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The molecular structures of a representative selection of phosphatranes were studied by means of the ab initio MP2 method. The calculated results reasonably matched the available X-ray data. The special properties of the intrabridgehead interaction were described in terms of hybridization, bond order index, force constant, and vibrational frequency. The atom-in-molecules analysis of the electronic charge density showed the presence of a CP(3,−1) betwen the bridgehead centers in the cationic species but not in all of the neutral phosphatranes. The proton affinities of bases with no apical substituent on the phosphorus were accurately calculated for both the gas phase and solution (DMSO). The unique electronic structure of phosphatranes was theoretically investigated by means of their spectroscopic properties. The NMR chemical shifts and indirect nuclear spin−spin coupling constants, computed by DFT-based methods, were fairly consistent with experimental evidence, in particular for the observables involving the central phosphorus. The photoelectron spectrum of azaphosphatrane, having NMe equatorial groups, was interpreted by means of ab initio outer valence Green's function calculations, which gave a consistent reproduction of the energies and splittings of the uppermost bands, associated with the lone pairs of the bridgehead and equatorial heteroatoms. Thus, computations provided reliable predictions of the variations of the NMR parameters and ionization energies with change of the equatorial centers and apical substitution at phosphorus.

The low volatility and thermal instability made the photoelectron (PE), electron transmission (ET), and dissociative electron attachment (DEA) spectroscopy measurements on curcumin (a potent chemopreventive agent) unsuccessful. The filled and empty electronic structure of curcumin was therefore investigated by exploiting the PES, ETS, and DEAS results for representative fragment molecules and suitable quantum-mechanical calculations. On this basis, a reliable pattern of the vertical ionization energies and electron attachment energies of curcumin was proposed. The pi frontier molecular orbitals (MOs) are characterized by sizable interaction between the two phenol rings transmitted through the dicarbonyl chain and associated with a remarkably low ionization energy and a negative electron attachment energy (i.e., a largely positive electron affinity), diagnostic of a stable anion state not observable in ETS. The lowest energy electronic transitions of half-curcumin and curcumin and their color change by alkalization were interpreted with time-dependent density functional theory (DFT) calculations. For curcumin, it is shown that loss of a phenolic proton occurs in alkaline ethanolic solution.

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The low-lying Rydberg and intravalence excited states of formaldehyde, acetaldehyde, and acetone, accessed by multiphoton absorption, have been investigated at ab initio level according to quantum electrodynamical formalisms, by utilizing random-phase-approximation vertical transition energies and amplitudes. For all three carbonyls, two-photon spectroscopic properties which could be detected with various experimental arrangements have been reported. For formaldehyde, an exhaustive overview on spectroscopic observables associated with multiphoton absorption is presented. The transition probability coefficients and polarization ratios for two-, three-, and four-photon single-color absorption from plane polarized, circularly polarized, and unpolarized light have been evaluated. The molecular response to concerted absorption of two and three photons from two laser beams under various polarization conditions has been investigated as a function of the photon energies. An attempt has also been made to estimate the magnitude and direction of the electrochromic changes in two-photon spectroscopic properties brought about by an external static electric field.