The reversible thermochromic behaviour of homoleptic [{V(OR)(4)}(n)] complexes in solution [R = Pr(i) (product I), Bu(s) (B(s)), Nep (N) and Cy (C)] is accounted for the existence of an aggregation equilibrium involving dimeric and monomeric species in which vanadium(iv) is respectively five- and four-coordinate. Bulky R groups such as Bu(t) and Pe(t) (tert-pentoxide) prevent aggregation and therefore give rise to exclusively mononuclear compounds (B(t) and P(t), respectively) that are not thermochromic. The complexes and their temperature-dependent interconversion were characterised by single crystal X-ray diffractometry, magnetic susceptibility measurements and electronic, FTIR and EPR spectroscopies in a wide temperature range. Equilibrium constants and enthalpy and entropy changes for the dimerization reactions have been determined and compared with literature data.

Two discrete mononuclear complexes, [Tb(bbpen)(NO 3 )] (I) and [Tb(bbppn)(NO 3 )] (II), for which H 2 bbpen = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine and H 2 bbppn = N,N′-bis(2-hydroxylbenzyl)-N,N'-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates II from I and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of H 2 bbppn is described here for the first time, while that of complex II has been redetermined in the monoclinic C2 space group in light of new diffraction data. In II, selective crystallization leads to spontaneous resolution of enantiomeric molecules in different crystals. Absolute emission quantum yields (ϕ) and luminescence excited-state lifetimes (at room temperature and 11 K) were measured for both complexes. Despite their similar molecular structures, I and II exhibit remarkably different ϕ values of 21 ± 2% and 67 ± 7%, respectively, under UV excitation at room temperature. Results of quantum-mechanical (DFT and TD-DFT) calculations and experimental PL measurements also performed for H 2 bbpen and H 2 bbppn confirmed that both ligands are suitable to work as "antennas" for Tb III . Considering the 5 D 4 lifetime profiles and the significantly higher absolute quantum yield of II, it appears that thermally active nonradiative pathways present in I are minimized in II due to differences in the conformation of the ethylenediamine bridge.

Atomic multipoles from the Quantum Theory of Atoms in Molecules(QTAIM), up to quadrupoles, and CHELPG charges are employed in the description of electrostatic properties of some small linear molecules: H 2 , HF, HCl, HBr, HCN, HNC, and CO. A proton is placed on the molecular axis in distances within the range 3-8 Å from the terminal atoms. The polarization of molecular electronic densities induced by the proton is readily included by the calculation of atomic multipoles in each proton-molecule arrangement. Electrostatic potentials at the proton position as given by QTAIM multipoles are always in better agreement with the reference results, calculated directly at the B3LYP/6-311G(3d,3p) level, than those predicted with CHELPG charges, particularly for cases in which QTAIM multipoles showed that the contribution of atomic charges to these potentials is not clearly predominant over other contributions as in H 2 , HCl, HBr, HNC, and CO. The lone pair at the carbon atoms in CO and HNC, as described by QTAIM atomic dipoles, is indispensable in studies of electrostatic properties of these molecules. Moreover, QTAIM multipoles are also able to describe properly the large polarizations induced by the proton along the proton-molecule distances studied.

In this paper we present a method to obtain the electroaffinity and the ionization potential of conjugated polymers via Fowler–Nordheim tunneling current measurements. The method allows the measurement of the electroafinity and ionization potential for a sandwich type device, where the barriers at both sides of the polymer are different. The advantage of this method is that barrier height, the electroaffinity, and the ionization potential are obtained independent of the polymer film thickness and the electron (or hole) effective mass. We have used the proposed methodology to obtain the barrier heights and electroaffinity of poly (p-phenylene-vinylene) (PPV) in Metal/Polymer/Metal sandwich structures. For the present case the electrodes (Al/Au, Al/Ga, Al/In, Al/Sn) used lead only to electron and not hole tunneling current, thus only the electroaffinity has been obtained. The experimental value for the electroaffinity of PPV is of 3.87±0.04 eV.