Fluorescence Properties of Thiacarbocyanine Dyes at Low Temperatures

Measurements were carried out for time-resolved fluorescence spectra of dye solutions containing thiacarbocyanine and its derivatives with ethylene and vinylene bridges in the polymethine chain. At low temperature, an additional band appears in the spectrum related to an intramolecular electronic transition. Analysis of the transition lifetimes and a quantum-chemical model indicated that this transition should be attributed to a short-lived asymmetrical component formed along with the symmetrical component upon relaxation of the excited state but not appearing at room temperature due to conformational transformations.