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Shortwave infrared luminescent Pt-nanowires: mechanistic study of emission in solution and solid state

Abstract

Several complexes of “PtL2” composition containing two cyanoxime ani-ons – 2-oximino-2-cyano-N-piperidineacetamide (PiPCO-) and 2-oximino-2-cyano-N-morpholylacetamide (MCO-) have been obtained and characterized both in solutions and in solid state. Complexes exist as two distinct polymorphs: monomeric yellow complexes, and dark-green [PtL2]n 1D polymers, while for the MCO- anion a red, solvent containing dimeric [Pt(MCO)2xDMSO]2 complex also has been isolated. The interconversion of polymorphs was investigated. The monomeric PtL2 units are arranged into the anisotropic extended solid [PtL2]n polymers with the help of Pt---Pt metallophilic interactions. Crystal structures of monomeric PtL2 (L= PiP-CO-, MCO-) and red dimeric [Pt(MCO)2xDMSO]2 complexes were deter-mined and revealed the cis-arrangement of cyanoxime anions. The Pt-Pt distance in the “head-to-tail” red dimer was found to be 3.133 Å. The structure of polymeric [Pt(PiPCO)2]n compound was elucidated using the EXAFS method and evidenced the formation of the Pt-wire with ~3.15 Å intermetallic separations. The EPR spectra of both 1D polymers at varia-ble temperatures indicate the absence of Pt(III) species. Both pure dark-green [PtL2]n polymers showed considerable room temperature electrical conductivity of 20-30 S/cm, which evidences the formation of mixed va-lence Pt(II)/Pt(IV) system. We discovered that these 1D polymeric [PtL2]n complexes show an intense NIR fluorescence beyond 1000 nm, while yellow monomeric PtL2 complexes are not emissive at all. The room tem-perature excitation spectra of 1D polymeric [PtL2]n complexes demon-strated their strong emission beyond 1000 nm regardless of the used excitation wavelength between 350 and 800 nm, which is typical of sys-tems with delocalized charge carriers. For the first time the formation of mixed valence “metal wire” assembled by metallophilic interactions is directly linked both with an intense fluorescence in the NIR region of spectrum and the electrical conductivity. The effect of concentration of [PtL2]n complexes dispersed in the dielectric salt matrix on the photolumi-nescence wavelength and intensity was investigated. Both polymers show a remarkably high for this region of spectrum quantum yield reach-ing ~2%. Variable temperature emission of polymeric [PtL2]n in the -190 - +60oC range was studied as well.

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Publication details

The article was received on 26 Jun 2017, accepted on 06 Sep 2017 and first published on 06 Sep 2017


Article type: Paper
DOI: 10.1039/C7DT02317K
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Shortwave infrared luminescent Pt-nanowires: mechanistic study of emission in solution and solid state

    C. Cheadle, J. Ratcliff, M. Y. Berezin, V. Pal'shin, V. Nemykin and N. Gerasimchuk, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT02317K

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