Excited state intramolecular charge transfer reaction in non-aqueous reverse micelles: Effects of solvent confinement and electrolyte concentration

Journal of Chemical Sciences

Harun Al Rasid Gazi¹  Ranjit Biswas1¹  Tuhin Pradhan¹  Biswajit Guchhait¹ 

[1] Department of Chemical, Biological and Macromolecular Sciences, and Unit for Nanoscience and Technology, S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700 098, India$$

关键词: Intramolecular charge transfer reaction;    non-aqueous reverse micelles;    confinement effects;    static and dynamic solvent control.;   

DOI  :  

来源: Indian Academy of Sciences

【 摘 要 】

Steady state and time resolved fluorescence emission spectroscopy have been employed to investigate the effects of solvent confinement and electrolyte concentration on excited state intramolecular charge transfer (ICT) reaction in 4-(1-pyrrolidinyl) benzonitrile (P5C), 4-(1-piperidinyl) benzonitrile (P6C), and 4-(1-morpholenyl) benzonitrile (M6C) in AOT/n-heptane/acetonitrile and AOT/n-heptane/methanol reverse micelles. Dramatic confinement effects have been revealed via a huge reduction (factor ranging between 100 and 20) over bulk values of both equilibrium and reaction rate constants. A strong dependence on the size of the confinement (𝑊𝑠) of these quantities has also been observed. 𝑊𝑠 dependent average static dielectric constant, viscosity and solvation time-scale have been determined. Estimated dielectric constants for confined methanol and acetonitrile show a decrease from the respective bulk values by a factor of 3-5 and viscosities increased by a factor of 2 at the highest 𝑊𝑠 considered. Addition of electrolyte at 𝑊𝑠 = 5 for acetonitrile is found to produce a linear increase of confined solvent viscosity but leads to a non-monotonic electrolyte concentration dependence of average solvation time. Reaction rate constant is found to decrease linearly with electrolyte concentration for P5C and P6C but non-monotonically for M6C, the highest decrease for all the molecules being ∼ 20% over the value in the absence of added electrolyte in the solvent pool. The observed huge reduction in reaction rate constant is attributed to the effects of decreased solution polarity, enhanced viscosity and slowed-down solvent reorganization of the solvent under confinement in these non-aqueous reverse micelles.

【 授权许可】

Unknown