Molecular dynamics and simulations study on the vibrational and electronic solvatochromism of benzophenone

Abstract

Solvent plays a key role in diverse physico-chemical and biological processes. Therefore, understanding solute-solvent interactions at the molecular level of detail is of utmost importance. A comprehensive solvatochromic analysis of benzophenone (Bzp) was carried out in various solvents using Raman and electronic spectroscopy, in conjunction with Density Functional Theory (DFT) calculations of supramolecular solute-solvent clusters generated using classical Molecular Dynamics Simulations (c-MDSs). The >C=O stretching frequency undergoes a bathochromic shift with solvent polarity. Interestingly, in protic solvents this peak appears as a doublet: c-MDS and ad hoc explicit solvent ab initio calculations suggest that the lower and higher frequency peaks are associated with the hydrogen bonded and dangling carbonyl group of Bzp, respectively. Additionally, the dangling carbonyl in methanol (MeOH) solvent is 4 cm(-1) blue-shifted relative to acetonitrile solvent, despite their similar dipolarity/polarizability. This suggests that the cybotactic region of the dangling carbonyl group in MeOH is very different from its bulk solvent structure. Therefore, we propose that this blue-shift of the dangling carbonyl originates in the hydrophobic solvation shell around it resulting from extended hydrogen bonding network of the protic solvents. Furthermore, the 1(1)nπ(∗) (band I) and 1(1)ππ(∗) (band II) electronic transitions show a hypsochromic and bathochromic shift, respectively. In particular, these shifts in protic solvents are due to differences in their excited state-hydrogen bonding mechanisms. Additionally, a linear relationship is obtained for band I and the >C=O stretching frequency (cm(-1)), which suggests that the different excitation wavelengths in band I correspond to different solvation states. Therefore, we hypothesize that the variation in excitation wavelengths in band I could arise from different solvation states leading to varying solvation dynamics. This will have implications for ultrafast processes associated with electron-transfer, charge transfer, and also the photophysical aspects of excited states.

Intermolecular Hydrogen Bonding Controlled Intersystem Crossing Rates of Benzophenone

“…Solvent plays an active instead of a mere spectator role in various physicochemical and biological processes, − with the diverse solute–solvent interactions broadly classified as nonspecific or specific. − A recent study of the solvatochromic behavior of Bzp identified a linear correlation between the shifts in carbonyl stretching band vibrational frequencies observed by Raman spectroscopy and the UV band I (π* ← n) electronic transition frequencies with changing solvent polarity . In protic solvents, there are two distinct solvation states, with either a hydrogen-bonded (HBC) or a dangling carbonyl (DC) group of Bzp, and the observed correlation is consistent with selective excitation of Bzp molecules with a DC at the long-wavelength side of band I . In contrast, the shorter-wavelength regions of band I correspond predominantly to absorption by Bzp molecules with HBC groups, with a minor contribution from excitation to higher vibronic levels of the S 1 state of Bzp with a DC.…”

“…The S 1 /T 1 (nπ*) and the T 2 (ππ*) states of Bzp and similar aromatic ketones ,,, undergo hydrogen bond weakening and strengthening, respectively, compared to the ground state (S 0 ). Hydrogen bonding destabilizes the S 1 state, and photoexcitation of Bzp with a HBC to the S 1 state will induce reorganization along the HBC solvation coordinate.…”

The Effect of the Mixture Composition of BmimBF4-Acetonitrile on the Excited State Relaxation Dynamics of a Solar Cell Dye D149: An Ultrafast Transient Absorption Study

“…Thus, in order to get further insights regarding the interpretation of this timescale, we are planning to carry out molecular modeling to get information about the relaxation dynamics of D149 (relaxation time of twisting process of the dye, hydrogen bonding between dye and the components of IL-MS mixture). [66][67][68] In summary we can conclude that, for pure IL the origin of 3 is mainly due to solvation, whereas in case of pure ACN, the origin of 3 remains contradictory. Moreover, this relaxation time is affected by the decrease/increase of the polarity/viscosity of the D149 dye environment in a very similar fashion as 4 , i.e.…”

Physical Separation of H2 Activation from Hydrogenation Chemistry Reveals the Specific Role of Secondary Metal Catalysts

“…The rates at which C=O bonds were hydrogenated in ethanol, a polar protic solvent, were faster than those performed in non‐polar toluene (Supporting Information, Figure S6). It is reasonable to assume that protic polar solvents increase the hydrogenation rates of polar bonds ( δ+ C=O δ− ) through hydrogen bonding between the substrate and solvent [22, 32] . Polarity of organic solvent in the chemical compartment did not affect hydrogen flux: a similar amount of reactive hydrogen was delivered to the reaction surface regardless of the organic media used (Figure 4 a).…”

“…It is reasonable to assume that protic polar solvents increase the hydrogenation rates of polar bonds ( d+ C = O dÀ )t hrough hydrogen bonding between the substrate and solvent. [22,32] Polarity of organic solvent in the chemical compartment did not affect hydrogen flux:asimilar amount of reactive hydrogen was delivered to the reaction surface regardless of the organic media used (Figure 4a). Thef act that solvent does not affect Ha tom delivery stands in stark contrast to H 2 gas-fed hydrogenation, where the solvent governs H 2 solubility [16] and, in turn, the amount of hydrogen that can be delivered to the reaction surface (H 2 is generally more soluble in non-polar solvents than protic polar solvents).…”