TDDFT and MS‐CASPT2 Study of the Excited States of Para‐Methoxymethylcinnamate

Abstract

The vertical and adiabatic excitation energies of the ππ*, ππ*′, and nπ* states of the trans and cis isomers of para‐methoxymethylcinnamate (p‐MMC) were calculated using time‐dependent density functional theory and multistate complete active space second‐order perturbation theory (MS‐CASPT2) with reasonably sized basis sets. The adiabatic excitation energies of the ππ* state of trans‐p‐MMC calculated by TD‐CAM‐B3LYP and MS‐CASPT2 are in excellent agreement with the experimental value. The nπ* state lies at a higher energy than the ππ* state in the adiabatic excitation energy calculations, indicating that the barrier to internal conversion from the ππ* state to the nπ* state will be considerable. This result is opposite to the previous theoretical result. The microsolvation effect of a water molecule on p‐MMC is examined by calculating the excitation energies. The origin of the stabilization of the ππ* state and destabilization of the nπ* state by microsolvation has also been elucidated using natural population analysis.

193 nm Ultraviolet Photodissociation Mass Spectrometry of Tetrameric Protein Complexes Provides Insight into Quaternary and Secondary Protein Topology

“…There have been evidence and arguments for two general pathways: excitation to dissociative electronic states that results in fast dissociation directly from those states, and excitation followed by deactivation to ground electronic states from which the dissipated energy is sufficient to cleave the peptide backbone. 43–49 Both pathways may be operative in the present work. It is also interesting to note that the dichotomy between the fragmentation yield reflecting secondary structure and the observed charge state of the fragmenting monomers of SA, which were consistent with an asymmetric charge partitioning pathway, can be rationalized together in terms of a recent model proposed by Loo et al .…”

Elucidating the photoprotective properties of natural UV screening agents: ZEKE–PFI spectroscopy of methyl sinapate

“…Cinnamates and hydroxycinnamates 18,19,22,23,27,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] are from the above point of view a class of compounds of particular interest. They are ubiquitously employed in plants and bacteria for UV-B protection, while hydroxycinnamates are at the same time also used in nature as potent antioxidants.…”

A post-HF approach to the sunscreen octyl methoxycinnamate

“…27,31 In this context, a number of theoretical studies have investigated with a variety of techniques, including high-level quantum chemical approaches (complete active space selfconsistent field (CASSCF) and multi-state complete active space 2nd-order perturbation (MS-CASPT2)), the photophysical and photochemical properties of several cinnamate derivatives and/or reduced models of OMC -namely molecular structures including only the cinnamate chromophore nucleus but not the long aliphatic chain. [32][33][34][35][36][37][38][39][40][41][42][43] For example, the trans-cis photoisomerization route of substituted methylcinnamates was recently explored via single-component artificial force-induced reaction (SC-AFIR) combined with timedependent density functional theory (TD-DFT), highlighting a marked influence of the phenyl substituents on the decay mechanism. 42 Other studies at the TD-DFT/CIS level suggested appreciable solvent and hydrogen-bond effects on the photoisomerization mechanisms, 28,29 which were then corroborated by CASSCF and MS-CASPT2 calculations.…”