Selenoviologen-Appendant Metallacycles with Highly Stable Radical Cations and Long-Lived Charge Separation States for Electrochromism and Photocatalysis

Two coordinated metallacycles (rhomboid for M1, hexagonal for M2) with selenoviologens (SeV2+) pendants were synthesized via coordination-driven hierarchical self-assembly. M1/M2 with rigid and discrete metallacyclic cores showed tunable optoelectronic properties due to strong pi-pi stacking and push-pull electron structures. Femtosecond transient absorption (fs-TA) revealed that the formation of macrocyclic structure can not only enhance the stability of radical cation, but also improve the efficiency of intramolecular charge transfer and produce a long-lived charge separation state. The electrochromic performances of M1/M2-based devices were exhibited to show decent radical stabilization. By using M1/M2 as the photocatalyst, the improved catalytic efficiency (>80 %) of visible-light-induced cross-dehydrogenative coupling (CDC) reactions was achieved due to the highly stable radical cations and long-lived charge separation states, which were also confirmed by fs-TA.