Molecular materials that exhibit stimuli-responsive bistability are promising candidates for the development of molecular switches and sensors. We herein report on the coexistence of a wide thermal hysteretic spin crossover (SCO) effect and a thermally inducible metastable high-spin state at low temperatures achieved with the two new complexes [FeII(Lnpdtz)2(NCX)2] (X = S; Se), with Lnpdtz being (2-naphthyl-5-pyridyl-1,2,4-thiadiazole) and X = S (1) and Se (2). Pronounced π–π-stacking of the aromatic side residues of the ligands enables strong intermolecular interactions, leading to abrupt SCO properties and broad magnetic hysteresis of 10 K for X = S and 58 K for X = Se. In this paper, we also present the pressure-induced spin-state switching around 0.8 GPa. A pronounced thermally induced excited spin state trapping (TIESST effect) is observed for the highly cooperative SCO compounds, which was experimentally followed by low-temperature single crystal structure analysis (20 K) and temperature-dependent Mössbauer spectroscopy.

The design and development of photoinitiating systems applicable to UV or even visible light delivered from light‐emitting diodes (LEDs) has been attracting increasing attention due to their great potential applications in various fields. Compared to the strategy of synthesizing novel compounds, the exploration of existing chemicals with interesting photochemical/photophysical properties for their usage as photoinitiators is more appealing and easily commercialized. Nevertheless, a number of compounds such as monoamino‐substituted anthraquinone derivatives, which are intensively investigated for their photophysical and photochemical properties, have seldom been studied for their roles as photoinitiators under LED irradiation. Herein, three monoamino‐substituted anthraquinone derivatives, that is, 1‐aminoanthraquinone, 1‐(methylamino)anthraquinone and 1‐(benzamido)anthraquinone, are studied for their potential as photoinitiators. The photoinitiation mechanism of these monoamino‐substituted anthraquinone derivatives, when combined with iodonium salt, is first clarified using computational quantum chemistry, fluorescence, steady‐state photolysis, and electron spin resonance spin‐trapping techniques. Then, their photoinitiation ability for the cationic photopolymerization of epoxide and divinyl ether monomers is also investigated.

We report the multistep synthesis of a thiadiazole based ligand (L OMe-Nap ) with a methoxy substituent in the sixposition of the naphthalene ring, along with the corresponding iron(II) [Fe II (L OMe-Nap ) 2 (NCE) 2 ] 1−3 (E = S, Se, and BH 3 ) complexes. We also report the synthesis of the [Fe II (L Nap ) 2 (NCBH 3 ) 2 ] (4) complex with the previously reported L Nap ligand. The complexes obtained were characterized by single crystal X-ray crystallography and SQUID magnetometry in all four cases (1−4). Complex 1 shows a weak thermally induced excited spin state trapping (TIESST) effect up to about 60 K. The effects of the methoxy ligand substituent in altering the noncovalent intramolecular π−π interaction are discussed, as well as the tuning of the switching temperature (T 1/2 ) by the choice of NCE. The S < Se < BH 3 series is established in both families of compounds.

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