Fluorescence Quenching of UVITEX‐OB by Aniline in Alcohols and Alkanes

Abstract

Fluorescence quenching of UVITEX‐OB [2,5‐thiophenediylbis(5‐tert‐butyl‐1,3‐benzoxazole)] by aniline in different polar and nonpolar solvents was examined at room temperature by steady‐state fluorescence measurements. Positive deviations from the nonlinear Stern–Volmer plots were observed in most of the solvents indicating the extent of quenching to be large. The quencher concentration dependence data were analyzed using ground‐state complex and sphere of action static quenching models in order to interpret the results. The magnitudes of the quenching rate parameters suggest that a sphere of action static quenching model is expected to describe the data most accurately. Also, the results are suggestive of both static and dynamic quenching processes being responsible for the observed positive deviation in the Stern–Volmer plot. Experimental results are described by an equation derived using the finite sink approximation model, which allows the evaluation of diffusion‐limited interaction and the estimation of encounter distance and mutual diffusion coefficient independently.

Keywords:

• Activation energy controlled rate constant (k _a )
• diffusion limited (D)
• finite sink approximation model (FSA)
• fluorescence quenching (Q)
• quenching rate constant (k _d )
• static and dynamic quenching
• Stern–Volmer plot
• UVITEX‐OB (U‐OB)

Acknowledgments

One of the authors (J.R.M.) thanks the UGC, New Delhi, for a fellowship under its DSA Programme (Phase III). The authors are grateful to Reinard of Ceba Speciality Chemicals for the generous gift of UVITEX‐OB sample and to Prof. P. Ramamurthy, National Centre for Ultrafast Processes, Chennai, for extending the TCSPC facility.