Design and synthesis of a fused porphyrin dimer for enhanced visible-to-near-infrared-driven photocatalytic hydrogen evolution

Abstract

A new acceptor–linker–donor–linker–acceptor (A–π–D–π–A) structured porphyrin dimer, F-C19ZnP, was designed and synthesized as a visible-to-near-infrared (Vis-NIR) light-harvesting photosensitizer for photocatalytic hydrogen evolution (PHE). F-C19ZnP features a bimetallic Zn(II)-coordinated fused porphyrin dimer as the donor, a phenylene–ethynylene π-linker, and a 3-ethylrhodanine acceptor. Its photophysical, electrochemical, thermal, and morphological properties, as well as photocurrent response, water contact angle, and PHE performance, were systematically investigated and compared with those of C19ZnP, a structurally similar monometallic porphyrin. Density functional theory calculations provided further insight into the optoelectronic and charge separation characteristics of both porphyrins. F-C19ZnP exhibited markedly broader light absorption (400–1100 nm) and stronger Vis-NIR light-harvesting ability than C19ZnP. F-C19ZnP also exhibits a higher surface area and a larger pore size than C19ZnP, providing more accessible channels for electron transport. It also showed a longer photoexcited electron lifetime (4.9 ns vs. 2.1 ns), enabling more efficient electron transfer to water and resulting in enhanced PHE performance. F-C19ZnP demonstrated a higher photocurrent response, signifying improved charge separation and transport. Its lower water contact angle, attributed to its well-dispersed 300 nm nanosphere morphology, enabled better interfacial interaction with water. Under optimized PHE conditions, F-C19ZnP achieved a PHE rate (ηH₂) of 7.93 mmol g⁻¹ h⁻¹, which is eight times higher than that of C19ZnP (1.01 mmol g⁻¹ h⁻¹), and outperformed C19ZnP at all tested irradiation wavelengths (420, 630, and 810 nm). Furthermore, F-C19ZnP displayed excellent photostability and reusability. As the first Vis-NIR fused porphyrin dimer for efficient PHE, F-C19ZnP paves a promising path for the development of advanced porphyrin-based photosensitizers.