Intramolecular boron-locking strategy induced remarkable first hyperpolarizability: role of torsion angles between donor and acceptor units

In conventional strategies to design donor-acceptor (D-A) organic molecules with a large electronic contribution to the first hyperpolarizability ( β ), the effects of the torsion angles ( 1 and 2 ) between donor and acceptor moieties are barely considered. To address this issue, in this work, a promising and novel intramolecular boron-locking strategy combined with the different locking groups of different acceptors to control 1 and 2 , has been proposed to make D-A organic molecules with large β values. Intriguingly, reducing the torsion angles will make the β value of the pyridiny thiophene triphenylamine unit ( Py-Th-TPA ) dramatically increase up to 94%, which is mainly ascribed to the smaller 1 and 2 leading to lower excited energy of the crucial excited state, and enhanced charge transfer (CT) from TPA to Py-Th moieties, and finally greatly increase the donor and acceptor part contributions to β . Correlation between the difference, | 1 − 2 | and β , provides a large coefficient of determination, R 2 = 0.78, which demonstrates that | 1 2 can be regarded as a potential descriptor for designing nonlinear optics (NLO) materials with DA architecture. Clearly, we uncovered that 1 and 2 play a crucial role in the performance of NLO materials with DA fragments. Intramolecular boron-locking strategy with intramolecular noncovalent interactions is a promising and novel strategy for inducing remarkable first hyperpolarizability.