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A Novel Technique for Generating and Observing Chemiluminescence in a Biological Setting

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Turning the [Ru(bpy)2dppz]2+ light-switch on and off with temperature.

Matthew K Brennaman¹, James H Alstrum-Acevedo, Cavan N Fleming

¹Venable and Kenan Laboratories, Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

Journal of the American Chemical Society

|December 12, 2002

Summary

Excited-state lifetime measurements reveal the light-switch effect in [Ru(bpy)2dppz](2+) is driven by energy and entropy, not state reversal. This provides a unified understanding of its photophysics across different solvents.

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Area of Science:

Photochemistry
Coordination Chemistry
Spectroscopy

Background:

Ruthenium polypyridyl complexes like [Ru(bpy)2dppz](2+) exhibit unique photophysical properties.
The 'light-switch' effect, where luminescence is enhanced in certain environments, is a key characteristic.
Understanding the excited-state dynamics is crucial for their application.

Purpose of the Study:

To investigate the temperature-dependent excited-state lifetime of [Ru(bpy)2dppz](2+).
To elucidate the photophysical mechanisms underlying the light-switch effect in both protic and aprotic solvents.
To reconcile existing models of excited-state behavior.

Main Methods:

Temperature-dependent excited-state lifetime measurements.
Spectroscopic analysis in various solvent environments (protic and aprotic).

Main Results:

A unifying picture of excited-state photophysics was established, applicable to both solvent types.
Evidence supports the existence of bpy-like and phz-like states linked to the dppz ligand.
The bright state's orbital size is comparable to the (3)MLCT state in [Ru(bpy)3](2+).

Conclusions:

The light-switch effect is not caused by a state reversal.
The dark state remains energetically favored, even in aprotic solvents.
Light-switch behavior arises from a balance between energy favoring the dark state and entropy favoring the bright (bpy) state.