David Harding (@groupharding.bsky.social)

Really pleased to see this paper published in Inorg Chem @pubs.acs.org with my good friend Prof Pichaya from VISTEC, with help from NZ and Japan. A Stokes shift of 15,000 cm-1 was not at all what we were expecting with these compounds! pubs.acs.org/doi/10.1021/...

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Near-Infrared Luminescence from Transparent Thin Films of Copper(I) Thiocyanate Modified with 2-Mercaptobenzothiazole via Excited-State Symmetry Breaking Near-infrared (NIR) emission in molecular materials is typically achieved by narrowing the band gap through extended π-conjugation or heavy-atom substitution. Here, we report an unconventional route─excited-state symmetry breaking─that enables NIR emission while preserving a wide band gap. Copper(I) thiocyanate (CuSCN), a transparent semiconductor with optical activity normally observed only in the ultraviolet region, forms a dimeric complex with 2-mercaptobenzothiazole (MBTz). In thin films, CuSCN-MBTz complex exhibits NIR photoluminescence at 800 nm, while retaining a large optical gap (>3 eV), resulting in a transparent NIR-emissive material with a large Stokes shift of ∼15,000 cm–1. Structural and spectroscopic analyses reveal that, unlike the rigid crystalline phase, the film state allows molecular reorganization of Cu2(SCN)2(MBTz)4 dimers, which induces symmetry breaking and lowers the energy of the emissive state without reducing the band gap, in contrast to typical Cu(I) emitters. This work provides a new photophysical mechanism for generating long-wavelength emission from wide-band gap, earth-abundant Cu(I) systems and widens the functional scope of CuSCN materials. https://pubs.acs.org/doi/10.1021/acs.inorgchem.5c05480