We have investigated the structure and spectra (NMR, UV/visible) of several Yariv reagents and models for these species, using both density functional theory (DFT) and approximate coupled-cluster methods (ADC(2)). We have also studied the formation of dimers and model trimers as a first step to understand the aggregation of these species in aqueous solution. One question that our calculations help resolve is the origin of two strong bands in the visible region of the spectrum: these are confirmed as resulting from enol-keto tautomerism, and are not a result of aggregation, which was a hypothesis that had been advanced previously. The UV/visible spectrum of the Yariv reagents can be explained entirely in terms of tautomerism within a single molecule - no dimers or clusters are involved.
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