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Issue 30, 2019
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Unusual triplet–triplet annihilation in a 3D copper(i) chloride coordination polymer

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Abstract

A new coordination polymer (CP) defined as [Cu2Cl2(EtS(CH2)4SEt)4]n (CP2) was prepared by reacting EtS(CH2)4SEt with CuCl in acetonitrile in a 1 : 2 stoichiometric ratio. The X-ray structure reveals formation of non-porous 3D material composed of parallel 2D-[Cu2Cl2S2]n layers of Cl-bridged Cu2(μ-Cl)2 rhomboids assembled by EtS(CH2)4SEt ligands. A weak triplet emission (Φe < 0.0001) is observed in the 400–500 nm range with τe of 0.93 (298 K) and 3.5 ns (77 K) as major components. CP2 is the only 2nd example of emissive thioether/CuCl-containing material and combined DFT/TDDFT computations suggest the presence of lowest energy M/XLCT excited states. Upon increasing the photon flux (i.e. laser power), a triplet–triplet annihilation (TTA) is induced with quenching time constants of 72 ps (kQ = 1.3 × 1010 s−1) and 1.0 ns (kQ = 7.1 × 108 s−1) at 298 and 77 K, respectively, proceeding through an excitation energy migration operating via a Dexter process. Two distinct (Io)1/2 (Io = laser power) dependences of the emission intensity are depicted, indicating saturation as the observed emission increases with the excitation flux. These findings differ from that previously reported isomorphous CP [Cu2Br2(μ-EtS(CH2)4SEt)4]n (CP1), which exhibits no TTA behaviour at 77 K, and only one (laser power)2 dependence at 298 K. The ∼18-fold increase in kQ upon warming CP2 from 77 to 298 K indicates a temperature-aided TTA process. The significant difference between the presence (slower, CP2) and absence (CP1) of TTA at 77 K is explained by the larger unit cell contraction of the former upon cooling. This is noticeable by the larger change in inter-rhomboid Cu⋯Cu separation for CP2.

Graphical abstract: Unusual triplet–triplet annihilation in a 3D copper(i) chloride coordination polymer

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Supplementary files

Article information


Submitted
21 May 2019
Accepted
09 Jul 2019
First published
09 Jul 2019

Phys. Chem. Chem. Phys., 2019,21, 16538-16548
Article type
Paper

Unusual triplet–triplet annihilation in a 3D copper(I) chloride coordination polymer

A. Schlachter, A. Bonnot, D. Fortin, P. Karsenti, M. Knorr and P. D. Harvey, Phys. Chem. Chem. Phys., 2019, 21, 16538
DOI: 10.1039/C9CP02891A

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