Synthesis, characterization and spectral properties of new, highly fluorescent, 4-hydroxythiazoles. (May 2016)

• Record Type: Journal Article
• Authors: Kammel, Richard; Tarabová, Denisa; Machalický, Oldřich; Nepraš, Miloš; Frumarová, Božena; Hanusek, Jiří
• Is Part Of: Dyes and pigments. Volume 128(2016)
• Page Start: 101
• Page End: 110
• Publication Date: 2016-05
• Subjects: 4-Hydroxythiazoles -- Synthesis -- Absorption spectra -- Fluorescence quantum yields -- Quantum chemical calculations -- Intramolecular hydrogen bond; Dyes and dyeing -- Periodicals; Pigments -- Periodicals; 667.2
• DOI: 10.1016/j.dyepig.2016.01.017
• Languages: English
• ISSNs: 0143-7208

Abstract

Abstract: Eight substituted 2-aryl-4-hydroxy-5-(2′-hydroxyphenyl)-1, 3-thiazoles have been prepared and their fluorescence properties have been investigated under neutral and alkaline conditions in solutions of various organic solvents. From the comparison with analogous 4-hydroxy-2, 5-diphenyl-1, 3-thiazole it is clear that both in neutral as well as in the deprotonated state the presence of the 2′-hydroxy group substantially (2–4 times) enhances fluorescence quantum yields ( Φ ) – most probably due to formation of an intramolecular hydrogen bond. Introduction of an electron withdrawing substituent into the 2-aryl group (2-pyridyl and 4-trifluormethylphenyl derivatives) further enhances Φ up to 0.93 (in dioxane). Upon deprotonation of the 4-hydroxy group a large bathochromic shift of the absorption (Δ λ max ≈ 70 nm) as well as emission (Δ λ em ≈ 110 nm) bands occurs and the Φ -s are typically between 0.3 and 0.7. On the basis of quantum chemical calculations and spectral results, a hydrogen bond interaction between two hydroxyl groups is obvious. The first absorption band of all studied compounds corresponds to π–π* HOMO–LUMO transition possessing a CT character. Graphical abstract: Highlights: Highly fluorescent 2-aryl-4-hydroxy-5-(2′-hydroxyphenyl)-1, 3-thiazoles were prepared. The presence of 2′-hydroxyphenyl group enhances fluorescence quantum yields. Quantum calculations prove existence of the intramolecular hydrogen bond. Quantum calculations prove π–π* HOMO–LUMO S0 –S1 transition having CT character.