Redox- and Photo-Controlled CO ₂ Capture at Cooperative Quinone Rhenium Sites

A hybrid photo- and electroactive material combining chitosan and a quinone-based rhenium complex was prepared to investigate reversible CO2 binding under redox and photochemical control. Chitosan obtained from shrimp-shell chitin was functionalized with 4-pyridinecarboxaldehyde to introduce pyridinic coordination sites, enabling the coordination-mediated incorporation of a Re(I)(CO)3(1,10-phenanthroline-5,6-dione) fragment into the polymer matrix. Cyclic voltammetry of the molecular reference complex shows two ligand-centered reduction processes associated with the phendione unit. Upon CO2 introduction, the second reduction undergoes an anodic shift consistent with reversible interaction between the reduced quinonoid site and CO2. Analysis of the potential shifts affords a binding constant of log K = 5.1 for the molecular complex. When incorporated within the chitosan matrix, the system exhibits a substantially higher apparent affinity (log K = 8.3) within the same electrochemical framework, indicating polymer-mediated modulation of the CO2 interaction. Under visible irradiation (410 nm), the immobilized complex remains photoactive and displays a CO2-dependent spectroscopic response. TD-DFT calculations support these observations and assign the dominant spectral changes to metal-to-ligand charge-transfer transitions involving the quinone motif. Overall, the results demonstrate that integration of quinone–rhenium units within a biopolymeric chitosan matrix preserves redox and photoactivity while modulating the apparent CO2 affinity, providing a multifunctional platform for electrically and light-driven carbon capture.