Challenges to computational quantum chemistry from contemporary advances in polyatomic molecular electronic spectroscopy

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Abstract
Molecular electronic spectroscopy featuring intramolecular proton transfer and twisted intramolecular charge transfer poses a whole new range of problems for computational quantum chemistry. The development of the four‐level laser based on the intramolecular proton‐transfer focuses on the subtleties of the interaction of the singlet and triplet electronic state manifolds of the two different tautomeric species. Examples are given of the sensitive variation of proton‐transfer fluorescence with chemical substitution. A competing excitation channel is shown to exist when internal molecular torsion couples with sudden polarization to yield a twisted intramolecular charge transfer configuration. In such systems, three competing fluorescences can be observed. Several electronic puzzles will be presented that can provide fertile territory for quantum chemical computations. © 1993 John Wiley & Sons, Inc.