Spectral properties of (5-Phenyl-1,3,4-oxadiazol-2-yl)-7-hydroxycoumarin (POHC)

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Vol. 56; no. 9; pp. 1773 - 1780
• Main Authors: Al-Hazmy, Sadiq M., Kassab, Kawthar N., El-Daly, Samy A., Ebeid, El-Zeiny M.
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 01.08.2000
• Subjects: Coumarin; Coumarins - chemistry; Energy Transfer; Oxadiazoles - chemistry; Oxygen - chemistry; Oxygen quenching; Solvents - chemistry; Spectral properties; Spectrometry, Fluorescence - methods; Spectrophotometry, Atomic - methods; Coumarin; Energy transfer; Spectral properties; Oxygen quenching
• ISSN: 1386-1425
• DOI: 10.1016/S1386-1425(00)00231-6

The electronic absorption, emission and excitation spectra of POHC were measured in different solvents and are affected by solvent polarity. The fluorescence quantum yield of POHC decreases with increasing Richardt and Dimorth solvent parameter ( E T) value of the solvent. In dilute solutions POHC is almost totally present in its protonated nitrogen tautomer form. The deprotonation is a reversible process. A shoulder in the absorption spectra at ≈473 nm indicates the presence of a portion of the tautomer (s) that disappears on lowering the temperature. Molecular oxygen acts as a quencher with quenching rate constant of 1.8×10 10 M −1 s −1 in DMF. Energy transfer from POHC to rhodamine 6G in ethanol was also studied. POHC is relatively photostable in ethanol ( φ c≈1.7×10 −4). Quantum chemical calculations were carried out and correlated to experimental observations.