Quantum Chemical Prediction of Nonlinear Optical and Photovoltaic Properties in Linear and Bent Configurations of Carbazole/Borole Derivatives

In this study, we conducted a comparative quantum computational investigation about carbazole/borole derivatives to understand how different configurations like linear and bent, and terminal groups can affect their linear and second hyperpolarizability properties. The goal was to compare the optical and NLO response properties, photovoltaic parameters and charge transfer properties of these linear/bent configurations. Among all the designed compounds the linear compounds exhibited larger linear isotropic and anisotropic polarizability and second hyperpolarizability amplitudes (γ) compared to the bent compounds. The highest values of isotropic polarizability of Py-1L and Py-2L are calculated to be 109.0 × 10^–24 esu and 103.9 × 10^–24 esu, respectively. Notably, linear configurations Py-1L and Py-2L achieved the γ amplitudes as high as 840.1 × 10⁻³⁶ esu and 776.9 × 10⁻³⁶ esu. When compared to the prototype para-nitroaniline (p-NA) molecule, these amplitudes are found to be ~ 115 times and ~ 113 times larger than p-NA as calculated at the same level of theory. Moreover, TD-DFT calculations also revealed that linear configuration gave better NLO response due to their higher oscillator strengths, dipole moment changes between ground and excited states and lower transition energy values among all the designed compounds. Frontier molecular orbitals, molecular electrostatic potential map, electron density difference and natural bond orbitals analysis indicated that more efficient intramolecular charge transfer in linear configuration, leading to high NLO response than bent configuration. The highest light harvesting efficiencies have been exhibited by Py-1L and Py-2L, with values of 0.928 eV and 0.903 eV, respectively. Overall, the current systematic comparison of NLO polarizabilities and other electronic properties emphasized the importance of configuration-based designs for achieving high performance NLO response properties in the designed compounds.