Novel cyclic and linearizing cyclic Pd(II) nanohoop-based cordination complexes achieving nonlinear optical activity transparency trade-off optimization

Abstract

In this work, we systematically designed and comparatively analyzed the geometric structures, electronic absorption spectra, polarizabilities, first hyperpolarizability (βtot) and dynamic hyper-Rayleigh scattering response of circular Pd(II)-nanohoop complexes with 2,2′-bipyridine-embedded CPPs ligand and curved complexes decorated with alkyl tether accompanied by linear counterparts via quantum chemical calculations. Correlating results demonstrated that in comparison to conventional linear species, nanohoop ligand coordinated with metal Pd(II) can achieve remarkably improved quadratic nonlinear optical (NLO) coefficient, whereas are not accompanied by a certain degree of bathochromic shift in the absorption band. This phenomenon effectively overcomes the trade-off between good transparency and high second-order NLO response. Intriguingly, alkyl tether modified curved complexes own the largest quadratic NLO responses in our case, even the conjugation is broken by alkyl chain modified. Noteworthily, further extending phenylene backbone will not yield any positive effect on the enhancement of their βtot values for circular and linear systems once the number of phenylene reaches a certain degree, suggesting that size-dependent effect can be deemed to an effective approach to obtain the desired NLO response. Additionally, the polarizable environment has a significant influence on second-order NLO behavior, especially an accelerated trend changing from gas phase to solid phase. Overall, we hope these results can enrich the cognition into the NLO structure-function correlations based on metal nanohoop complexes and provide new avenue toward coping with trade-off between good transparency and high NLO performance.