Nickel-Ion-Coordinated Reversibly Solvatochromic Polydiacetylene Based on Tubular Assembly of Macrocyclic Diacetylene

Abstract

Polydiacetylenes (PDAs) present excellent chromogenic characteristics and have been extensively utilized as a sensory polymeric material to design and fabricate colorimetric sensor systems. Herein, we describe a Ni2+-ion-directed reversibly solvatochromic tubular PDA based on macrocyclic diacetylene (MCDA). A dimeric MCDA complex was formed through Ni2+-intercalated coordinative binding with carboxyl groups, which later transform into blue-phase PDA upon UV irradiation. Infrared spectral analysis confirmed the presence of structural water molecules coordinating to central Ni2+, which predicted to fulfill the octahedral geometry. Spectroscopic studies for the reversible blue-red chromatic behavior revealed a very unusual and unprecedented chromatic switching mechanism originating due to localized structural disruption at the Ni2+ coordination site that leads to torsion in the π-conjugated backbone for chromatic changes, in contrast to the typical residual monomeric dissolution-induced mechanism. This unusual behavior can be attributed to the coordinating water molecules, which presents an attractive advantage by creating a hydrophilic pocket at the coordination site and allows interactions with hydrophilic solvents causing structural distortion.