Halogen-assisted colour modulation in a flexible copper coordination polymer crystal-based hybrid photonic splitter

Abstract

Tuning the optical band in flexible nano- and micro-crystalline structures using halogen atoms offers a promising route for fabricating functionally complex soft optical devices, though it remains a significant challenge. Herein, we report the synthesis and crystallization of two high aspect-ratio, elastic, and chromatically distinct one-dimensional coordination polymer (CP) crystal waveguides: the cyan-emissive poly-[di-μ-iodido-bis[3,5-dibromopyridine]dicopper(I)] (CuDBP) and the green-emissive poly-[di-μ-iodido-bis[3-bromo-5-chloropyridine]dicopper(I)] (CuBCP). Theoretical studies have revealed a noticeable difference in the optical energy gap of these halogen-substituted CPs. Mechanical micromanipulation of these low-optical-loss crystal waveguides using an atomic force microscopy (AFM) cantilever tip reveals their pseudoplasticity, enabling the fabrication of an innovative three-port hybrid Y-splitter. This circuit operates as a passive optical splitter when the input is introduced through the CuBCP crystal, whereas it functions as a chromatic signal modulator without splitting when the input originates from the CuDBP crystal. Demonstrating such unique and unexplored properties of 1D CPs in photonic components corroborates the versatility for devising next-gen organic photonic integrated circuits.