Reticular design and alkyne bridge engineering in donor–π–acceptor type conjugated microporous polymers for boosting photocatalytic hydrogen evolution

Abstract

Conjugated microporous polymers (CMPs) have gained increased significance as crucial components in the field of photocatalytic H₂ production due to their excellent ultraviolet-visible (UV-vis), and robust fluorescence. Herein, we used two types of reaction approaches including Suzuki and Sonogashira–Hagihara coupling to prepare six different types of CMPs for the first time to investigate and understand the reactivity of triphenylamine (TPA) and alkyne group linked CMPs for photocatalytic H₂ evolution from H₂O. Six different TPA-based CMPs including TPA–TPA (D–D), TPE–TPA (A–D), Py–TPA (A–D), TPA–TB–TPA (D–π–D), TPE–TB–TPA (D–π–A), and Py–TB–TPA (D–π–A) CMPs have been designed and synthesized via Suzuki and Sonogashira–Hagihara coupling reaction, respectively. Our investigation of TPA–CMP materials showed that TPA–TPA, Py–TPA, and TPA–TB–TPA CMPs exhibited elevated T_d10 values, measuring 557 °C, 508 °C, and 482 °C, respectively. Additionally, based on the results of thermal gravimetric analysis (TGA) and nitrogen adsorption–desorption measurements, these CMPs displayed specific surface areas (S_BET) of 98, 913, and 459 m² g⁻¹, respectively. Furthermore, in the order presented, the Py–TPA, and Py–TB–TPA CMPs showcase hydrogen evolution rate (HER) values of 3633, and 16 700 μmol g⁻¹ h⁻¹, respectively. As per density functional theory (DFT) calculations, the presence of an alkyne bridge in the Py–TB–TPA CMP can effectively hinder electron–hole recombination, prolong the lifetime of charge carriers, and improve the efficiency of their transfer and separation when compared to a similar CMP (Py–TPA CMP) lacking an alkynyl group. As a result, including an alkynyl (π) bridge in the polymers led to an augmentation in their photocatalytic activity. This work presents various viewpoints regarding the development and architecture of high-performance CMPs incorporating alkynyl groups, showcasing their potential applications in photocatalysis.