A method for predicting the ground state reduction potentials of organic molecules on the basis of the correlation of computed energy differences between the starting S(0) and one-electron-reduced D(0) species with experimental reduction potentials in acetonitrile has been expanded to cover 3.5 V of potential range and 74 compounds across 6 broad families of molecules. Utilizing the conductor-like polarizable continuum model of implicit solvent allows a global correlation that is computationally efficient and has improved accuracy, with r(2) > 0.98 in all cases and root mean square deviation errors of <90 mV (mean absolute deviations <70 mV) for either B3LYP/6-311+G(d,p) or B3LYP//6-31G(d) with an appropriate choice of radii (UAKS or UA0). The correlations are proven to be robust across a wide range of structures and potentials, including four larger (27-28 heavy atoms) and more conformationally flexible photochromic molecules not used in calibrating the correlation. The method is also proven to be robust to a number of minor student "mistakes" or methodological inconsistencies.

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The spirocyclic oxazinoquinolinespirohexadienone (OSHD) "photochromes" are computationally predicted to be an attractive target as electron deficient analogues of the perimidinespirohexadienone (PSHD) photochromes, for eventual application as photochromic photooxidants. We have found the literature method for their preparation unsuitable and present an alternative synthesis. Unfortunately the product of this synthesis is the long wavelength (LW) ring-opened quinonimine isomer of the OSHD. We have found this isomer does not close to the spirocyclic short wavelength isomer (SW) upon prolonged standing in the dark, unlike other PSHD photochromes. The structure of this long wavelength isomer was found by NMR and X-ray crystallography to be exclusively the quinolinone (keto) tautomer, though experimental cyclic voltammetry supported by our computational methodology indicates that the quinolinol (enol) tautomer (not detected by other means) may be accessible through a fast equilibrium lying far toward the keto tautomer. Computations also support the relative stability order of keto LW over enol LW over SW.

Our undergraduate research group has long focused on the preparation and investigation of electron-deficient analogs of the perimidinespirohexadienone (PSHD) family of photochromic molecular switches for potential application as "photochromic photooxidants" for gating sensitivity to photoinduced charge transfer. We previously reported the photochemistry of two closely related and more reducible quinazolinespirohexadienones (QSHDs), wherein the naphthalene of the PSHD is replaced with a quinoline. In the present work, we report our investigation of the electrochemistry of these asymmetric QSHDs. In addition to the short wavelength and photochromic long-wavelength isomers, we have found that a second, distinct long-wavelength isomer is produced electrochemically. This different long-wavelength isomer arises from a difference in the regiochemistry of spirocyclic ring-opening. The structures of both long-wavelength isomers were ascertained by cyclic voltammetry and 1H NMR analyses, in concert with computational modeling. These results are compared to those for the symmetric parent PSHD, which due to symmetry possesses only a single possible regioisomer upon either electrochemical or photochemical ring-opening. Density functional theory calculations of bond lengths, bond orders, and molecular orbitals allow the rationalization of this differential photochromic vs electrochromic behavior of the QSHDs.