Knowledge Bank

The electronic spectra of several chemical analogues of vitamin $B6$ (namely, salicylaldehyde, salicylaldimine, 3-hydroxy-4-pyridinaldehyde and 3-hydroxy-4-pyridinaldimine) are discussed in the context of all-valence-electron molecular orbital $computations.1$ Specific reference is made to: 1) proton tautomerism induced transition energy and oscillator strength variations; 2) chemical ionization induced variations in state energies and electron densities; 3) theoretical expectations for excited state proton transfer reactions; 4) modulation of fluorescence intensity by low-energy $\sigma \pi \ast (A\prime \prime$) states. On the basis of an analogy between literature spectral data and quantum chemical results, several tentative electronic state identifications are made.