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Molecules 2016, 21(9), 1227;

Molecular-Based Fluorescent Nanoparticles Built from Dedicated Dipolar Thienothiophene Dyes as Ultra-Bright Green to NIR Nanoemitters

Institut des Sciences Moléculaires (UMR 5255 CNRS), Université de Bordeaux, 33400 Talence, France
Author to whom correspondence should be addressed.
Academic Editor: Zhen Cheng
Received: 2 August 2016 / Revised: 2 September 2016 / Accepted: 6 September 2016 / Published: 14 September 2016
(This article belongs to the Special Issue Molecular Imaging Probes)
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Fluorescent Organic Nanoparticles (FONs), prepared by self-aggregation of dedicated dyes in water, represent a promising green alternative to the toxic quantum dots (QDs) for bioimaging purposes. In the present paper, we describe the synthesis and photophysical properties of new dipolar push-pull derivatives built from thieno[3,2-b]thiophene as a π-conjugated bridge that connects a triphenylamine moiety bearing various bulky substituents as electron-releasing moiety to acceptor end-groups of increasing strength (i.e., aldehyde, dicyanovinyl and diethylthiobarbiturate). All dyes display fluorescence properties in chloroform, which shifts from the green to the NIR range depending on the molecular polarization (i.e., strength of the end-groups) as well as a large two-photon absorption (TPA) band response in the biological spectral window (700–1000 nm). The TPA bands show a bathochromic shift and hyperchromic effect with increasing polarization of the dyes with maximum TPA cross-section reaching 2000 GM for small size chromophore. All dyes are found to form stable and deeply colored nanoparticles (20–45 nm in diameter) upon nanoprecipitation in water. Although their fluorescence is strongly reduced upon aggregation, all nanoparticles show large one-photon (up to 108 M−1·cm−1 in the visible region) and two-photon (up to 106 GM in the NIR) brightness. Interestingly, both linear and non-linear optical properties are significantly affected by interchromophoric interactions, which are promoted by the molecular confinement and modulated by both the dipolar strength and the presence of the bulky groups. Finally, we exploited the photophysical properties of the FONs to design optimized core-shell nanoparticles built from a pair of complementary dipolar dyes that promotes an efficient core-to-shell FRET process. The resulting molecular-based core-shell nanoparticles combine large two-photon absorption and enhanced emission both located in the NIR spectral region, thanks to a major amplification (by a factor of 20) of the core fluorescence quantum yield. These novel nanoparticles, which combine huge one-and two-photon brightness, hold major promise for in vivo optical bioimaging. View Full-Text
Keywords: fluorescence; thienothiophene; nanoparticles; dipolar chromophores; two-photon absorption fluorescence; thienothiophene; nanoparticles; dipolar chromophores; two-photon absorption

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Mastrodonato, C.; Pagano, P.; Daniel, J.; Vaultier, M.; Blanchard-Desce, M. Molecular-Based Fluorescent Nanoparticles Built from Dedicated Dipolar Thienothiophene Dyes as Ultra-Bright Green to NIR Nanoemitters. Molecules 2016, 21, 1227.

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