Modulation of Circularly Polarized Luminescence by Vaulting Polymethylene Bridges in Planar Chiral <i>trans</i> ‐Bis(2‐iminomethylpyrrolato)platinum(II) Complexes

In this study, we investigated the chain-length dependence of circular dichroism (CD) and circularly polarized luminescence (CPL) properties of trans-bis(2-iminomethylpyrrolato)platinum(II) complexes (1a-d) featuring polymethylene-chain bridges that vaulted across the platinum center. These complexes are almost non-emissive in solution or in PMMA films; however, when dispersed in β-estradiol as a host matrix, their emission quantum yields increase markedly, enabling direct comparison of their CPL characteristics and correlation with molecular structure. Systematic variation of the vaulted chain length revealed that the anisotropy factors (g values) of both CD and CPL (g_abs and g_em) vary as a function of the chain length. DFT-optimized geometries indicated that complexes with shorter vaulted chains exhibit greater bending and torsional distortion between the two 2-iminomethylpyrrolate ligand planes. These structural distortions modulate the angle θ_e,m between the electric and magnetic transition dipole moments (µ_e and µ_m), thereby governing the observed g-value changes. This study demonstrates that precise control of the vaulted chain length enables molecular-level tuning of structural distortion and chiroptical responses in platinum(II) complexes, providing a new design strategy for highly efficient and structurally tunable CPL materials.