Manash Protim Borpuzari

Experimental and theoretical study of urea and thiourea based new colorimetric chemosensor for fluoride and acetate ions.

Two new anion receptors 1,1-(4-nitro-1,2-phenylene) bis(3-phenylurea) (1) and 1,1-(4-nitro-1,2-phenylene) bis(3-phenylthiourea) (2) have been reported here. The binding and colorimetric sensing properties of receptors 1 and 2 with different anions were investigated by naked-eye, (1)H-NMR and UV-Vis spectroscopy. They showed effective and selective binding with two biologically important anions F(-) and CH3COO(-), in presence of other anions, such as Cl(-), Br(-), I(-), NO2(-), ClO4(-), HSO4(-), H2PO4(-), N3(-), CN(-) in acetonitrile. The relative binding mode of fluoride and acetate anions towards receptors 1 and 2 were studied using density functional theory (DFT), in gas phase and in acetonitrile solvent. Computational studies revealed that receptor 1 formed complexes by two intermolecular hydrogen bonds while receptor 2 by three intermolecular hydrogen bonds. In addition, time dependent DFT (TD-DFT) calculations qualitatively match the experimental UV-Vis spectra.

Structural, electronic and reactivity studies on group 15 analogues of N-heterocyclic carbene

The present article reports density functional studies on the Group 15 analogues of N-heterocyclic carbene (NHC) on their structure, reactivity, stability and ligating properties. Long-range corrected density functionals have been used due to its recent success in predicting orbital energies. These ligands are found to have greater π-accepting ability than NHC. Electron-donating substituents have a dramatic effect on their stability as well as ligating properties. Furthermore, natural resonance theory (NRT) calculations have been performed to determine the percentage weighting of resonance contributing structures. In addition, density-based global reactivity descriptors such as chemical potential, hardness, electrophilicity index and softness are calculated using four different density functional methods, and compared with CCSD(T) results. Moreover, the density-based local reactivity descriptors are employed to study the reactivity of Group 15 analogues. From the plot of dual descriptors, it is found that the “ene” centre of the Group 15 analogues of NHC is pseudodual.

Assessment of range-separated functionals in the presence of implicit solvent: Computation of oxidation energy, reduction energy, and orbital energy

Recently, we have investigated the ionization potential (IP) theorem for some small molecules in the presence of external electric field [M. P. Borpuzari et al., J. Chem. Phys. 144, 164113 (2016)]. In this article, we assess the performance of some density functionals, local density approximation, generalized-gradient approximation (GGA), hybrid, meta-GGA hybrid, and range-separated functionals in the presence of two different solvent dielectrics, water and cyclohexane, in reproducing the vertical oxidation energy, reduction energy, and the frontier orbital energies. We also study the accessibility of different computational solvent models like the polarizable continuum model (PCM) and non-equilibrium PCM (NEPCM) in reproducing the desired properties. In general, the range-separated functionals do not perform well in reproducing orbital energies in the PCM. Range separation with the NEPCM is better. It is found that CAM-B3LYP, M06-2X, and ωB97XD functionals reproduce highest occupied molecular orbital energy in solvents, which may be due to the cancellation of PCM and density functional theory errors. Finally, we have tested the validity of the IP theorem in the solvent environment.

Antioxidant properties can be tuned in the presence of an external electric field: accurate computation of O–H BDE with range-separated density functionals

In this article, we have studied the effect of the external electric field on the antioxidant properties of gallic and caffeic acids. The variation of the O–H bond dissociation enthalpy (BDE), adiabatic ionization energy, proton dissociation enthalpy, proton affinity and electron transfer enthalpy, in the presence of an external electric field is studied. It is found that the antioxidant properties can be tuned by the application of an external electric field. In addition, the O–H bond strength, qualitatively measured from the O–H bond length, is found to depend on the external electric field. Furthermore, the performance of seven range-separated density functionals in the presence of the external electric field is reported for the first time. On comparing with the composite model CBS-QB3, it is found that the LC-BLYP functional reproduces the O–H BDE with high accuracy.

Ionisation potential theorem in the presence of the electric field: Assessment of range-separated functional in the reproduction of orbital and excitation energies

Recently, the range-separated density functionals have been reported to reproduce gas phase orbital and excitation energies with good accuracy. In this article, we have revisited the ionisation potential theorem in the presence of external electric field. Numerical results on six linear molecules are presented and the performance of the range-separated density functionals in reproducing highest occupied molecular orbital (HOMO) energies, LUMO energies, HOMO-LUMO gaps in the presence of the external electric field is assessed. In addition, valence and Rydberg excitation energies in the presence of the external electric field are presented. It is found that the range-separated density functionals reproduce orbital and excitation energies accurately in the presence of the electric field. Moreover, we have performed fractional occupation calculation using cubic spline equation and tried to explain the performance of the functional.

Molecules relevant for organic photovoltaics: a range-separated density functional study

Accurate determination of both fundamental and optical gap is necessary for designing molecules relevant for organic photovoltaics. Here, we study how range-separated density functionals reproduce frontier orbital energies, HOMO (highest occupied molecular orbital)–LUMO (lowest unoccupied molecular orbital) gaps, and optical gaps for molecules relevant for organic photovoltaics. In this study, we consider 12 different range-separated density functional for computing HOMO energy, HOMO–LUMO gap, and optical gap which are compared with available experimental and reported GW values. We found that the reproduction of desired photovoltaic properties primarily depend on range separation parameter. Moreover, the tested functionals are comparable with OT-BNL functional.

A new nonempirical tuning scheme with single self-consistent field calculation: Comparison with global and IP-tuned range-separated functional

System‐dependent nonempirical tuning of range‐separated functional provides a way to minimize the delocalization error of the system. However, existing nonempirical tuning method requires the computation of several ΔSCF calculations to determine the optimal μ value. In this article, we have defined a scheme to evaluate the optimal μ value with single self‐consistent field calculation. Our method is based on the evaluation of the spherically symmetric average Electron localization function (ELF) region. According to this scheme, the radius of the spherically symmetric average ELF region gives is a measure of the distance at which the long‐range part of the range‐separated functional becomes dominant. Numerical results indicate that our method improves the reproduction of HOMO energies and HOMO‐LUMO gap in comparison to global and IP‐tuned range‐separated functional. Moreover, in case of HOMO energies, maximum error of the ELF‐tuned functional is considerably smaller than the global and IP‐tuned functional. Furthermore, our method gives considerably smaller deviation of HOMO energies from ΔSCF IP than global range‐separated functional.