Modulation of the ESIPT Emission of Benzothiazole Type Dye Incorporated in Silica-Based Hybrid Materials

• Published in: Langmuir Vol. 25; no. 22; pp. 13219 - 13223
• Main Authors: Grando, Sílvia R, Pessoa, Carolina M, Gallas, Márcia R, Costa, Tania M. H, Rodembusch, Fabiano S, Benvenutti, Edilson V
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 17.11.2009
• Subjects: Chemistry; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Materials: Nano-and Mesostructured Materials, Polymers, Gels, Liquid Crystals, Composites; Surface physical chemistry; Binary compound; Dyes; Hybrid material; Fluorescence; Hydrophobicity; Precursor; Silica; Methyl group; Polarity; Stokes shift; Hydrocarbon; Proton transfer; Replacement; Condensed benzenic compound; Equilibrium; Steady state; Wavelength; Infrared spectrometry; Solid state; Pyrene; Fluorophore; Sol gel process; Isotherm; Environment; Hydrogen bond
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la902242y

A set of silica-based hybrid material samples was obtained, with different molar fractions of tetraethylorthosilicate and dimethyldimethoxysilane, as inorganic and organic sol−gel precursors, respectively. The hybrid material was used as a matrix to disperse the 2-(4′-amino-2′-hydroxyphenyl)benzothiazole, a fluorophore with large Stokes shift caused by an excited state intramolecular proton transfer phenomena (ESIPT). UV−vis and steady-state fluorescence in the solid state were applied in order to characterize the photophysical behavior of the dye. The set of samples was characterized by infrared spectroscopy, elemental analysis, and N2 isotherms. The fluorescent pyrene dye was used as a probe for local polarity environment. For the first time, a modulation in the ESIPT fluorescence emission was achieved, being correlated to the methyl organic content of the hybrid matrix. The equilibrium between the conformers in the ground state is affected by changes in the matrix hydrophobicity. The replacement of silanol groups by methyl groups on matrix surface decreases the hydrogen bond capacity with the dye stabilizing the ESIPT conformer, in spite of the normal conformers, which will present a short wavelength emission band.