Intermolecular Interactions as Driving Force of Increasing Multiphoton Absorption in a Perylene Diimide-Based Coordination Polymer

Coordination polymers (CPs) represent an innovative class of materials with proven potential for multiphoton absorption applications. However, understanding the structure-property relationships that govern their nonlinear optical behavior remains challenging. This study presents an in-depth investigation of the effects of intermolecular interactions on multiphoton absorption by focusing on the synthesis and characterization of 1,6,7,12-tetrachloroperylenediimide-N,N'-di-(acetic acid) (H₂tpda) and its coordination with zinc to form [Zn₂tpda(DMA)₂(DMF)_0.3] (Zntpda). How the packing of tpda linkers within the coordination framework influences their optical properties is revealed. The analysis demonstrates that Zntpda exhibits a broadened UV–vis absorption spectrum with no emission indicative of H-type aggregation with additional evidence of a photo-induced electron transfer. Z-scan measurements show enhanced two-photon absorption (2PA) cross-sections of Zntpda compared to H₂tpda and even three-photon absorption (3PA). This is explained by intermolecular interactions, electronic coupling, and spatial confinement effects within the polymer. The findings underscore the critical role of chromophore orientation and packing in optimizing nonlinear optical performance, offering insights for designing advanced functional CP materials tailored for photonic applications.