Hybrids of gold nanoparticles and oligo(p-phenyleneethynylene)s end-functionalized with alkynylruthenium groups: Outstan
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search School of Chemistry, Australian National University, Canberra, ACT 2601, Australia Advanced Materials Engineering and Modelling Group, Wroclaw University of Science and Technology, Wroclaw 50-370, Poland
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 13 April 2020 / Revised: 4 June 2020 / Accepted: 5 June 2020
ABSTRACT Oligo(p-phenyleneethynylene)s (OPEs) end-capped with (alkynyl)bis(diphosphine)ruthenium and thiol/thiolate groups stabilize ca. 2 nm diameter gold nanoparticles (AuNPs). The morphology, elemental composition and stability of the resultant organometallic OPE/AuNP hybrid materials have been defined using a combination of molecular- and nano-material chacterization techniques. The hybrids display long-term stability in solution (more than a month), good solubility in organic solvents, reversible rutheniumcentered oxidation, and transparency beyond 800 nm, and possess very strong nonlinear absorption activity at the first biological window, and unprecedented two-photon absorption activity in the second biological window (σ2 up to 38,000 GM at 1,050 nm).
KEYWORDS gold nanoparticles, inorganic materials, metal alkynyl complexes, nonlinear optics, organometallics
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Introduction
Molecular and nano-materials that display nonlinear absorption (NLA) are attracting attention due to potential or demonstrated applications in optical data storage, imaging, optical limiting, telecommunications, medicine, and 3D-patterning [1–4]. Particular interest has been shown in tailoring materials with high transparency and efficient NLA activity in the near-infrared (NIR) spectral region, because NLA activity in this region will enable devices exploiting NLA to operate at technologicallyimportant wavelengths such as the optical fiber windows (around 1,300 and 1,550 nm) and the second biological window (1,000–1,700 nm) [5]. A range of structural features of materials have been shown to advantageously impact on NLA performance [6–9]. For example, localized surface plasmon resonance (LSPR) at gold nanoparticles (AuNPs) can potentially afford strong NLA due to ultrafast field enhancement at the metal-dielectric interface [10]. Coating AuNPs with sulfur-containing species has afforded two-photon absorption (2PA) activity peaking in the visible and with weaker 2PA maxima extending into the NIR (to 800 nm) [11–14]. Despite these encouraging results, little is known of the wavelength-dependence of 2PA for AuNPs and their hybrids at longer wavelengths, the only report revealing modest 2PA for a captopril-AuNP hybrid (maximal cross-section σ2 = 1,510 GM @ 900 nm; 1 GM = 10−50 cm4·s·photon−1; captopril = (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid) [13]. Oligo(p-phenyleneethynylene)-(OPE-)based entities (rods, dendrimers, etc.) containing ruthenium alkynyl complex moieties Address correspondence to [email protected]
exhibit strong 2PA and record multiphoton absorption (3PA and 4PA) cross-sections extending deep into the NIR [15, 16]. tran
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