The Green Box: Selenoviologen-Based Tetracationic Cyclophane for Electrochromism, Host-Guest Interactions, and Visible-Light Photocatalysis

The novel selenoviologen-based tetracationic cyclophanes (green boxes 3 and 5) with rigid electron-deficient cavities are synthesized via SN2 reactions in two steps. The green boxes exhibit good redox properties, narrow energy gaps, and strong absorption in the visible range (370-470 nm), especially for the green box 5 containing two selenoviologen (SeV2+) units. Meanwhile, the femtosecond transient absorption (fs-TA) reveals that the green boxes have a stabilized dicationic biradical, high efficiency of intramolecular charge transfer (ICT), and long-lived charge separation state due to the formation of cyclophane structure. Based on the excellent photo physical and redox properties, the green boxes are applied to electrochromic devices (ECDs) and visible-light-driven hydrogen production with a high H2 generation rate (34 mu mol/h), turnover number (203), and apparent quantum yield (5.33 x 10-2). In addition, the host-guest recognitions are demonstrated between the green boxes and electron-rich guests (e.g., G1:1-naphthol and G2:platinum(II)-tethered naphthalene) in MeCN through C-H center dot center dot center dot ir and ir center dot center dot center dot ir interactions. As a one-component system, the host- guest complexes of green box superset of G2 are successfully applied to visible-light photocatalytic hydrogen production due to the intramolecular electron transfer (IET) between platinum(II) of G2 and SeV2+ of the green box, which provides a simplified system for solar energy conversion.

Automated summary

Selenoviologen-based tetracationic cyclophanes with rigid electron-deficient cavities were synthesized through SN2 reactions. These cyclophanes exhibit good redox properties, narrow energy gaps, and strong absorption in the visible range. They were successfully applied to electrochromic devices and visible-light-driven hydrogen production. Host-guest recognitions were demonstrated, and a simplified system for solar energy conversion was achieved.