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Cooperative phenomenon of vapochromism and proton conduction of luminescent Pt(II) complexes for the visualisation of proton conductivity

Abstract

The luminescent and proton conductive Pt(II) complex [PtCl(tpy-o-py)]Cl and its HCl adduct [PtCl(tpy-o-pyH)]Cl2 (o-Pt and o-Pt·HCl, respectively; tpy-o-py = 2,2′: 6′,2′′-terpyridine-6′,2′′′-pyridine) were synthesised and their crystal structures, vapochromic behaviour, and proton conduction investigated and compared to those of the para isomers [PtCl(tpy-p-py)]Cl and [PtCl(tpy-p-pyH)]Cl2 (p-Pt and p-Pt·HCl, respectively; tpy-p-py = 2,2′: 6′,2′′-terpyridine-4′,4′′′-pyridine). X-ray structure analysis revealed that intermolecular metallophilic (Pt···Pt) interaction was negligible in o-Pt but effective in o-Pt·HCl. Reversible transformation between o-Pt and o-Pt·HCl coupled with significant colour and luminescence changes was achieved by four different external stimuli, namely, exposure of o-Pt to humid HCl gas to form o-Pt·HCl, heating, exposure to MeOH vapour, and finally drying in air to regenerate the original o-Pt. The intraligand π-π* orange emission observed for o-Pt exhibited negligible dependence on the relative humidity (RH). Conversely, o-Pt·HCl exhibited red metal-metal-to-ligand charge-transfer (MMLCT) phosphorescence at 725 nm, originating from effective intermolecular Pt-Pt interaction, and interesting vapochromic behaviour that was dependent on the RH. Notably, o-Pt·HCl presented higher conductivity than the p-Pt·HCl isomer at RH <80%. This trend was reversed at RH values >80%, probably owing to the second water-adsorption-induced transformation of p-Pt·HCl. The cooperative phenomenon between the proton conduction and vapochromic behaviour observed for both o-Pt·HCl and p-Pt·HCl should allow the visualisation of the proton-conducting pathway, without the need for a bulk electrode, via the absorption and emission colours at both the macroscopic and microscopic levels.

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Supplementary files

Article information


Submitted
06 Jan 2020
Accepted
14 Apr 2020
First published
14 Apr 2020

Faraday Discuss., 2020, Accepted Manuscript
Article type
Paper

Cooperative phenomenon of vapochromism and proton conduction of luminescent Pt(II) complexes for the visualisation of proton conductivity

A. Kobayashi, S. Imada, D. Wang, Y. Nagao, M. Yoshida and M. Kato, Faraday Discuss., 2020, Accepted Manuscript , DOI: 10.1039/D0FD00001A

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