by Time-Resolved Fluorescence:Polymethinic and Polyenic Forms

Novel applications of organic dyes and vast opportunities for their molecular tailoring keep focus of scientific community on the issues of symmetry breaking in the systems having different location of uncompensated charge, which has tremendous impact on photoluminescent properties of the dyes. In this paper, we provide distinctive experimental evidences of three relaxation paths (one symmetrical and two unsymmetrical) of excited states by analysis of lifetime and spectra of time-resolved fluorescence at low temperature with strong support of quantum-chemical modeling. Importantly, the studied cyanine dye (astraphloxin) in aqueous solution has two different unsymmetrical relaxation paths of excites states in the polymethinic and donor-acceptor polyenic forms, where the last form strongly diminishes in less polar media. The experimental and computational results provide essential fundamental knowledge of molecular electronic relaxations substantially affected by matrix rigidity and polarity for design and photonic applications of elongated π-electronic systems