M.Phil / MS

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Effect of Electric Field Variation on Electronic and Nonlinear Optical (NLO) Properties of Ionic Liquids: A DFT Study
(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-27) Dua Fatima; SP22-R06-018; Dr. Mazhar Amjad Gilani; LHR TP 8657
The growing use of nonlinear optical (NLO) materials in various fields has generated interest in designing innovative smart NLO materials. This study focuses on three specific ionic liquids, where the same cation, 1-ethyl-3-methyl imidazolium, is combined with three different anions (Br-, C-, F-). The study explores the effects of External Electric Field (EEFs) on these three ILs using Density Functional Theory (DFT) calculations. The interaction energies calculated confirm the stability of the newly designed ILs. Applying external electric field (EEFs) ranging from 0.001 a.u to 0.006 a.u leads to a significant reduction in the E(H–L) gap, and the lowest energy gap of 4.43 eV is observed in EMIBr at field strength of 0.006 a.u. Natural Bond Orbital (NBO) analysis validates substantial charge transfer from cations to anions, with the highest transfer observed in EMIBr. External Electric field enhances the first hyperpolarizability, and EMIBr exhibits the highest value i.e 1828 a.u at 0.006 a.u. TD-DFT calculations are executed to derive electronic states influenced by an external electric field (EEF), and the highest λmax (nm) i.e. 227 nm, is observed in the case of EMIBr at 0.006 a.u. The study also determines frequency-dependent Second Harmonic Generation (SHG) and Electric-Optical Pockels Effect (EOPE), with noteworthy values observed i.e 2.0×103 and 9.8×103 respectively in case of EMIBr. In conclusion, the study provides guidelines for computationally designing efficient and thermodynamically stable complexes for optical and optoelectronic technologies. The proposed ILs could find potential applications in new electronic devices, contributing to the development of advanced NLO materials.
Theoretical Assessment of Corannulene-Based Aggregates as High-Performance Nonlinear Optical Materials
(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-27) Sobia Waheed; SP22-R06-024; Dr. Mazhar Amjad Gilani; LHR TP 8662
The growing use of nonlinear optical (NLO) materials in various fields has generated interest in designing innovative smart NLO materials. This study focuses on enhancing the nonlinear optical response through doping of alkali metals on the corannulene (C20H10) dimer through Density Functional Theory (DFT) calculations. The interaction energies calculated computationally confirm the stability of the newly designed alkali metal-doped cncx dimers. Alkali metal doping, particularly with Li, Na, and K, leads to a significant reduction in the E(H–L) gap, and the lowest energy gap of 3.17 eV is observed in K-doped cncx dimer. The TD-DFT study shows that these alkali metal doped complexes have λmax in the visible regions(568-576nm). Total density of states (TDOS) spectra support the involvement of dimer in forming new Highest Occupied Molecular Orbital (HOMO). Natural Bond Orbital (NBO) analysis validates substantial charge transfer from alkali metals to dimer, with the highest charge transfer (0.938 |e|) observed in the K@cncx complex. Doping with alkali metals enhances the first hyperpolarizability, and Li@cncx exhibits the highest value (9.3×104 au). The study also determines frequency-dependent Second Harmonic Generation (SHG), Electric-Optical Pockels Effect (EOPE), electro-optic dc-Kerr effect (EOKE). The value of 3.4×104 au is observed for SHG, while for EOPE the value is 4.6×105 au. A significantly enhanced EOKE value (1.0 × 1010 au) is shown by Na@cncx. Additionally, these structures exhibit a high nonlinear quadratic refractive index (a maximum value of 9.9×10-18cm2 W-1). In conclusion, the study provides guidelines for computationally designing efficient and thermodynamically stable complexes for optical and optoelectronic technologies.
Exploration of Diradical Graphene Nanoflakes (GNFs) as NLO based Sensors for NOx
(Library Information Services COMSATS University Islamabad Lahore Campus, 2023-02-27) Mawra Nasir; SP22-R06-009; Dr. Mazhar Amjad Gilani; LHR TP 8648
Approximately 78% of the air is composed of nitrogen, which, in its elemental form, is not harmful. However, nitrogen oxides (NO, NO2, N2O) present in the air can have adverse effects on both human health and the environment. In the realm of environmental monitoring, the crucial task of adsorbing or detecting small (toxic) gas molecules relies on appropriate semiconductors. Although graphene nanoflakes (GNFs) find extensive applications in energy storage and optoelectronics, their potential as sensors is not extensively explored. This study investigates the adsorption of nitrogen-containing gaseous molecules i.e NO, NO2, and N2O on trigonal, rhombic, and bowtie GNFs sheets through Density Functional Theory (DFT) simulations. The analysis encompasses optimized geometries, adsorption energies, as well as Natural Bond Orbital (NBO) and Electron Density Differences (EDD) analyses to interpret the interaction between GNFs sheets and NOx gases. The theoretical findings reveal strong binding between GNFs sheets and NO2 molecule, with adsorption energies of -30.2, - 17.1, and -29.8 kcalmol-1 for NO2@t-GNFs, NO2@r-GNFs, and NO2@b-GNFs, respectively. Furthermore, Frontier Molecular Orbital (FMO), and Density of State (DOS) analyses underscore the significant impact of gas adsorption on GNF sheets. Interaction Region Indicator (IRI) and Quantum Theory of Atoms in Molecules (QTAIM) analyses indicate the covalent interactions between GNFs sheets and NO, NO2 gases, while van der Waals interactions are confirmed with N2O gases. UV-Vis and IR analyses demonstrate the selectivity of b-GNFs towards NO2 and NO, respectively. Based on Nonlinear Optical (NLO) response, b-GNFs exhibit the highest sensitivity towards NOx. In conclusion, GNFs sheets exhibit promising sensitivity to gaseous molecules, positioning them as potential multimode sensors, including UV, IR, and NLO-based applications. This theoretical insight aids experimentalists in developing novel GNFs-based sensors for the detection of toxic gases.

M.Phil / MS

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