Evidence for Preferential Solvation in the Cyclohexane/n-Butanol Binary Solvent System

Interexcited State Photophysics I: Benchmarking Density Functionals for Computing Nonadiabatic Couplings and Internal Conversion Rate Constants

We present the first benchmarking study of nonadiabatic matrix coupling elements (NACMEs) calculated using different density functionals. Using the S₁ → S₀ transition in perylene solvated in toluene as a case study, we calculate the photophysical properties and corresponding rate constants for a variety of density functionals from each rung of Jacob's ladder. The singlet photoluminescence quantum yield (sPLQY) is taken as a measure of accuracy, measured experimentally here as 0.955. Important quantum chemical parameters such as geometries, absorption, emission, and adiabatic energies, NACMEs, Hessians, and transition dipole moments were calculated for each density functional basis set combination (data set) using density functional theory based multireference configuration interaction (DFT/MRCI) and compared to experiment where possible. We were able to derive simple relations between the TDDFT and DFT/MRCI photophysical properties; with semiempirical damping factors of ∼0.843 ± 0.017 and ∼0.954 ± 0.064 for TDDFT transition dipole moments and energies to DFT/MRCI level approximations, respectively. NACMEs were dominated by out-of-plane derivative components belonging to the center-most ring atoms with weaker contributions from perturbations along the transverse and longitudinal axes. Calculated theoretical spectra compared well to both experiment and literature, with fluorescence lifetimes between 7.1 and 12.5 ns, agreeing within a factor of 2 with experiment. Internal conversion (IC) rates were then calculated and were found to vary wildly between 10⁶-10¹⁶ s^-1 compared with an experimental rate of the order 10⁷ s^-1. Following further testing by mixing data sets, we found a strong dependence on the method used to obtain the Hessian. The 5 characterized data sets ranked in order of most promising are PBE0/def2-TZVP, ωB97XD/def2-TZVP, HCTH407/TZVP, PBE/TZVP, and PBE/def2-TZVP.

The Role of Hydrogen Bonding in the Preferential Solvation of 5-Aminoquinoline in Binary Solvent Mixtures

5-Aminoquinoline (5AQ) has been used as a fluorescent probe of preferential solvation (PS) in binary solvent mixtures in which the nonpolar component is diethyl ether and the polar component is protic (methanol) or aprotic (acetonitrile). Hence, the roles of solvent polarity and solute-solvent hydrogen bonding have been delineated. Positive deviations of spectral shifts from a linear dependence on the concentration of the polar component, signifying PS, are markedly more pronounced in case of the protic solvent. Solvation dynamics on a nanosecond time scale mark the formation of the solvation shell around the fluorescent probe. Time-resolved area-normalized emission spectra indicate the occurrence of the continuous solvation of the excited state when the polar component is acetonitrile. In contrast, two distinct states were observed when the polar component was methanol, the second state being the hydrogen bonded one. Translational diffusion is the rate-determining step for formation of the solvation shell. The time constant associated with it has been estimated from rise times observed in fluorescence transients monitored at the red end of the fluorescence spectra and also from the time evolution of the spectral width of time-resolved emission spectra.

Propyl acetate/butyronitrile mixture is ideally suited for investigating the effect of dielectric stabilization on (photo)chemical reactions

Characterization of propyl acetate/butyronitrile (PA/BuCN) mixtures by various spectroscopic techniques is described. The neat solvents have identical viscosities and refractive indices but their dielectric constants differ significantly. Detailed solvatochromic and titration data show that the mixtures do not exhibit specific solute-solvent interactions or significant dielectric enrichment effects. Therefore, the mixtures are ideally suited for investigating the effect of dielectric stabilization on (photo)chemical reactions. Dynamic Stokes shift experiments performed on two push-pull probes demonstrate that the solvation dynamics are significantly decelerated in the mixtures as compared to the neat solvents. Therefore, the mixtures allow for varying both the extent and time scale of the dielectric stabilization in a predictable manner.

Solvation properties of protic ionic liquid–molecular solvent mixtures

In this study, we have investigated the solvation properties of binary mixtures of PILs with molecular solvents. The selected binary solvent systems are the PILs ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) combined with either water, methanol, acetonitrile or DMSO.

Characterization of dimethylsulfoxide/glycerol mixtures: a binary solvent system for the study of “friction-dependent” chemical reactivity

The properties of binary mixtures of dimethylsulfoxide and glycerol, measured using several techniques, are reported.