Phosphorescent Modulation of Metallophilic Clusters and Recognition of Solvents through a Flexible Host-Guest Assembly: A Theoretical Investigation.

MP2 (Second order approximation of Møller⁻Plesset perturbation theory) and DFT/TD-DFT (Density functional theory/Time-dependent_density_functional_theory) investigations have been performed on metallophilic nanomaterials of host clusters [Au(NHC)2]⁺⋅⋅⋅[M(CN)2]-⋅⋅⋅[Au(NHC)2]⁺ (NHC = N-heterocyclic carbene, M = Au, Ag) with high phosphorescence. The phosphorescence quantum yield order of clusters in the experiments was evidenced by their order of µS1/ΔES1-T1 values ( µ S 1 : S0 → S1 transition dipole, ∆ E S 1 - T 1 : splitting energy between the lowest-lying singlet S1 and the triplet excited state T1 states). The systematic variation of the guest solvents (S1: CH3OH, S2: CH3CH2OH, S3: H2O) are employed not only to illuminate their effect on the metallophilic interaction and phosphorescence but also as the probes to investigate the recognized capacity of the hosts. The simulations revealed that the metallophilic interactions are mainly electrostatic and the guests can subtly modulate the geometries, especially metallophilic Au⋅⋅⋅M distances of the hosts through mutual hydrogen bond interactions. The phosphorescence spectra of hosts are predicted to be blue-shifted under polar solvent and the excitation from HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) was found to be responsible for the ³MLCT (triplet metal-to-ligand charge transfer) characters in the hosts and host-guest complexes. The results of investigation can be introduced as the clues for the design of promising blue-emitting phosphorescent and functional materials.

The mutual interactions based on amphipathic tetraoxacalix[2]arene[2]triazine: recognition cases of anion and cation investigated by a computational study.

The nature of anion···π (anion X1-4(-) = SCN(-), PF6(-), BF4(-) and NO3(-), respectively) interactions with electron-deficient and cavity self-tunable macrocyclic host tetraoxacalix[2]arene[2]triazine 1 as electron-acceptor (J. Am. Chem. Soc., 2013, 135, 892) have been theoretically investigated with the density functional theory (B3LYP, M06-2X, M06-L, M06, M05-2X, M05, DFT-D3) and the second-order Møller-Plesset perturbation theory (MP2) using a series of basis sets. The binding energies calculated are in good quantitative agreement with the experiments. The LMO-EDA (local molecular orbital energy decomposition analysis) results show that the major contributors of anion···π are electrostatic. The alkali metal cations M(+) (Na(+), K(+)) and alkaline earth metal cations M(2+) (Mg(2+), Ca(2+)) can also interact with 1 and, the cation···π binding of M(2+)···1 is stronger than that of M(+)···1, as well as their strength is gradually decreased along with an increase in the radius of M(+,2+). The investigation of interplay between the anion···π and the cation···π shows that the interactions among three-body, X(-), 1 and M(+) is varied with different phases. The polar solvent can strongly reduce the strength of the interaction, and the more increased the solvent polarity, the more reduced is the binding energy.

Theoretical study of the electronic-vibrational coupling in the Q(y) states of the photosynthetic reaction center in purple bacteria.

Inspired by the recent observation of correlated excitation energy fluctuations of neighboring chromophores (Lee et al. Science 2007, 316, 1462), quantum chemistry calculations and molecular dynamics simulations were employed to calculate the electronic-vibrational coupling in the excited states of the photosynthetic reaction center of purple bacteria Rhodobacter (Rb.) sphaeroides. The ground states and lowest excited (Q(y)) states of isolated bacteriochlorophyll a (BChl a) and bacteriopheophytin (BPhe) molecules were first optimized using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Normal mode analyses were then performed to calculate the Huang-Rhys factors of the intramolecular vibrational modes. To account for intermolecular electronic-vibrational coupling, molecular dynamics simulations were first performed. The ZINDO/S method and partial charge coupling method were then used to calculate the excitation energy fluctuations caused by the protein environment and obtain the spectral density. No obvious correlations in transition energy fluctuations between BChl a and BPhe pigments were observed in the time scale of our MD simulation. Finally, by comparing the calculated absorption spectra with experimental ones, magnitudes of inhomogeneous broadening due to the static disorder were estimated. The large amplitude of the static disorder indicates that a large portion of the spectral density and their correlations may still be hidden in the inhomogeneous broadening due to the finite MD simulation time.

Theoretical study on charge carrier mobilities of tetrathiafulvalene derivatives.

We calculated the hole and electron mobilities of tetrathiafulvalene (TTF) derivative crystals using first-principles calculations and the Marcus theory of electron transfer. The hole and electron reorganization energies were found to decrease with the extension of π-conjugated orbitals. The calculated hole mobilities of TTF, dibenzo-tetrathiafulvalene (DB-TTF), and dinaphtho-tetrathiafulvalene (DN-TTF) agree well with the experimental results. In addition, with the increase of the number of benzene rings attached to the TTF skeleton, the hole mobilities decrease and the electron mobilities increase. The calculated electron mobility of dianthro-tetrathiafulvalene (DA-TTF) based on a virtual crystal structure is much larger than the hole one due to the small electron reorganization energy and large electron coupling. This suggests that the charge transfer properties of the TTF derivatives can be modified when the number of aromatic rings on TTF skeleton increases.

Prediction and characterization of the single-electron sodium bond complexes Y-C...Na-H [Y = H3, H3CH2, (H3C)2H and (H3C)3].

The prediction and characterization of the single-electron sodium bond complexes Y-C...Na-H [Y = H(3), H(3)CH(2), (H(3)C)(2)H and (H(3)C)(3)] have been investigated for the first time by using MP2/6-311++G(d,p), MP2/6-311++G(2d,2p) and MP2/aug-cc-pVDZ methods. The strength of the interactions in H(3)C...Na-H, H(3)CH(2)C...Na-H, (H(3)C)(2)HC...Na-H, and (H(3)C)(3)C...Na-H complexes has been analyzed. It is shown that the (H(3)C)(3)C radical with Na-H forms the strongest single-electron sodium bond, followed by the (H(3)C)(2)HC radical and then the H(3)CH(2)C radical. H(3)C radical forms the weakest single-electron sodium bond. NBO and AIM analyses have also been used to estimate such conclusions. Furthermore, there are few linear/nonlinear relationships among the several parameters in system and the interaction mode of single-electron Na bond is LP(1)(C) --> LP(1)*(Na), which is different from the single-electron H bond and single electron halogen bond. By comparisons with some related systems, it is concluded that the strength of single-electron bond is increased in the order: hydrogen bond < sodium bond < bromine bond < lithium bond.