Serra Arslancan

Carotenoids are natural pigments with multiple roles in photosynthesis. They act as accessory pigments by absorbing light where chlorophyll absorption is low, and they quench the excitation energy of neighboring chlorophylls under high-light conditions. The function of carotenoids depends on their polyene-like structure, which controls their excited-state properties. After light absorption to their bright S₂ state, carotenoids rapidly decay to the optically dark S₁ state. However, ultrafast spectroscopy experiments have shown the signatures of another dark state, termed S_X. Here we shed light on the ultrafast photophysics of lutein, a xanthophyll carotenoid, by explicitly simulating its nonadiabatic excited-state dynamics in solution. Our simulations confirm the involvement of S_X in the relaxation toward S₁ and reveal that it is formed through a change in the nature of the S₂ state driven by the decrease in the bond length alternation coordinate of the carotenoid conjugated chain.

The association of Cu–X (X = –H, –Cl, and –F) with H₂CCHCH_mY_n and HCCCH_mY_n (Y = –Cl, –F, –OH, –CH3) has been studied at a high level of theory. The density functional theory (DFT) at B3LYP/6-311G(d,p)//B3LYP/6-311 + G(3df,2p) level has been chosen to calculate the structure and the relative stability of 24 different complexes. The interaction of Cu–F with the derivatives of ethylene and acetylene was found very strong, with interaction energies close to those of conventional covalent bonds. In all complexes, the most stable structure was found when Cu–X is positioned on the unsaturated CC bond, forming a three-membered ring that leads to longer CC bond distances. Both ethylene and acetylene complexes show similar trends of interaction energies with respect to the same moiety. All electronic indexes analyzed by means of the QTAIM, ELF, and NBO formalisms indicate that the strength of the interaction should increase with the number of withdrawing substituents in both series of compounds. The p-Interaction of ethylene and acetylene derivative with fluoride copper. The ELF graphs and its 2D projection show the disynaptic basins of the electrostatic binding

Molding purine PES through functionalization: whilst purine C₂-substitution maintains the features of the spectroscopic PES of the heterocycle, C₆-functionalization reshapes its topography leading to photostable systems.

B3LYP/6‐311+G(3df,2p)//B3LYP/6‐31+G(d,p) density functional theory calculations show that cyclopentene and cyclopentyne derivatives yield very strong π‐type complexes with HCu and FCu molecules. This interaction is so strong in the case of cyclopentyne derivatives that the complexes formed can be considered as a new kind of metallocycles. These complexes resemble those reported before in the literature for ethylene and acetylene, though whereas the interaction energies between cyclopentene and HCu and FCu are smaller than those reported for ethylene, those involving cyclopentyne are larger than the ones calculated for acetylene. This very different behavior is due to the dramatic change in the local environment of the two carbon atoms of cyclopentyne with respect to acetylene, which does not occur on going from ethylene to cyclopentene. The introduction of heteroatoms in the five‐membered rings opens the possibility of forming other isomers in which the CuX (X = H, F) is attached to the heteroatom rather than to the unsaturated CC bond. This arrangement is precisely the most favorable one for cyclopentene derivatives, though for cyclopentyne ones the π‐type complexes are still the global minima.

Interest in understanding the photophysics and photochemistry of thiated nucleobases has been awakened because of their possible involvement in primordial RNA or their potential use as photosensitizers in medicinal chemistry. The interpretation of the photodynamics of these systems, conditioned by their intricate potential energy surfaces, requires the powerful interplay between experimental measurements and state of the art molecular simulations. In this review, we provide an overview on the photophysics of natural nucleobases’ thioanalogs, which covers the last 30 years and both experimental and computational contributions. For all the canonical nucleobase’s thioanalogs, we have compiled the main steady state absorption and emission features and their interpretation in terms of theoretical calculations. Then, we revise the main topographical features, including stationary points and interstate crossings, of their potential energy surfaces based on quantum mechanical calculations and we conclude, by combining the outcome of different spectroscopic techniques and molecular dynamics simulations, with the mechanism by which these nucleobase analogs populate their triplet excited states, which are at the origin of their photosensitizing properties.