Issue 18, 2025

[2 + 2] Photocyclization converts thermally induced spin crossover effect into “hidden hysteresis” one

Abstract

The light induced [2 + 2] cyclization of the flexible coumarin-based ligand (L) converts the spin crossover active HS1 ⇆ LS1 mononuclear system [Fe(L)6](BF4)2·4CH3CN (1) into the high spin 1D coordination polymer (2). The contribution of the resulting high spin form HS2 is directly related to the degree of photoconversion and, at the same time, practically does not affect the properties of the remaining thermally active spin crossover centers (HS1). The origin of such a fundamental change in properties is an appearance of strain caused by ligand dimerization, which acts directly on the metal chromophores and is transmitted to the crystal lattice. The spin state of 2 can be changed by applying pressure as well as by light irradiation revealing a “hidden hysteresis” phenomenon (Appl. Phys. Lett., 2008, 93, 21906), referring to the appearance of the low spin state not accessible through thermal activation but through reversed-LIESST. A unique feature of 2 is the feasibility to attain any steady state within the hidden hysteresis region by combination of perturbations triggered by changes in temperature and light (808 nm HS2 → LS2 and 532 nm LS2 → HS2). Such states are stable within a time scale of several hours.

Graphical abstract: [2 + 2] Photocyclization converts thermally induced spin crossover effect into “hidden hysteresis” one

Supplementary files

Article information

Article type
Edge Article
Submitted
20 Aug 2024
Accepted
24 Mar 2025
First published
25 Mar 2025
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2025,16, 7884-7893

[2 + 2] Photocyclization converts thermally induced spin crossover effect into “hidden hysteresis” one

M. Kaźmierczak, M. Weselski, M. Siczek, J. A. Wolny, V. Schünemann and R. Bronisz, Chem. Sci., 2025, 16, 7884 DOI: 10.1039/D4SC05587J

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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