Chiroptical, linear, and second-order nonlinear optical properties of binaphthol derivatives

Abstract

We have investigated the chiroptical, linear, and second-order nonlinear optical (NLO) properties of seven binaphthol derivatives and elucidated structure–property relationships from the micromechanism for the first time. The excitation energies, oscillator strengths, and rotational strengths of the 150 lowest energy electron excitations for the most stable conformers have been calculated at TDB3LYP/cc-pVDZ level of theory. The experimental UV–vis absorption energies were reproduced well by our calculations. The simulated circular dichroism (CD) spectra and calculated optical rotation (OR) values are in reasonable agreement with experimental ones. These results demonstrate that TDDFT calculations can not only describe the electron transition property but also can be used to assign the absolute configurations (ACs) of binaphthol derivatives with high confidence. Whereas OR values are more sensitive to the molecular structures than CD spectra. The electron transition property and chiroptical origin have been assigned and analyzed. These derivatives possess remarkably large molecular first hyperpolarizabilities, especially compound 7 which has a value of 241.65 × 10⁻³⁰ esu. This value is about 60 times as large as that of highly π-delocalized phenyliminomethyl ferrocene complex. Moreover, compound 6 exhibits pronounced different second-order NLO response values from neutral state to the two cationic states (6²⁺2+2+ and 6⁴⁺4+4+), which indicates that this compound could act as a potential NLO switch material. The cooperativity of intramolecular charge transfer of the studied compounds was also discussed.