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 photophysical 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
μmol/h), turnover number (203), and apparent quantum yield (5.33
× 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···π and
π···π interactions. As a one-component
system, the host–guest complexes of green box⊃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.