Insights into structural, solvent effect, molecular properties and NLO behavior of hemithioindigo-photoisomerization : A DFT study

Theoretical study by DFT and TD-DFT of NLO-active push-pull molecules composed of conjugated bridges based on cyclic rings: Titanol, Ferrol, Nickelol and Zinkol

CONTEXT

This research is based on the theoretical study of seven push-pull molecules composed of conjugated bridges based on two different organometallic rings, these bridges are linked at their ends by acceptor groups (-NO2) and donor groups (-N(CH3)2) on the α position of the rings mentioned above. The location of the donor and acceptor groups revealed that the addition of the acceptor groups near the rings (Titanol, Ferrol and Nickelol) improves the NLO response in comparison with the grafting of these groups on the Zinkol ring and also influences the positioning of the π electrons at the level of the chromophores studied. The molecule 2B gave the highest values ​​of static first hyperpolarisabilitiy (βtot) and static second hyperpolarisabilitiy (γav), knowing that: βtot (2B) = 135.79 * 10-30 esu and γav (2B) = 135.79 * 10-35 esu. The highest values ​​of dynamic firstβ ‖ λ - 2 ω ; ω , ω and secondγ ‖ λ - 2 ω ; ω , ω , 0 hyperpolarisabilities are assigned to the molecule 1C with the following values:γ ‖ λ - 2 ω ; ω , ω , 0 =1,218,310.00 * 10-30 esu andγ ‖ λ - 2 ω ; ω , ω , 0 =1,324,520,000 * 10-35 esu. The metal Zn is considered as an acceptor group and the remaining metals (Ti, Fe and Ni) are considered as donor groups. The specific solvents for the seven molecules are water, ethanol and acetonitrile. The maximum wavelengths recorded for all molecules in combination with all solvents are in the range of 421.39 to 765.28 nm. λ METHOD: The calculations were performed using Gaussian 16 software to perform DFT calculations with B3LYP functional. The LanL2DZ basis-set was used for transition metals, while the 6-31 +  + G(d,p) basis-set was used for nonmetal atoms. The functionals used are: CAM-B3LYP, LC-wPBE, LC-BLYP, M11, wB97X, M08-HX, M06-2X, MN12SX, MN15, and M06HF. The basis-sets used are: 6-31G(d,p), 6-31 +  + G(d,p), cc-pVDZ, aug-cc-pVDZ, 6-311G(d,p), 6-311 +  + G(d,p), cc-pVTZ, and aug-cc-pVTZ. The Natural Bond Orbital (NBO) calculations are performed by the NBO program incorporated by default in the Gaussian 16 program. The solvation models studied are the CPCM model (conductor polarizable continuum model) and the SMD model (Solvation Model Density). Excited states calculations are calculated by the time-dependent DFT method (TD-DFT).

"On-the-Fly" Nonadiabatic Dynamics Simulation on the Ultrafast Photoisomerization of a Molecular Photoswitch Iminothioindoxyl: An RMS-CASPT2 Investigation

Iminothioindoxyl (ITI) is a new class of photoswitch that exhibits many excellent properties including well-separated absorption bands in the visible region for both conformers, ultrafast Z to E photoisomerization as well as the millisecond reisomerization at room temperature for the E isomer, and switchable ability in both solids and various solvents. However, the underlying ultrafast photoisomerization mechanism at the atomic level remains unclear. In this work, we have employed a combination of high-level RMS-CASPT2-based static electronic structure calculations and nonadiabatic dynamics simulations to investigate the ultrafast photoisomerization dynamics of ITI. Based on the minimum-energy structures, minimum-energy conical intersections, linear interpolation internal coordinate paths, and nonadiabatic dynamics simulations, the overall photoisomerization scenario of ITI upon excitation is established. Upon excitation around 416 nm, the molecule will be excited to the S2 state considering its close energy to the experimentally measured absorption maximum and larger oscillator strength, from which ultrafast decay of S2 to S1 state can take place efficiently with a time constant of 62 fs. However, the photoisomerization is not likely to complete in the S2 state since the dihedral associated with the Z to E isomerization changes little during the relaxation. Upon relaxing to the S1 state, the molecule will decay to the S0 state ultrafast with a time constant of 232 fs. In contrast, the decay of the S1 state is important for the isomerization considering that the dihedral related to the isomerization of the hopping structures is close to 90°. Therefore, the S1/S0 intersection region should be important for the isomerization of ITI. Arriving at the S0 state, the molecule can either go back to the original Z reactant or isomerize to the E products. At the end of the 500 fs simulation time, the E configuration accounts for nearly 37% of the final structures. Moreover, the photoisomerization mechanism is different from the isomerization mechanism in the ground state; i.e., instead of the inversion mechanism in the ground state, the photoisomerization prefers the rotation mechanism. Our results not only agree well with previous experimental studies but also provide some novel insights that could be helpful for future improvements in the performance of the ITI photoswitches.

Theoretical study of the Tetraaminelithium and Tetraaminesodium molecules complexed with H-, Li- and Na- anions: static and dynamic NLO parameters

CONTEXT

This work focuses on the study of six molecules composed of the TetraAmineLithium (TALi+) and TetraAmineSodium (TANa+) structures linked with the anions H-, Li- and Na-. The NLO results obtained by these calculations showed significant values of static first hyperpolarizabilities (βtot) ranging from 8.74 * 10-30 to 691.99 * 10-30 esu. The two molecules TALi-Li and TALi-Na gave the highest values of static βtot equal to 563.20 and 691.99 * 10-30 esu respectively and static second hyperpolarizabilities (γav) of 680.02 and 779.05 * 10-35 esu. The highest dynamic first hyperpolarizabilities (β||) values are around 1474080.00 * 10-30 esu and 6,145,080.00 * 10-30 esu at 720 nm lasers and which are attributed to the two molecules TANa-Li and TANa-Na respectively. Four molecules have push-pull behavior where the anions are donor groups, the Li+-NH3 and Na+-NH3 groups are acceptor groups and a bridge composed by the three remaining NH3 ligands. The maximum wavelengths (λmax) in vacuum and in the presence of solvents for all molecules are in the range 240 to 870 nm.

METHOD

The software used in this study is Gaussian 16. The optimizations of the molecules were calculated by B3LYP-D3/6-31 +  + G(d,p). The static first hyperpolarizability (βtot) was calculated by different functionals: CAM-B3LYP, LC-wPBE, LC-BLYP, M11, wB97X, HSEh1PBE and M06-2X and the MP2 method, the basis-set used is 6-31 +  + G(d,p). Other calculations of static βtot were carried out by the CAM-B3LYP functional combined with several basis-sets: 6-31G(d,p), 6-31 +  + G(d,p), cc-pVDZ, AUG-cc- pVDZ, 6-311G(d,p), 6-311 +  + G(d,p), cc-pVTZ and AUG-cc-pVTZ. The calculations of the first (β||) and second (γ||) hyperpolarizabilities in second harmonic generation (SHG) were calculated by CAM-B3LYP/6-31 +  + G(d,p). The delocalization energies (E(2)) were determined by the NBO approach and calculated by the same functional and basis-set cited before. The solvation Gibbs energies (ΔGsolv) were calculated using the implicit SMD model. Maximum wavelengths (λmax) and oscillator strengths ([Formula: see text]) were calculated by TD-CAM-B3LYP/6-31 +  + G(d,p) in the presence of the implicit CPCM model.