Robust luminescent dyes with efficient two-photon fluorescence are highly desirable for biological imaging applications, but those suitable for organic dots fabrication are still rare because of aggregation-caused quenching. In this work, a red fluorescent silole, 2,5-bis[5-(dimesitylboranyl)thiophen-2-yl]-1-methyl-1,3,4-triphenylsilole ((MesB)2 DTTPS), is synthesized and characterized. (MesB)2 DTTPS exhibits enhanced fluorescence efficiency in nanoaggregates, indicative of aggregation-enhanced emission (AEE). The organic dots fabricated by encapsulating (MesB)2 DTTPS within lipid-PEG show red fluorescence peaking at 598 nm and a high fluorescence quantum yield of 32%. Upon excitation at 820 nm, the dots show a large two-photon absorption cross section of 3.43 × 10(5) GM, which yields a two-photon action cross section of 1.09 × 10(5) GM. These (MesB)2 DTTPS dots show good biocompatibility and are successfully applied to one-photon and two-photon fluorescence imaging of MCF-7 cells and two-photon in vivo visualization of the blood vascular of mouse muscle in a high-contrast and noninvasive manner. Moreover, the 3D blood vasculature located at the mouse ear skin with a depth of over 100 μm can also be visualized clearly, providing the spatiotemporal information about the whole blood vascular network.
BODIPY (4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene) is an emissive chromophore in solutions but suffers from fluorescence quenching when aggregated due to its flat molecular conformation and small Stokes shift. To create aggregate‐state emissive BODIPY luminogens, tetraphenylethene (TPE), which is a popular luminogen with intriguing aggregation‐induced emission (AIE) characteristic, is introduced as periphery to a methylated BODIPY core. Three TPE‐BODIPY adducts are synthesized and characterized, and their photophysical properties and electronic structures are investigated. The incorporation of AIE‐active TPE units alleviates aggregation‐caused quenching of BODIPY core, furnishing emissive nanoparticles based on TPE‐BODIPY adducts. Significantly, the two‐photon absorption (TPA) and two‐photon excited fluorescence (TPEF) properties are improved as more TPE units are attached. The luminogens with 3TPE units (3TPE‐BODIPY) shows the strongest TPA and TPEF in the wavelength range of 750–830 nm, with cross‐section values of 264 and 116 GM at 810 nm, respectively. Red emissive nanoparticles with a Stokes shift of 60 nm and a fluorescence quantum yield of 16% are attained by encapsulating 3TPE‐BODIPY with 1,2‐sistearoyl‐sn‐glycero‐3‐phosphoethanolamine‐N‐[methoxy(polyethylene glycol)‐2000]. The nanoparticles are biocompatible and function well in TPEF cellular imaging and mouse brain blood vascular visualization.
In this work the two-photon activity of nanoparticles obtained from a fluorene monomer (M1) and its cross-conjugated polymer (P1) is reported. Aqueous suspensions of M1 and P1 nanoparticles prepared through the reprecipitation method exhibited maximum two-photon absorption (TPA) cross-sections of 84 and 9860 GM (1 GM = 10(-50) cm(4) s) at 740 nm, respectively, and a fluorescence quantum yield of ~1. Such a two-photon activity was practically equal with respect to that for molecular solutions of M1 and P1. These materials were then successfully encapsulated into silica nanoparticles to provide bio-compatibly. A lung cancer cell line (A549) and a human cervical cancer cell line (HeLa cells) were incubated with our fluorescent silica nanoparticles to carry out two-photon imaging. By means of these studies we demonstrate that optimized nonlinear optical polymers loaded in silica nanoparticles can be used as efficient probes with low cytotoxicity and good photostability for two-photon fluorescence microscopy. To the best of our knowledge, studies concerning polymer-doped silica nanoparticles exhibiting large two-photon activity have not been reported in the literature.
Integration of tetraphenylethene featuring aggregation‐induced emission and a conventional chromophore furnishes efficient red luminescent materials. As discussed on page 481, Zujin Zhao and co‐workers fabricate biocompatible nanoparicles that show great potential for use in two‐photon excited fluorescence cellular imaging and three‐dimensional vascular visualization.
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