A theoretical approach for exploration of non-linear optical amplification of fused azacycle donor based thiophene polymer functionalized chromophores

The quantum chemical calculations are executed for a series of designed carbazole-based oligothiophene systems (CPTR1 and CPTD2-CPTD8) having D₁-π₁-D₂-π₂-A architecture. The effect of addition of π-linkers on designed architecture for the electronic and non-linear optical response was examined at M06/6-311G(d,p) level of theory. The frontier molecular orbitals (FMOs), density of states (DOS), natural population analysis (NPA), UV–Vis and transition density matrix (TDM) and non-linear optical (NLO) analyses were utilized in order to comprehend key electronic and non-linear optical response. All the designed molecules exhibited a lower energy gap (E_LUMO-E_HOMO) as 2.434–2.780 eV, as compared to the CPTR1 (2.875 eV). Among all the derivatives, CPTD8 exhibited the highest dipole polarizability 〈α〉 and second hyperpolarizability (γ_tot) as 2.946 × 10^-22 esu and 41.372 × 10^-33 esu, respectively. Dipole moment (µ) and first hyperpolarizability (β_tot) of CPTD8 were found to be as 3.478 D and 118.886 × 10^-29 esu, correspondingly. The second hyperpolarizability (γ_tot) of CPTD8 was observed to be ∼6.4 ∼4.0 ∼2.5 ∼1.8 ∼1.4 ∼1.3 and ∼1.1 times higher in comparison to CPTR1 and CPTD2-CPTD7, respectively. It is concluded that carbazole-based oligothiophene might be used as a potential material in optoelectronic devices.     

Exploration of nonlinear optical behavior in asymmetric dithieno [3,2b:2′,3′d] pyrrole based push pull constrain: A theoretical approach

The organic compounds with end-capped acceptors obtained much consideration in optoelectronic field owing to their promising electronic properties. Herein, a series of PTMD1-PTMD6 conjugated compounds having D-π-A architecture were designed via structural tailoring including end-capped acceptors in non-fullerene compound (PTMR). The PTMR and its designed compounds were used at M06/6-311G(d,p) level for their optimization analysis and subsequently, by using optimized geometries to perform non-linear optical (NLO), frontier molecular orbitals (FMOs) and natural bond orbitals (NBOs) analyses. The quantum chemical investigations revealed that all the designed compounds showed significant reduction in band gaps with the range of 1.467–1.880 eV in comparison to PTMR (2.308 eV). The band gaps were found as PTMR (2.308) > PTMD6 (1.880) > PTMD1 (1.752) > PTMD2 (1.693) > PTMD4 (1.532) > PTMD5 (1.514) > PTMD3 (1.467) with eV in the descending order. Further, density of states (DOS) supported the results of FMOs study, consequently, according to transition density matrix (TDMs), the designed chromophores (PTMD1-PTMD6) displayed the transmission of charge effectively. The PTMD3 showed the maximum value of λ_max at 764.627 nm as compared to all the designed derivatives with greater bathochromic shift. The compound PTMD3 showed the highest values of β_tot and < γ > among all the studied compounds i.e., 7.695 × 10^-27 and 1.776 × 10^-31 esu, respectively. According to theoretical investigation, the structural modification with different acceptor moieties played an important role in the context of desirable NLO materials for optoelectronic applications.     

Exploring high pressure structural transformations,electronic properties and superconducting properties of MH2 (M = Nb,Ta)

The high-pressure structures and properties of MH₂ (M = Nb, Ta) are explored through an ab initio evolutionary algorithm for crystal structure prediction and first-principles calculations. It is found that NbH₂ undergoes a phase transition from a cubic Fm$\overline{3}$m structure with regular NbH₈ cubes to an orthorhombic Pnma structure with fascinating distorted NbH₉ tetrakaidecahedrons at 48.8 GPa, while the phase transition pressure of TaH₂ from a hexagonal P6₃mc phase with slightly distorted TaH₇ decahedron to an orthorhombic Pnma phase with attractive distorted TaH₉ tetrakaidecahedrons is about 90.0 GPa. Besides, the calculated electronic band structure and density of states demonstrate that all of these structures are metallic. The Poisson’s ratio, electron localization function, and Bader charge analysis suggest that these phases possess dominant ionic bonding character with the effective charges transferring from the metal atom to H. From our electron–phonon calculations, the calculated superconducting critical temperature T_c of the Pnma-NbH₂ is 6.903 K at 50 GPa. Finally, via the quasi-harmonic approximation method, the phase diagrams at pressure up to 300 GPa and temperature up to 1000 K of MH₂ (M = Nb, Ta) are established, where the transition pressure of Fm$\overline{3}$m-NbH₂ → Pnma-NbH₂ and P6₃mc-TaH₂ → Pnma-TaH₂ were found to decrease with increasing temperature.     

Influence of acceptor tethering on the performance of nonlinear optical properties for pyrene-based materials with A-π-D-π-D architecture

In this study, we designed a series of pyrene-based donor-π-donor-π-acceptor compounds (HPTC1-HPTC7) by structural tailoring the reference compound (HPTC) using acceptor units. Nonlinear optical (NLO) properties, frontier molecular orbitals (FMOs), natural bonding orbital (NBO), transition density matric (TDM) analysis, and absorption spectra of reference and proposed derivatives were calculated at M06/6-31G(d,p) functional. All the designed compounds have smaller energy bandgaps than the HPTC compound. Moreover, the designed compounds exhibited larger global softness values than the reference. The absorption maxima of HPTC2, HPTC3, and HPTC7 are blue shifted with respect to HPTC. NBO analysis revealed that prolonged hyper conjugative associations and strong interactions between the donor (π) and acceptor (π*) moieties play a crucial part in their stabilization. The FMO and NBO findings supported the NLO responses of entitled compounds, and consequently, the linear and nonlinear properties of designed derivatives elevate compared to the reference molecule. Promisingly, the NLO response for HPTC7 comprises of highest values of <α>, β_total and < γ > as 1.92 × 10^?22 esu, 1.95 × 10^?27 esu, and 4.69 × 10⁷ (a.u). This NLO behavior shows push–pull NLO chromophores for HPTC7 predicting its role in pursuing NLO materials for optoelectronic applications.