Directed self-assembly of viologen-based 2D semiconductors with intrinsic UV–SWIR photoresponse after photo/thermo activation

Abstract

Extending photoresponse ranges of semiconductors to the entire ultraviolet-visible (UV)-shortwave near-infrared (SWIR) region (ca. 200-3000 nm) is highly desirable to reduce complexity and cost of photodetectors or to promote power conversion efficiency of solar cells. The observed up limit of photoresponse for organic-based semiconductors is about 1800 nm, far from covering the UV-SWIR region. Here we develop a cyanide-bridged layer-directed intercalation approach and obtain a series of two viologen-based 2D semiconductors with multispectral photoresponse. In these compounds, infinitely π-stacked redox-active N-methyl bipyridinium cations with near-planar structures are sandwiched by cyanide-bridged Mn II -Fe III or Zn II -Fe III layers. Radical-π interactions among the infinitely πstacked N-methyl bipyridinium components favor the extension of absorption range. Both semiconductors show light/thermo-induced color change with the formation of stable radicals. They have intrinsic photocurrent response in the range of at least 355-2400 nm, which exceeds all reported values for known single-component organic-based semiconductors.

A Photochromic Zinc–Viologen Framework with a High-Contrast Nonlinear Optical Switchable Behavior

“…Their intensity increases gradually with the duration of irradiation time and nearly reaches an ultimate saturation level after illumination for 25 min. On the basis of previous reports, − the characteristic absorption bands may result from the photogenerated viologen radicals through intra- and/or intermolecular electron transfer, which has indeed been confirmed by EPR studies.…”

Broadband Photoresponsive Bismuth Halide Hybrid Semiconductors Built with π-Stacked Photoactive Polycyclic Viologen

“…Photoinduced electron transfer (PIET) using an electron-transfer photochromic ligand, like viologen, − especially favors postsynthesis, because a radical product may be generated in situ and the limit of stereospace is tiny. As for the second challenge, our group has recently established an effective coordination-directed intercalation self-assembly method; however, this method is still subjected to cyano-bridged systems to date.…”

Optically actuating ultra-stable radicals in a large π-conjugated ligand constructed photochromic complex

“…In this respect, the electron-transfer photochromic complexes undoubtedly can be served as an ideal medium, in which naked-eye detectible color changes are easily observed and relatively stable radicals can be effectively regulated through direct light irradiation. Hitherto, lots of photochromic complexes have been prepared by using the donor-acceptor strategy, exemplified by some inorganicorganic hybrid photochromic frameworks, in which electronrich inorganic motifs like metallophosphates, polyoxomolybdates and halometallates [20][21][22] may offer electrons while electron-deficient organic groups [23][24][25] may be prone to accepting and stabilizing generated radicals. However, it is still a pivotal research challenge for extremely improving the stability of the photogenerated radicals under ambient conditions, which could greatly enhance the catalysis, luminescence and conductivity of the radical-based functional properties.…”