Alkynyl bipyridine Pt(II) metallacycles with various combinations of dehydrobenzo[12]annulenes unit ligands showing high third-order nonlinear optical responses

In this work, some triangular monometal complexes and polymetallic alkynyl bipyridine Pt(II) metallacycles are systematically investigated to reveal the effect of the dimensions and combinations of graphyne fragment dehydrobenzo[12]annulene (DBA) modules ligands on the third-order nonlinear optical (NLO) properties via density functional theory. It is found that the insertion of alkynyl- or phenyl-alkynyl into triangular metallacyclic ligand significantly improves the second hyperpolarizability of monometal complexes. Furthermore, the absorption wavelengths are located in the visible region for all complexes, indicating their potential as viable candidates for practical NLO materials. Impressively, the bow-tie type binuclear Pt(II) complex 2a and the linear-shaped trinuclear metallacycle 3a exhibit higher third-order NLO responses compared to other analogues. It is worth noting that the trinuclear Pt(II) metallacycles show significantly large second hyperpolarizabilities up to 35.85 × 10⁵ a.u. and 71.49 × 10⁵ a.u. respectively, which is mainly attributable to small transition energies and the decreased energy gap between the HOMO and LUMO. The take home messages suggest that incorporating intriguing fused DBA ligands into polymetallic complex frameworks is considered an effective method for tuning the third-order NLO responses. Overall, we expect that this study will be helpful in providing valuable guidelines for constructing cost-effective and high-performance organometallic NLO materials.