Energy band gap modulation and photoinduced electron transfer fluorescence sensing properties of D–A conjugated polymers containing benzotriazole

Two new conjugated polymers containing benzotriazole were synthesized via Suzuki coupling reaction, and the polymer with lower energy band gap was created by designing the structure of the acceptor unit by introducing thiophene unit at both ends of the benzotriazole. Surprisingly, the fluorescence emission of D–A conjugated polymer with modified unit shifted from blue to yellow light, and the polymer had a higher fluorescence quantum efficiency. In addition, thiophen benzimidazole was introduced as the side chain unit for the study of photoinduced electron transfer (PET) mechanism. The addition of Fe³⁺ and Cu²⁺ caused significant quenching of fluorescence of polymers, and the polymer with high energy band gap exhibited higher fluorescence quenching ability. Moreover, when exploring the fluorescence sensing of [P‐Fe³⁺] complex in the presence of anion, it was observed that the PO₄³⁻ competed with [P‐Fe³⁺] complex for Fe³⁺, interrupting the fluorescence sensing mechanism eventually leading to the recovery of fluorescence. The design approach utilized in this survey for D–A conjugated polymer paves the way for a novel mean of functional control of fluorescence sensor based on PET fluorescence sensing.