Quantum chemical framework for designing high-performance ladder-shape NLO molecules and study of implicit vs explicit solvent effects on their NLO properties.

[Display omitted] • Ladder-shape 7[helicene] derivatives were designed for efficient NLO response. • A larger NLO for [7]HC-5 is attributed to its lowest transition energy of 3.31 eV. • Unlike PCM solvation method, the gas and explicit salvation methods show good agreements. • Frequency-dependent γ values revealed that derivatives are suitable for wide range of frequency. • For photovoltaic applications, the V oc and ΔG reg for [7]HC-5 are found to be 2.71 and 0.06 eV. Researchers in materials science are greatly fascinated by helicene chemistry due to its excellent optical and structural properties. In this work, we introduced symmetrical substitution of donor and acceptor groups on the [7]helicene ([7]HC-1 to [7]HC-5). DFT analysis is used to explore nonlinear optical (NLO) response for designed compounds. For [7]HC-5 , the linear isotropic (α iso) and anisotropic polarizability (α aniso) are 31.59 × 10−24 esu and 59.86 × 10−24 esu, respectively. [7]HC-5 has the highest average third-order NLO polarizability (<γ>) of 47.24 × 10−36 esu which is approximately six times greater than that of para -nitroaniline, a well-known prototype NLO molecule. The effect of implicit and explicit solvents on <γ> and α iso of three selected compounds ([7]HC-1 , [7]HC-3 , and [7]HC-5) is also evaluated. As compared to explicit and gas phase methods, PCM model predicts an overestimation by an increment of ∼ 4-5 times for selected compounds. TD-DFT calculations show a higher transition dipole moment (4.24) and a lower transition energy (3.414 eV) for [7]HC-5. The higher NLO response is explained based on frontier molecular orbitals (FMOs), electron density difference (EDD), and molecular electrostatic potentials (MEPs). There is a red shift for studied compounds based on UV-visible results. The C-N stretching at 1372 cm-1 for [7]HC-5 indicates the presence of -N(CH 3) 2. Additionally, we studied photovoltaic parameters and found that [7]HC-5 has the maximum open circuit voltage and the lowest dye regeneration of 2.71 eV and 0.06 eV, respectively. [ABSTRACT FROM AUTHOR]