On the origin of the anomalous ultraslow solvation dynamics in heterogeneous environments

Journal of Chemical Sciences

Kankan Bhattacharyya1²  Biman Bagchi2¹ 

[1] Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012$$;Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032$$

关键词: Ultraslow solvation dynamics;    heterogeneous environments;    polar probe.;   

DOI  :  

来源: Indian Academy of Sciences

【 摘 要 】

Many recent experimental studies have reported a surprising ultraslow component (even >10 ns) in the solvation dynamics of a polar probe in an organized assembly, the origin of which is not understood at present. Here we propose two molecular mechanisms in explanation. The first one involves the motion of the `buried water’ molecules (both translation and rotation), accompanied by cooperative relaxation (‘local melting’) of several surfactant chains. An estimate of the time is obtained by using an effective Rouse chain model of chain dynamics, coupled with a mean first passage time calculation. The second explanation invokes self-diffusion of the (di)polar probe itself from a less polar to a more polar region. This may also involve cooperative motion of the surfactant chains in the hydrophobic core, if the probe has a sizeable distribution inside the core prior to excitation, or escape of the probe to the bulk from the surface of the self-assembly. The second mechanism should result in the narrowing of the full width of the emission spectrum with time, which has indeed been observed in recent experiments. It is argued that both the mechanisms may give rise to an ultraslow time constant and may be applicable to different experimental situations. The effectiveness of solvation as a dynamical probe in such complex systems has been discussed.

【 授权许可】

Unknown