The Chemistry and Physics of Charge-Resonance

Dr Seth Olsen

School of Mathematics and Physics, The University of Queensland

3:35 pm Friday, 22 June 2012, EN103 Lecture Theatre (EN Building), Hawthorn.

Organic dyes with a charge-resonant electronic structure (for example, Michler's Hydrol Blue, below) are venerable molecules, having played a critical role in the development of the synthetic chemical industry. More recently, they have attracted attention because the environmental sensitivity of their optical response makes them useful as molecular sensors and markers. The fluorescence quantum yield of dyes can be modulated over six orders of magnitude in different environments. Large variations in the nonlinear optical response are also observed.
In my talk, I will discuss the chemical and physical concepts underlying the notion of charge-resonance, and describe its mathematical formulation. I will show explicitly that relatively simple 2- and 3- state models based on these concepts can be used to understand and even predict the results of quite complicated and high-level computational quantum chemistry calculations. I will show that models based on the concept of resonating charge forms, which were originally designed to model the color of dye molecules, can also be applied to understand apparently unrelated properties e.g. their nonlinear optical response and also their nonradiative decay behavior. These properties are important to understanding the use of these dyes in several very recent applications, which I will also discuss.

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