Achieving Orange-Red Electrofluorochromism via Aromatic Side-Chain Engineering of Triphenylamine-Cyanostilbene Polymers

Electrochromic (EC)/electrofluorochromic (EFC) bifunctional polymers have attracted significant interest for their ability to precisely modulate dual optical properties in response to electrical signals, positioning them as promising candidates for integrated device applications. This study employs the design and synthesis of a series of EC/EFC bifunctional polymers, incorporating a triphenylamine (TPA) core unit and a cyano diarylethene structure known for its solid-state luminescence properties. The polymers of polymer dye naphtho-type phenylene carbon (PDNPC), polymer dye dibenzo-type phenylene carbon (PDDPC), and polymer dye anthra-type phenylene carbon (PDAPC) each possess biphenyl side chains of differing sizes, namely, naphthalene, anthracene, and pyrene, presenting a unique opportunity to investigate the influence of side-chain steric effects on electro-optical properties. The electrochromic properties of the polymer films exhibited fast switching times, high coloring efficiencies, good cycling stabilities, and strong memory effects. Among these, PDDPC demonstrated the fastest switching time (0.5 s for coloration and 0.6 s for bleaching), high contrast (55.6% at 515 nm), an outstanding coloring efficiency (398.8 cm2/C), and better cycling stability (maintaining 78.4% after 250 cycles at 515 nm). Furthermore, all three polymer films exhibited high fluorescence switch contrast (Ion/Ioff > 100). Notably, PDAPC exhibited an orange-red fluorescence at 589 nm and retained 82.1% of its initial fluorescence contrast after 30 switching cycles. The red-shifted emission is associated with the enlarged fused aromatic substituent and the resulting narrowing of the optical band gap.