The [2+2] cycloaddition–retroelectrocyclization (CA–RE) between N,N‐dialkylaniline‐substituted alkynes and 7,7,8,8‐tetracyanoquinodimethane (TCNQ) is employed to fabricate functional cross‐linked polymer films containing the intramolecular charge‐transfer (CT) chromophores at the cross‐linking points. Polystyrene bearing N,N‐dialkylaniline‐substituted alkynes (P1) and TCNQ polyester (P2) are mixed in tetrahydrofuran (THF), then this solution is spray‐coated onto an indium tin oxide or glass plate. Heating to 100 °C initiates the [2+2] CA‐RE reaction, resulting in the formation of cross‐linked polymer films. The reaction progress and completion are evaluated by monitoring the CT absorption band and cyano vibration peaks. The resulting cross‐linked polymer films show reversible cathodic electrochromism between the neutral and anion radical states. In addition, they also display the visual detection behavior of protic acids and Lewis acids, such as Ag+ ions. Accordingly, the Ag+ ion‐loaded polymer films are prepared, and their antibacterial activities are studied. As more Ag+ ions are loaded, the CT band more bathochromically shifts and more potent antibacterial activities are obtained. Therefore, the antibacterial activity of the polymer films can be visually recognized by the film colors. Furthermore, the loaded Ag+ ions can be released from the polymer films by application of an electrochemical potential.