Journal of Photochemistry and Photobiology A: Chemistry 163 (2004) 497–501 Effect of viscosity and temperature on some photophysical parameters of 9-phenyl-10-methoxy anthracene Samy A. El-Daly a,∗ , El-Zeiny M-Ebeid a , A.S. Babaqi b , Sadak M. Al-Hazmy b a Chemistry Department, Faculty of Science, Tanta Uuiversity, Tanta, Egypt b Chemistry Department, Faculty of Science, Sanaa University, Sanaa, Yemen Received 7 January 2004; accepted 30 January 2004 Abstract 9-Phenyl-10-methoxy anthracene (PMA) shows no significant change in the absorption spectrum on going from non-polar to polar solvents, indicating no change in dipole moment of dye molecules upon excitation. The fluorescence quantum yields (Φ f ) of PMA have been measured in different solvents. It was found that Φ f and the lifetime (τ f ) increases with increasing the viscosity of solvent. It was also found that the fluorescence quantum yields (Φ f ) increased sharply by lowering the temperature. The quenching rate constants by molecular oxygen were measured using lifetime measurements. © 2004 Elsevier B.V. All rights reserved. Keywords: 9-Phenyl-10-methoxy anthracene; Fluorescence; Lifetime; Quantum yield; Quenching by oxygen 1. Introduction Anthracene derivatives show high fluorescence quantum yield (Φ f ) and smaller fluorescence lifetimes than unsubsti- tuted anthracene, consequently some of these molecules are used in scintillators and in dye laser as active media [1]. On the other hand there are some of anthracene derivatives char- acterized by very weak or practically absence of fluorescence [2–7] which can provide more information about the path- ways which absorbed excitation energy is dissipated than can highly fluorescent molecules. The photostability and pho- tophysical properties of anthracene derivatives varied from one to another according to the molecular structure and the positions of the substituents as well as the viscosity and temperature of the medium [8–10]. In the present article we study the photophysical behavior of 9-phenyl-10-methoxy anthracene (PMA) in different media. The effect of medium viscosity and temperature were also studied. 2. Experimental 9-Phenyl-10-methoxy anthracene was kindly provided by professor E. Daltrozzo, Faculty of Chemistry, Univer- ∗ Corresponding author. Present address: Chemistry Department, Faculty of Science, Taiz University, P.O. Box 1003, Taiz, Yemen. E-mail address: samyeldaly@yahoo.com (S.A. El-Daly). sity of Konstanz, Germany. Steady-state fluorescence was measured using a Shimadzu RF 510 Spectrofluoropho- tometer with band pass of 10 nm using a right-angle ar- rangement. The fluorescence spectra were corrected for the machine response using 10 -5 mol dm -3 anthracene solution in benzene as reported earlier by Melhuish [11]. UV-Vis absorption spectra were recorded on Shimadzu UV-160 A Spectrophotometer with band pass of 5 nm. Flu- orescence quantum yields (Φ f ) were measured relative to 9,10-diphenylanthracene as a reference standard [12]. Low sample concentrations (≤0.1 absorbance units) were used to avoid reabsorption. The following relation has been ap- plied to calculate the fluorescence quantum yields relative to those of 9,10-diphenylanthracene Φ f (s) Φ f (r) =  I s (ν ′ ) dν ′  I r (ν ′ ) dν ′ A r n 2 s A s n 2 r The integrals represent the corrected fluorescence peak ar- eas. A is the absorbance at the excitation wavelength, n is the refractive index of the solvent used. The subscript ‘s’ and ‘r’ refer to sample and reference, respectively, The fluorescence lifetime measurements were based on the time-correlated single-photon counting technique (TCSPC). The decay curves were analyzed using the method of itera- tive, nonlinear least squares [10]. The experimental details and the method of analysis are similar to those described in Ref. [13]. The lifetimes in the presence of oxygen were mea- sured for aerated solutions in which oxygen concentration 1010-6030/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jphotochem.2004.01.020