Exploiting the role of coadsorbents on photovoltaic performances of dye sensitized solar cells: A DFT study.

We examine the role of coadsorbents on dye-sensitized solar cells (DSSCs) with metal-containing and metal-free organic dyes to assess the performance computationally. The results corroborate well with the reported experimental results of Ru-containing dyes exhibiting that the co-adsorbent with longer alkyl chains anchored on the semiconductor surface lower the electron recombination process. The calculated results reveal that the co-adsorbents influence the conduction band energy level and that improve the effective density of states augmenting the forward electron transmission as well as reducing the electron recombination process. The role of co-adsorbents with metal-free organic dyes in DSSCs has also been examined. The computational results suggest that the metal-free organic dyes employed in DSSCs can achieve similar efficiency as reported with metal-organic sensitizers. The results revealed that co-adsorbents grafted through non-covalent interaction are more efficient in improving the efficiency of the DSSCs than co-adsorbents grafted through covalent bonds. The coadsorbents, 1-dimethoxyphosphoryloctadecane with long alkyl chains anchored on the semiconductor surface through hydrogen bonding interactions highly improve the effective density of states resulting in better forward electron transmission and may be one of the parameters to enhance the DSSCs efficiency.

Exploiting the (-C-H···C-) Interaction to Design Cage-Functionalized Organic Superbases and Hyperbases: A Computational Study.

A set of carbon center-based P-ylidesubstituting bases have been exploited computationally with pentacyclo[5.4.0.02,6.03,10.05.9]undecane (PCU) and pentacyclo [6.4.0.02,7.03,11.06,10] dodecane (PCD) scaffolds using the B3LYP-D3/6-311+G(d,p) level of theory. The proton affinities calculated in the gas phase are in the range of superbases and hyperbases. The Atomsin-Molecules and Natural Bond Orbital calculations reveal that the -C-H···C- interaction plays a substantial role in improving the basicity, and tuning the -C-H···C- interaction can enhance the basicity of such systems. The free activation energy for proton exchange for PCD and PCU scaffolds substituted with P-ylide is substantially low. The computed results reveal the strength and nature of such - C-H···C- interactions compared to the -N-H···N- hydrogen bonds. The isodesmic reactions suggest that the superbasicity achieved using these frameworks arises from a combination of several factors, such as the ring strain of the bases in their unprotonated form, steric repulsion, and the intramolecular -C-H···C- interaction.

Cooperativity between the Substrate and Ligand in Palladium-Catalyzed Allylic Alkylation Using 1-Aryl-1-propynes.

A monoprotected amino acid Bz-Gly-OH assists in the allylic alkylation of a variety of ketones, ß-keto esters, aldehydes, etc., during enamine-palladium catalysis. Density functional theory calculations reveal that Bz-Gly-OH assists in the formation of an enamine that attacks the π-allylpalladium complex via an outer sphere mechanism. The preliminary result points to an asymmetric allylic alkylation under a new mode of bifunctional catalysis.

DFT exploration to tune the silyl group as anchoring unit on the performance of dye-sensitized solar cells: an approach to suppress dye leaching from semiconductor surface.

In this work, we report the lower stability of dyes containing cyanoacrylic acid anchoring group on semiconductor TiO2 surface compared to the corresponding silyl unit in dye-sensitized solar cell. Density functional theory (DFT) calculations have been performed with simple donor (N,N diphenylamine) and π-conjugated spacers, with silyl anchoring groups to examine the efficiency of DSSCs. The calculated results in CAM-B3LYP/6-31G(d)/CPCM(THF) reveal that the cyanoacrylic acid anchoring group would have weaker coordination on semiconductor TiO2 surface compared to the silyl anchoring group on the same surface. The designed dyes 1-7 exhibit comparable or in cases superior optical properties than that of the reference dye molecule with cyanoacrylic acid as an anchoring group. All designed dyes have lower ΔGrejection values implying efficient and faster electron recombination between the dye and electrolyte. The electron transition coefficient for these dyes is higher enough (~72-87%) suggesting successful electron propagation from dye to the semiconductor. The electron-donating methyl and ethyl groups show lower ΔGrejection values than the commonly studied -OEt substitution with the silyl anchoring group. The extended π conjugation for better electronic propagation and higher λmax values have been achieved with simple ethylene and butadiene units in the dye molecules. Dye 7 with butadiene as π-spacer unit shows superior oscillatory strength (f) of 2.19 and light-harvesting efficiency (LHE) of 0.99 than the other studied dyes and reference dye with carboxylic anchoring group (TA-ST-CA). The lowest ΔGrejection value (0.53 eV) of dye 7 suggests better electronic recombination than all the other dyes studied here. Transition Density matrix and PDOS calculations with the representative dye 7 suggest a good electronic propagation from the dye to the semiconductor. The incorporation of a highly π-conjugated spacer 4,8-di(thiophen-2-yl)-1H,5H-benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole) in dye 7 (7-BBT) showed remarkable enhancement in the absorption maxima ~800 nm corresponds to the UV-vis and NIR regions. The DFT calculated results shed light on designing new DSSCs with silyl anchoring groups for enhanced stability and superior efficiency.

Exploiting σ-hole interaction to design small uncharged ligand molecules to stabilize G-quadruplex-DNA: a computational study.

Small neutral seleno molecules were designed to stabilize G-quadruplex-DNA to accelerate the death of cancer cells. A new approach was considered in this study to design new ligands to stabilize G-quadruplex-DNA using the non-covalent σ-hole interaction. The systematic study has been performed with ligands in the absence and presence of σ-hole interaction to stabilize G-tetrad. Fluorine-substituted seleno ligands interact with the bases of G-quadruplex strongly with the σ-holes present in the ligands. The binding of the fluorinated ligands FSeCF2SeCF2 SeF2(4) (~75.0 kcal/mol) is stronger than that of BRACO-19 (~70.0 kcal/mol) calculated at the same level of theory with G-tetrad. It is reported that BRACO-19 is employed to inhibit the enzymatic activity of telomerase. The calculated results also reveal the importance of optimum chain length of ligands to achieve a better binding ability with G-tetrad. The MESP calculations and AIM analysis corroborate the trends of binding of these ligand molecules with G-quadruplexes. The small neutral molecules possess considerable advantage to pass through the lipid bilayer of the cell membrane by passive transport and are of choice in biological research and for clinical trials. Graphical AbtractSmall neutral ligands with σ-holes can stabilize G-quadruplex to inhibit enzymatic activity of telomerase.

A DFT study to probe homo-conjugated norbornylogous bridged spacers in dye-sensitized solar cells: an approach to suppressing agglomeration of dye molecules.

This work reports a sigma-bridged framework as spacers to design new dye-sensitized solar cells. The norbornylogous bridged spacer can avoid π-π aggregation of dye molecules on the semiconductor surface in DSSCs. These sesquinorbornatrienes are known to exhibit electron propagation through the interaction of sigma and π orbitals via through bond (OITB) and through space (OITS) mechanisms. Density functional theory (DFT) calculations performed with these spacers and a modelled simple donor unit like N,N-dimethylamine and cyanoacrylic acid as the anchoring group showed significant results with the requisite optical parameters for DSSCs. The newly designed dyes have shown comparable or better optical properties compared to the reference dye molecule with π-conjugated thiophene spacer units. The ΔG injection, V OC and µ normal values calculated for the designed dyes were found to be higher than those of the reference system. The trans-sesquinorbornatriene system spacer (6-D) showed a V OC of 3.3 eV, ΔG injection of 2.4 eV and oscillatory strength (f) of 0.96. The total and partial density of states indicates a good communication between the valence and conduction band for the designed dyes. Transition density matrix results suggest that the exciton dissociation in the excited state is sufficiently high to overcome the coulombic attraction of the hole. These results are promising for the design of dye molecules with such scaffolds, to achieve better efficiency and to eliminate one of the major issues with π-spacer units in DSSCs.

A new strategy to generate super and hyper acids with simple organic molecules exploiting σ-hole interaction.

Super and hyper acidity can be achieved using σ-hole non-covalent interactions with simple organic systems. The σ-hole interaction can stabilize the conjugate base of acids to such an extent that cyclopentadiene yields a ΔHacid of 256 kcal mol-1, which is ∼100 kcal mol-1 lower than the reported results. The hyper acidic value of 209.0 kcal mol-1 of organic acids has been achieved without electron-withdrawing substituents rather exploiting only σ-hole interaction. Remarkably, the 1st and 2nd acidity values (∼229 kcal mol-1) of comparable strength in the hyperacid range have been observed for the first time using DFT computations. The simple organic acids were predicted to reach the pKa values in the range of -7.3 to -7.8 in DMSO, which is remarkably lower than previous reports. These stable anions can be a potential candidate for application as an effective electrolyte in lithium-ion batteries.