Ahmad Irfan

Quantum chemical study of the donor-bridge-acceptor triphenylamine based sensitizers.

Quantum chemical calculations were carried to investigate the electron coupling, electron injection, electronic and photophysical properties of 2-cyano-5-(4-(phenyl(4-vinylphenyl)amino)phenyl) penta-2,4-dienoic acid (TC4) and its derivatives. Geometries have been optimized by using density functional theory at B3LYP/6-31G(**) level of theory. The highest occupied molecular orbitals (HOMOs) are delocalized on triphenylamine (TPA) units while lowest unoccupied molecular orbitals LUMOs are localized on anchoring groups. The mono-methyl is more significant to lowering the energy gap than di and tri-methyl substituted ones. The HOMOs of the dyes are below the redox couple and LUMOs are above the conduction band of TiO2. We have explained the recombination barrier on the basis of distortion and coplanarity. The excitation energies have been computed by time dependent density functional theory at PCM-CAM-B3LYP/6-31G(**) level of theory. Enhanced bridge is encouraging to promote the electron injection, electronic coupling constant and light harvesting efficiency. Generally, electron injection, electronic coupling constant and light harvesting efficiency of new designed sensitizers are higher than TC4. This revealed that new materials would be efficient photosensitizers.

Quantum chemical design of nonlinear optical materials by sp2-hybridized carbon nanomaterials: issues and opportunities

Nonlinear optical (NLO) materials are the smartest materials of the era, and have the ability to generate new electromagnetic fields with changed frequencies, phases, and other physical properties. Recently, many cutting edge research reports have been focused on NLO materials especially on those which are composed of sp2 hybridized carbon nanostructures. As the carbon nanostructures are composed of abundant π-electrons and have significant delocalization, these are potential candidates for modern NLO materials. Generally, sp2 hybridized carbon nanostructures can be divided into zero-dimensional fullerenes, one-dimensional nanotubes and two-dimensional graphene nanoribbons and quantum dots etc. These dimensionally different carbon nanomaterials are promising candidates for a wide range of applications in next-generation nanotechnologies. In present feature article, we first briefly explain a theoretical structure–NLO property relationship based on perturbation theory and then elucidate the crucial factors to control the NLO responses. We put together the different random investigations of sp2 hybridized carbon nanostructures for NLO application by highlighting the importance of their several structural designs to tune NLO amplitudes. Furthermore, we make a comparative and updated analysis of the NLO properties of dimensionally different sp2 hybridized carbon nanomaterials i.e. fullerenes, carbon nanotubes, and graphene nanoribbons and quantum dots. Finally, we make a brief discussion about different aspects and opportunities to use the sp2 hybridized carbon nanomaterials as high performance NLO materials of the future. This review is a focused perspective based on different updated quantum chemical investigations about fullerenes, nanotubes and graphene nanoribbons and quantum dots for their possible use in nonlinear optical applications.

The DFT investigations of the electron injection in hydrazone-based sensitizers

Quantum chemical calculations were carried out by using density functional theory and time-dependant density functional theory at B3LYP/6-31G(d) and TD-B3LYP/6-31G(d) level of theories. The absorption spectra have been computed with and without solvent. The calculated absorption spectra in ethanol, acetonitrile, and methanol are in good agreement with experimental evidences. The absorption spectra are red shifted compared to System1. On the basis of electron injection and electronic coupling constant, we have shed light on the nature of different sensitizers. The coplanarity between the benzene near anchoring group having LUMO and the bridge (N–N) is broken in System6 and System7 that would hamper the recombination process. The electron injection of System2–System10 is superior to System1. The highest electronic coupling constant has been observed for System6 that followed the System7 and System8. The light-harvesting efficiency of all the sensitizers enlarged in acetonitrile and ethanol. The long-range-corrected functional (LC-BLYP), Coulomb-attenuating method (CAM-B3LYP), and BH and HLYP functional underestimate the excitation energies while B3LYP is good to reproduce the experimental data. Moreover, we have investigated the effect of cyanoacetic acid as anchoring group on the electron injection.

An investigation on the key features of a D–π–A type novel chalcone derivative for opto-electronic applications

The current study is focused on the donor–bridge–acceptor (D–π–A) type of novel organic charge transport and non-linear optical material, 1-(4-bromophenyl)-3-(2,4,5-trimethoxyphenyl) prop-2-en-1-one (2,4,5-TMBC) to spotlight its various important properties through experimental and quantum chemical approaches. The compound 2,4,5-TMBC was synthesized via a Claisen–Schmidt condensation reaction and its single crystal was grown by a slow evaporation solution growth technique. FT-IR and FT-Raman spectra of 2,4,5-TMBC were obtained and investigated. The molecular geometry of 2,4,5-TMBC was optimized by HF, B3LYP, CAM-B3LYP, wb97xd and LC-BLYP methods using the 6-31G* basis set. The calculated geometrical parameters and vibrational spectra are in good agreement with the experimental results. Time dependent density functional theory (TD-DFT) has been applied to investigate the optical properties of the title compound. The absorption wavelength calculated at the TD-B3LYP/6-31G* level of theory in the gas phase was in good agreement with the experimental value (∼400 nm) when compared with other methods. The HOMO–LUMO energy gap was calculated at all the applied levels of theory. The total dipole moment, polarizability, anisotropy of polarizability and static first and total hyperpolarizability values of 2,4,5-TMBC were calculated at different levels of theory. The dipole moment and first hyperpolarizability values are found to be many folds (2 and 56 times calculated at B3LYP) higher than urea. It is also expected that 2,4,5-TMBC would be electron transport material due to its smaller electron reorganization energy value. The study of non-linear optical (NLO) properties shows that 2,4,5-TMBC would be an outstanding candidate for NLO device applications.

A dual approach to study the electro-optical properties of a noncentrosymmetric L-asparagine monohydrate.

In this work we reports the experimental and theoretical investigation on an organic noncentrosymmetric monohydrated L-asparagine (LAM) molecule. LAM single crystals were grown in specially designed beaker for the first time. Structural confirmation was done by identifying the vibrational modes using IR and FT-Raman spectroscopic studies. The ultra violet-visible-near infrared absorbance, diffuse reflectance spectra were recorded in the spectral range 190-2500 nm. The optical transparency was calculated and found to be ∼80%. Its optical band gap was calculated found to be ∼5.100 eV. Density functional theory (DFT) was employed to optimize the molecular geometry of LAM using B3LYP/6-31G(∗) basis set of theory. The HOMO-LUMO energy gap of 6.047 eV and transition energy of 176 nm (f0=0.024) have been found in semi-quantitative agreement with our experimental results. The dipole moment, polarizability and first hyperpolarizability were calculated at the same level of theory. The obtained results reveals that the titled compound can be a decent contender for nonlinear applications.

Quantum chemical investigations aimed at modeling highly efficient zinc porphyrin dye sensitized solar cells

AbstractZinc tetraphenylporphyrin (ZnTPP) was modified by a push-pull strategy and then density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed for the resulting derivatives. The smallest HOMO–LUMO energy gaps were found in ZnTPP-6 and ZnTPP-7, which had nitro substituents and a conjugated chain, while the largest was observed for ZnTPP-5. The energy gaps of all of the systems designed in this work were smaller than that of ZnTPP. Clear intramolecular charge transfer was observed from donor to acceptor in ZnTPP-6 and ZnTPP-7, which had nitro groups at positions R8, R9, and R10, as well as in ZnTPP-3 and ZnTPP-4, which had cyano groups at those positions. The narrow band gaps (compared to that of ZnTPP) of these designed systems, where the LUMO is above the conduction band of TiO2 and the HOMO is below the redox couple, indicate that they are efficient sensitizers. The B bands of these newly designed derivatives, except for ZnTPP-5, are redshifted compared with the B band of ZnTPP. FigureThe comprehensive intra charge transfer has been observed from highest occupied molecular orbitals to lowest unoccupied molecular orbitals. The LUMO of the designed systems lying above the conduction band of TiO2 and HOMO below the redox couple as well as the narrow band gap compared to ZnTPP showed that new designed materials would be efficient sensitizers.

Packing Effect on the Transfer Integrals and Mobility in α,α′-bis(dithieno[3,2-b:2′,3′-d]thiophene) (BDT) and its Heteroatom-Substituted Analogues

Theoretically calculated mobility has revealed that BDT is a hole transfer material, which is in good agreement with experimental investigations. The BDT, NHBDT, and OBDT are predicted to be hole transfer materials in the C2/c space group. Comparatively, hole mobility of BHBDT is 7 times while electron mobility is 20 times higher than the BDT. The packing effect for BDT and designed crystals was investigated by various space groups. Generally, mobility increases in BDT and its analogues by changing the packing from space group C2/c to space groups P1 or . In the designed ambipolar material, BHBDT hole mobility has been predicted 0.774 and 3.460 cm2 Vs–1 in space groups P1 and , which is 10 times and 48 times higher than BDT (0.075 and 0.072 cm2 Vs–1 in space groups P1 and ), respectively. Moreover, the BDT behaves as an electron transfer material by changing the packing from the C2/c space group to P1 and .

Synthesis, characterization and DFT study of methoxybenzylidene containing chromophores for DSSC materials.

Novel tricyanovinyl derived from hydrazones have been prepared by the reaction of tetracyanoethylene and phenylethylidene hydrazone, and these dyes showed absorption in the region of 539-650 nm. The dyes showed pronounced solvatochromic effects as the polarity of the solvents changed. The torsion in E isomer is smaller than Z and azo isomers of MBD1 and MBD2. The HOMOs are delocalized on whole of the molecule while LUMOs are distributed on the tricarbonitrile. The LUMO energies are above the conduction band of TiO(2) and HOMOs of the dyes are below the redox couple of MBD1 and MBD2. The HOMO energies, LUMO energies and HOMO-LUMO energy gap of MBD1 and MBD2 are almost same. The absorption spectra of both the dyes in different solvents are approximately same except in cyclohexane.

Modeling of multifunctional donor-bridge-acceptor 4,6-di(thiophen-2-yl)pyrimidine derivatives: A first principles study

We have modeled multifunctional compounds by pi-elongation and push-pull strategy from the 4,6-di(thiophen-2-yl)pyrimidine. The ground state geometries have been optimized by density functional theory while excited state geometries were optimized by time dependent density functional theory (TDDFT). Structure-property relationship, electronic, optical and charge transfer properties (ionization potential, electron affinity and reorganization energies) were computed and discussed. By TDDFT absorption and emission have been calculated. The computed parameters were compared with available experimental data. The long-range corrected functional (LC-BLYP) is overestimating the highest occupied and lowest unoccupied molecular orbital energies, energy gaps while underestimating the absorption and fluorescence wavelengths. The B3LYP is good to reproduce the experimental data. The intra-molecular charge transfer has been observed from highest occupied molecular orbitals to lowest unoccupied molecular orbitals. The strong electron withdrawing and electron donor groups efficiently reduce the energy gaps. The decrease injection barrier and smaller reorganization energies are revealing that our designed derivatives would be efficient hole as well as electron transfer materials. These derivatives would be good light emitters e.g. blue, green, orange, red and near IR. The predicted values showed that the designed derivatives would be efficient for the organic field effect transistors, photovoltaics and light emitters.

Electronic, optical, and charge transfer properties of donor–bridge–acceptor hydrazone sensitizers

The ground state geometries have been computed by using density functional theory (DFT) at B3LYP/6-31G*, B3LYP/6-31G**, and PCM-B3LYP/6-31G* level of theories. The highest occupied molecular orbitals (HOMOs) are delocalized on whole of the molecule and the lowest unoccupied molecular orbitals (LUMOs) are localized on the tricarbonitrile. The lowest HOMO and LUMO energies have been observed for Dye1 while highest for Dye4. The LUMO energies of Dye1–Dye4 are above the conduction band of TiO2 and HOMOs are below the redox couple. The absorption spectra have been computed in solvent (methanol) and without solvent by using time-dependant DFT at TD-B3LYP/6-31G*, TD-B3LYP/6-31G**, and PCM-TD-B3LYP/6-31G* level of theories. The calculated maximum absorption wavelengths of the spectra in methanol are in good agreement with experimental evidences. The maximum absorption wavelengths of new designed sensitizers are red shifted compared to parent molecule. The electronic coupling constant and electron injection have been computed by first principle investigations. The improved electronic coupling constant and electron injection revealed that new modeled systems would be efficient sensitizers.