Side-Chain-Modulated Iminodibenzyl-Based A-D-A Organic Semiconductors for Stable High-Performance Hybrid Photodetectors

Two acceptor–donor–acceptor (A-D-A) small molecules based on an iminodibenzyl (IDB) core were designed and synthesized. Para-cyanophenyl groups were used as terminal acceptors to form symmetric π-conjugated systems promoting intramolecular charge transfer (ICT). The target compounds (A-D-A 1 and A-D-A 2) were obtained in good yields and fully characterized by 1H NMR, 13C NMR, FT-IR, and MS. DFT calculations were performed to investigate their electronic structures and charge-transfer behavior. Hybrid (A-D-A)/n-Si heterojunction devices (D1 and D2) were fabricated and their optoelectronic properties studied. I–V measurements under white light (10–150 mW/cm2) showed that photocurrent increased with illumination intensity. Spectral response at 365, 590, and 850 nm revealed maximum performance in the UV region (365 nm), indicating strong sensitivity to high-energy photons. D1 consistently outperformed D2 across all wavelengths, achieving a responsivity of 2.54 A/W, EQE of 836%, detectivity of 5.51 × 1012 Jones at zero bias, and an ON/OFF ratio of 7.16 × 105. The superior performance of D1 is attributed to improved π-delocalization and balanced LE–CT character. These results demonstrate the potential of IDB-based A-D-A engineering for high-performance UV-enhanced broadband photodetectors.