Photochromic Semiconductive Hydrogen-Bonded Organic Framework (HOF) with Broadband Absorption

Semiconductors
with broadband photoelectric response have important
practical needs in many aspects such as solar energy conversion, photocatalysis,
and photodetection. We synthesized the first photochromic semiconductive
hydrogen-bonded organic framework (HOF), [H2(bpyb)]­(H2PO4)2·2H2O (1), using the polycyclic viologen cation [H2(bpyb)] (bpyb
= 1,4-bis­(tetrapyridyl)­benzene). After 1 s of xenon lamp irradiation,
compound 1 showed a visible color change from the initial
yellowish to dark purple after continuous irradiation. The photoinduced
radical product has an absorption band covering 200–1700 nm,
which is wider than the absorption ranges of silicon and perovskites.
It produced photocurrent when irradiated with a xenon lamp or a laser
(355, 532, or 808 nm). The on/off ratio of the current (Iirr/Idark) can be as high
as 300 times under the irradiation of the 808 nm laser with a power
of 1.9 W cm–2. In addition, under the 808 nm light
source, the on/off ratio of 1B is 35 times that of 1A.