Optimizing nonlinear optical and photovoltaic performance in butterfly-shaped carbazole vs. borole derivatives: An...

Nonlinear optical (NLO) materials play a crucial role in various hi-tech optoelectronic applications, driving the quest for novel molecular frameworks with superior properties. In this context, this study systematically explores derivatives of phenanthrene-carbazole and phenyleno-borole, aiming to finely tune their NLO properties by incorporating multiple push-pull groups at their molecular periphery. The integration of these push-pull groups with the central core significantly enhances intramolecular charge transfer (ICT) within the molecular structures, leading to improved optical and NLO properties. Our findings highlight compound 3-PB as a standout among the designated compounds, exhibiting exceptional linear optical properties with the maximum linear isotropic (α_iso) value of 95.77 × 10^-24 esu and a maximum anisotropic (α_aniso) of 106.6 × 10^-24 esu. Notably, it also shows an impressive average static third-order NLO polarizability <γ> amplitude of 574.1 × 10^-36 esu. A comparative study reveals that the <γ> amplitude of 3-PB is ∼78 times greater than p-NA (7.29 × 10^-36 esu) at the M06/6-311G∗∗ level of theory. TD-DFT computations further attribute the remarkable NLO response of 3-PB to its lower transition energy, setting it apart from the other designated molecular systems. Additionally, TD-DFT calculations explored structure-NLO property relations through FMOs, DOS, and MEP maps. A detailed comparison of NLO polarizabilities and electronic properties highlights the significance of carbazole and borole-based systems in achieving strong NLO responses. Notably, compound 3-PB exhibits enhanced NLO properties due to the presence of polyaromatic rings and a boron atom serving as an acceptor, along with dimethylamine (donor group) substitutions at the periphery of the molecule. Beyond exceptional NLO performance, our entitled systems also demonstrate favorable photovoltaic potential. Specifically, compound 3-PB exhibits the highest LHE value of 0.999. Additionally, open circuit voltage values range from 1.55 to 3.02 eV, while lower ΔG_reg values suggest that these compounds are promising candidates for sensitizing DSSC performance.