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

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  • ReceivedSep 17, 2020
  • AcceptedOct 15, 2020
  • PublishedJan 18, 2021


Producing ultra-stabilized radicals via light irradiation has raised considerable concern but remains a tremendous challenge in functional materials. Herein, optically actuating ultra-stable radicals are discovered in a sterically encumbered and large π-conjugated tri(4-pyridyl)-1,3,5-triazine (TPT) ligands constructed photochromic compound Cu3(H-HEDP)2TPT2·2H2O (QDU-12; HEDP=hydroxyethylidene diphosphonate). The photogeneration of TPT radicals is the photoactive behavior of electron transfer from HEDP motifs to TPT units. The ultra-long-lived radicals are contributed from strong interchain π-π interactions between the large π-conjugated TPT components, with the radical lifetime maintained for about 18 months under ambient conditions. Moreover, the antiferromagnetic couplings between TPT radicals and Cu2+ ions plummeted the demagnetization to 35% of its original state after light irradiation, showing the largest room temperature photodemagnetization in the current radical-based photochromic materials.

Funded by

the National Natural Science Foundation of China(21901133,22071125,22071126,21571111)

the Key Research and Development Project of Shandong Province(2019GGX102006)


This work was supported by the National Natural Science Foundation of China (21901133, 22071125, 22071126, 21571111) and the Key Research and Development Project of Shandong Province (2019GGX102006). We thank for Dr Jian-Hua Qin (Luoyang Normal University, China) for the SCXRD data refinements.

Interest statement

The authors declare no conflict of interest.

Contributions statement

These authors contributed equally to this work


The supporting information is available online at http://chem.scichina.com and http://link.springer.com/journal/11426. The supporting materials are published as submitted, without typesetting or editing. The responsibility for scientific accuracy and content remains entirely with the authors.


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  • Figure 1

    The structure of QDU-12. (a) The asymmetric unit; (b) the interchain π-π interactions between the TPT ligands. H atoms and lattice waters are omitted for clarity. Color codes: Cu turquoise; P pink; C gray 40%; O red; N blue (color online).

  • Figure 2

    (a) The photochromic phenomenon of powder samples for QDU-12; (b) time-dependent UV-Vis diffuse-reflectance spectra of QDU-12 upon light irradiation; (c) the plot of relative intensity of time-dependent UV-Vis spectra upon light irradiation at 480 nm. The red solid line presented the fitted curve; (d) solid state ESR spectra of QDU-12 and QDU-12A at room temperature (color online).

  • Figure 3

    The Cu 2p (a), N 1s (b), O 1s (c) and C 1s (d) of XPS core-level spectra for QDU-12 and QDU-12A (color online).

  • Figure 4

    The calculated spatial distributions of LUMO and HOMO of QDU-12 at the B3LYP/6-311G(d) level (color online).

  • Figure 5

    (a) UV-Vis diffuse-reflectance spectra for QDU-12A in dark at different time; (b) the decayed UV-Vis diffuse-reflectance spectra for QDU-12A at an interval of 30 min. The inserted curve represents the relaxation kinetics of reflective intensity at 560 nm (converted into absorbance) in normalized values (t=0 min, converted fraction=1) for QDU-12A in the dark at room temperature, and the red solid line presented the stretched-exponential fitted curve (color online).

  • Figure 6

    Interchain π-π interactions between terminal TPT ligands among the adjacent double chains for QDU-12 and QDU-12A (color online).

  • Figure 7

    Temperature-dependent susceptibilities of QDU-12 and QDU-12A under a dc magnetic field of 1000 Oe (color online).