TD-DFT Studies on sp- and sp2-Hybridized Single Vacancy-Defected [60]Fullerene: Electronic Excitation and Nonlinear Optical Properties of C59 [9-4] and C59 [8-5] Isomers

Electron transfer-mediated synergistic nonlinear optical response in the Agn@C18 (n = 4-6) complexes: A DFT study on the electronic structures and optical characteristics

Seeking highly efficient and stable non-linear optical (NLO) materials is crucial yet challenging, given their promising applications in laser diodes and photovoltaics. In this study, we employ the excess electron and charge transfer strategies to theoretically design three novel complexes, namely Agn@C18 (n = 4-6), by adsorbing silver clusters onto the cyclo[18]carbon ring (C18). Our aim is to investigate the NLO characteristics of these complexes using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The results reveal that the adsorption of Ag clusters onto C18 leads to a decrease in excitation energy and an increase in dipole moment and oscillator strengths, thereby significantly enhancing the hyperpolarizability of the complexes. Strikingly, among all these complexes, Ag6@C18 exhibits the highest first hyperpolarizability value of approximately 109496.2620 au calculated at the B3LYP/cc-PVDZ-pp level of theory, which is about 1.3 × 106 times higher than that of pure C18. This finding validates the effectiveness of the proposed strategies in enhancing the NLO response of the species. Moreover, the calculated UV-Vis absorption spectrum demonstrates that the Agn@C18 complexes with excess electrons exhibit absorption at longer wavelengths (ranging from 385 to 731 nm) compared to C18. In addition, the stability, chemical bonding, and charge transfer characteristics of the Agn@C18 (n = 4-6) complexes were also discussed. These findings highlight the potential of these complexes for the development of highly efficient NLO devices.

An investigation into the structural, electronic, and non-linear optical properties in CN (N = 20, 24, 26, 28, 30, 32, 34, 36, and 38) fullerene cages

The present study attempts to investigate the structural, electronic, and non-linear optical properties of C_N (N = 20, 24, 26, 28, 30, 32, 34, 36, and 38) fullerene cages based on Density Functional Theory (DFT). In the DFT calculations, the B3LYP/6-311G(d,p) and CAM-B3LYP/6-311 +  + G(d,p) level of theories were used. The isomers of each fullerene have been received from the Fullerene Structure Library. These isomers have optimized using the B3LYP/6-311G(d,p). The results included optimization of the neutral and ionic state structures according to their multiplicity. Geometries, optimization energies, relative energies, frequencies, HOMO, LUMO, and HOMO-LUMO gap of these stable fullerene cages have been predicted by B3LYP/6-311G(d,p). Afterwards, the most stable structures have been re-optimized using the CAM-B3LYP /6-311 +  + G(d,p). Finally, non-linear optical properties, Fukui functions, density of state, electron affinity, and ionization potential values of the most stable fullerene cages have been found out by the DFT/ CAM-B3LYP /6-311 +  + G(d,p) level of theory. All calculation results have been compared with both C60 fullerene and the relevant literature on corresponding fullerenes.

A two-step MM and QM/MM approach to model AIEE of aryloxy benzothiadiazole derivatives for optoelectronic applications

Aryloxy-benzothiadiazole (ArO-Btz) derivatives show aggregation-induced enhanced emission (AIEE) in the solid-state and are promising candidates for optoelectronic applications. However, understanding the AIEE is a challenging task and is necessary for the rational molecular design of emitters. Therefore, in the present study, electron acceptors (-F, -CN, -NO₂, and -COOH) on the benzothiadiazole ring have been screened for emission in solution and aggregated phases. Herein, we report QM (DFT/TDDFT) and ONIOM (QM/MM) studies on the four ArO-Btz derivatives in comparison with the parent molecule with typical characteristics of AIEE, optoelectronic and non-linear optical properties. Starting from the optimized crystal structure of the parent compound, the structures of the designed clusters have been pre-optimized with MM and then with QM/MM to explore their absorption and emission in the solid phase. The results indicate that in the aggregated phase, the surrounding environment reduces intra-molecular rotations and molecular motion that lead to enhanced emission. Natural bond orbital (NBO) analyses reveal that the ground state structure is stabilized from electron delocalization and operative push-pull effects. Interestingly, nitro-benzothiadiazole exhibits prominent AIEE phenomena, with an emission wavelength beyond 700 nm in solution and in the cluster, reinforced by the magnification of its oscillatory strength by 100 times when aggregated. This dinitro-aryloxy-benzothiadiazole derivative is proposed as a near-infrared emitter for dye-sensitized solar cell, optoelectronic, and non-linear optical applications.

Synthesis, characterization, and theoretical studies of the photovoltaic properties of novel reactive azonitrobenzaldehyde derivatives

All dyes conduct but at different degrees of absorption; it is interesting to study the degree of conductivity and absorptivity of novel reactive azo-dyes in respect to dye-sensitized solar cells (DSSCs) to ascertain their viability for such applications. In this study, four novel reactive azo-dyes were experimentally synthesized from p-aminobenzaldehyde, 4-amino-3-nitrobenzaldehyde, and aniline through series of condensation and coupling reactions. The various functional groups, molecular connectivities, and molecular weight of the various fragments of the synthesized dyes were elucidated using the GC-MS, FT-IR, UV-vis, and NMR respectively. The experimentally determined structures were modeled and investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches to computationally compute the electronic structure properties, reactivity, absorption and solvatochromism in four different phases: gas, ethanol, acetone, and water, and the photovoltaic properties for possible applications in dye-sensitized solar cells (DSSCs). By comparing the HOMO (E_H) and the LUMO (E_L) energies from the results obtained demonstrates that dye D has the highest E_L energy value of −2.48 eV with a relatively lowest E_H energy value of −5.63 eV such that it lies underneath the conduction band edge of TiO₂ which is necessary to enable charge regeneration. Pi-electron delocalization was observed from the natural bond orbital (NBO) calculations between the different aromatic rings with dye B and A having the relatively highest and least second-order stabilization energies between σ* → σ* and LP* → LP interacting orbitals respectively. It is also observed in all the solvents that the Gibbs free energy of injection (ΔG_inject) is greater than 0.2 eV and hence, all the studied azo structures in the four phases provided efficient electron injection and light harvesting efficiency (LHE), however, the value of ΔG_inject for dyes B and D is greatest in all the four phases and thus, provided the highest electron injection of all the dyes. From the fact-findings of quantum theory of atoms-in-molecules (QTAIM), dyes A and C have extra-stability due to their relatively high numbers of intramolecular H-bond interactions along with some additional intra-atomic bonding between atoms within the studied compounds. Hence, all the four dyes are good for DSSCs applications.

Four novel reactive azo-dyes were experimentally synthesized from p-aminobenzaldehyde, 4-amino-3-nitrobenzaldehyde, and aniline through series of condensation and coupling reactions, and their properties were assessed for possible application in dye-sensitized solar cells.

Synthesis, characterization, DFT, and TD-DFT studies of (E)-5-((4,6-dichloro-1,3,5-triazin-2-yl)amino)-4-hydroxy-3-(phenyldiazenyl)naphthalene-2,7-diylbis(hydrogen sulfite)

In this study, (E)-5-((4,6-dichloro-1,3,5-triazin-2-yl)amino)-4-hydroxy-3-(phenyldiazenyl)naphthalene-2,7-diylbis(hydrogen sulfite), a cyanurated H-acid (CHA) azo dye, was synthesized and characterized using FT-IR spectrophotometer and GC-MS spectroscopy. A density functional theory (DFT) based B3LYP and CAM-B3LYP method with 6–311 + G (d,p) basis set analysis was computed for HOMO-LUMO, natural bonding orbitals (NBO), UV-Vis absorptions and excitation interactions, in order to understand its molecular orbital excitation properties. A low Energy gap (Eg) of 2.947 eV was obtained from the molecular orbital analysis, which showed that HOMO to LUMO transition is highly feasible; hence CHA is adequate for diverse electronic and optic applications. Studies of the first five excitations (S0 → S1/S2/S3/S4/S5) of CHA revealed that S0 → S1 and S0 → S3 are π → π* type local excitations distributed around the –N=N– group; S0 → S2, a Rydberg type local excitation; S0 → S4, a highly localized π → π* excitation; while S0 → S5 is an n → π* charge transfer from a benzene ring to –N=N– group. From NBO analysis, we obtained the various donor–acceptor orbital interactions contributing to the stabilization of the studied compound. Most significantly, some strong hyper-conjugations (n → n*) within fragments, and non-bondingand anti-bonding intermolecular (n → n*/π* and π → n*/π*) interactions were observed to contribute appreciable energies. This study is valuable for understanding the molecular properties of the azo dyes compounds and for synthesizing new ones in the future.