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 (beta), the effects of the torsion angles (theta 1 and theta 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 theta 1 and theta 2, has been proposed to make D-A organic molecules with large beta values. Intriguingly, reducing the torsion angles will make the beta value of the pyridiny thiophene triphenylamine unit (Py-Th-TPA) dramatically increase up to 94%, which is mainly ascribed to the smaller theta 1 and theta 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 beta. Correlation between the difference, |theta 1 - theta 2| and beta, provides a large coefficient of determination, R2 = 0.78, which demonstrates that |theta 1 - theta 2| can be regarded as a potential descriptor for designing nonlinear optics (NLO) materials with D-A architecture. Clearly, we uncovered that theta 1 and theta 2 play a crucial role in the performance of NLO materials with D-A fragments. Intramolecular boron-locking strategy with intramolecular noncovalent interactions is a promising and novel strategy for inducing remarkable first hyperpolarizability.