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Open AccessArticle

On the Nature of Luminescence Thermochromism of Multinuclear Copper(I) Benzoate Complexes in the Crystalline State

1
Department of Chemistry, University of Warsaw, Żwirki i Wigury 101, 02-089 Warsaw, Poland
2
Department of Chemistry, University of Wrocław, Joliot-Curie 14, 50-383 Wrocław, Poland
3
Department of Chemistry, Oakland University, 146 Library Drive, Rochester, MI 48309-4479, USA
*
Author to whom correspondence should be addressed.
Crystals 2019, 9(1), 36; https://doi.org/10.3390/cryst9010036
Received: 30 November 2018 / Revised: 3 January 2019 / Accepted: 6 January 2019 / Published: 12 January 2019
(This article belongs to the Special Issue Photocrystallography and Solid-State Structural Dynamics)
A model luminescent [(PhCO2)4Cu4] (Cu4) complex in the crystalline state was investigated via combined crystallographic and spectroscopic techniques contributed substantially by theoretical modelling. The complex appeared to exhibit luminescence thermochromism, i.e., red phosphorescence at room temperature which changes to green when lowering the temperature to 90 K. The low-energy emissive state was assigned as a cluster-centred triplet, 3CC. The emission from this state predicted in TDDFT (~635 nm) matches the experimental red band observed at 660–715 nm. In contrast, the nature of the high-energy “green” band was less straightforward. The next reached cluster-centred triplet excited state occurred to be energetically close to the experimental value of ~545 nm. The two excited states also exhibit significant metal-to-ligand and ligand-to-metal charge transfer characteristics, especially for solid-state distorted geometries. In both cases the cluster core was expected to become notably contracted when compared to the ground state. Time-resolved photocrystallographic results supported the computationally predicted core contraction upon excitation. Additionally, the differences between the spectroscopic behaviour of the related tetra- and hexanuclear copper(I) complexes, Cu4 and Cu6 (i.e., [(PhCO2)6Cu6]) in the crystalline state were discussed and examined. It appeared that crystal packing may constitute an important factor as far as the lack of luminescence thermochromism in the latter case is concerned. Synopsis: Structure–property relationships characterising a model luminescent [(PhCO2)4Cu4] (Cu4) complex in the crystalline state were investigated via combined crystallographic and spectroscopic techniques contributed by theoretical modelling, and compared with the properties of the related [(PhCO2)6Cu6] (Cu6) complex. View Full-Text
Keywords: cuprophilic interactions; luminescence thermochromism; photocrystalographic studies; solid-state spectroscopy; theoretical calculations; electronic excited states cuprophilic interactions; luminescence thermochromism; photocrystalographic studies; solid-state spectroscopy; theoretical calculations; electronic excited states
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MDPI and ACS Style

Jarzembska, K.N.; Hapka, M.; Kamiński, R.; Bury, W.; Kutniewska, S.E.; Szarejko, D.; Szczęśniak, M.M. On the Nature of Luminescence Thermochromism of Multinuclear Copper(I) Benzoate Complexes in the Crystalline State. Crystals 2019, 9, 36.

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