Free rotor styrylcyanine chromogens

• Published in: Laser chemistry 1986, Vol.6 (6), p.381-389
• Main Authors: HABASHY, M. M, ANTONIOUS, M. S, ABDEL-KADER, M, ABDEL-MOTTALEB, M. S. A
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Exact sciences and technology; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Molecular properties and interactions with photons; Physics
• ISSN: 0278-6273; 1476-3516
• DOI: 10.1155/LC.6.381

Fluorescence spectra (maximum wavelength λ F ) and fluorescence quantum yields ( φ F ) were measured for four structurally related styrylcyanine chromogens of the pyridinium and quinolinium type (1–4) in different solvents at ambient temperature and 77 K. The response of λ F and φ F values to changes in solvent polarity, solvent hydrogen bonding donor strength, viscosity and temperature was a sensitive function of chromogen structure. The sensitivities of the λ F and φ F values correlate with the degree of charge transfer character of the S 1, C T state; Stokes shift of fluorescence was progressively decreased while φ F value was enhanced as the CT character of S 1, C T state increases. Moreover, a large edge‐excitation red shift was observed in ethanol glass at 77 K. The dominant photophysical features for these dyes are discussed in terms of strong emission from an intramolecular CT state characterized by different solvation sites indicated by the observation of the excitation‐wavelength dependent phenomenon in ethanol at 77 K and an important non‐radiative decay channel involving rotation of the different parts of molecules leading to a more relaxed weakly fluorescent S 1, C T created in fluid media. The viscosity dependence of fluorescence properties (a marked increase in φ F was observed with increasing viscosity) suggests that these dyes can be useful reporters of microviscosity for different sites in various organized assemblies. Moreover, it was suggested that increasing H‐bonding donor strength of the solvent activates a rotatory non‐radiative decay channel probably by localizing charge densities and decreasing CT nature of the S 1, C T state.