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Halogen-Bond Assisted Photoinduced Electron Transfer.

Bogdan Dereka¹, Ina Fureraj¹, Arnulf Rosspeintner¹

¹Department of Physical Chemistry, University of Geneva, CH-1211 Geneva, Switzerland.

Molecules (Basel, Switzerland)

|December 5, 2019

Summary

Electron transfer quenching in excited states is slower with halogen-bond (XB) compounds than expected. This indicates that electron transfer occurs specifically upon halogen bond formation, revealing a strong orientational constraint.

Keywords:

excited-state dynamics photochemistry time-resolved fluorescence ultrafast IR spectroscopy

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Area of Science:

Photochemistry
Supramolecular Chemistry
Electron Transfer Dynamics

Background:

Halogen bonding (XB) complexes in excited states can undergo ultrafast decay.
This decay is often attributed to electron transfer quenching by XB donors.

Purpose of the Study:

To investigate the mechanism of excited-state quenching by XB compounds.
To compare quenching dynamics with XB compounds versus a non-halogenated electron acceptor.

Main Methods:

Studied excited-state (S1) quenching dynamics of a dye using iodo-compounds in inert solvents.
Compared results with quenching by fumaronitrile, a non-halogenated acceptor.
Applied Smoluchowski-Collins-Kimball analysis to excited-state population decays.

Main Results:

Quenching by XB compounds was slower than diffusion-controlled, despite a larger driving force.
Intrinsic quenching rate constant and quenching radius were significantly smaller with XB compounds.
Stronger orientational constraints were observed for quenching with XB compounds.

Conclusions:

Electron transfer quenching with XB compounds is limited by orientational constraints.
The findings suggest that electron transfer is coupled to halogen bond formation.
This provides mechanistic insight into excited-state quenching in XB complexes.