• Energy Research

Fast and efficient intramolecular energy transfer takes place in the umbelliferone–alizarin bichromophore; the process is well described by the Förster mechanism.

UV-vis spectra of anionic ibuprofen and naproxen in a model lipid bilayer of the cell membrane are investigated using computational techniques in combination with a comparative analysis of drug spectra in purely aqueous environments. The simulations aim at elucidating the intricacies behind the negligible changes in the maximum absorption wavelength in the experimental spectra. A set of configurations of the systems constituted by lipid, water, and drugs or just water and drugs are obtained from classical Molecular Dynamics simulations. UV-vis spectra are computed in the framework of atomistic Quantum Mechanical/Molecular Mechanics (QM/MM) approaches together with Time-Dependent Density Functional Theory (TD-DFT). Our results suggest that the molecular orbitals involved in the electronic transitions are the same, regardless of the chemical environment. A thorough analysis of the contacts between the drug and water molecules reveals that no significant changes in UV-vis spectra are a consequence of ibuprofen and naproxen molecules being permanently microsolvated by water molecules, despite the presence of lipid molecules. Water molecules microsolvate the charged carboxylate group as expected but also microsolvate the aromatic regions of the drugs.

AbstractIn this work, the dynamics of electronic energy transfer (EET) in bichromophoric donor–acceptor systems, obtained by functionalizing a calix[4]arene scaffold with two dyes, was experimentally and theoretically characterized. The investigated compounds are highly versatile, due to the possibility of linking the dye molecules to the cone or partial cone structure of the calix[4]arene, which directs the two active units to the same or opposite side of the scaffold, respectively. The dynamics and efficiency of the EET process between the donor and acceptor units was investigated and discussed through a combined experimental and theoretical approach, involving ultrafast pump–probe spectroscopy and density functional theory based characterization of the energetic and spectroscopic properties of the system. Our results suggest that the external medium strongly determines the particular conformation adopted by the bichromophores, with a direct effect on the extent of excitonic coupling between the dyes and hence on the dynamics of the EET process itself.

Reliable computations of linear and non-linear optical properties of molecular systems in condensed phases require a proper account of stereo-electronic, vibrational, and environmental effects. In the framework of density functional theory, these effects can be accurately introduced using second-order vibrational perturbation theory in conjunction with polarizable continuum models. We illustrate the combination of an anharmonic description of the ground-state potential energy surface with solvation effects treated with the polarizable continuum model (PCM) in the calculation of the electronic, zero-point, and pure vibrational polarizabilities of selected systems. The description of the solvation environment is enriched by taking into account the dynamical aspects of the solute-solvent interactions through the inclusion of both electronic and vibrational non-equilbrium effects, as well as the direct effect of the solvent on the electric field that generates the molecular response (local field effect). This treatment yields accurate results which can be directly compared with experimental findings without the need of empirical corrections.