Solvatochromic Near-Infrared Aggregation-Induced Emission-Active Acrylonitriles by Acceptor Modulation for Low-Power Stimulated Emission Depletion Nanoscopy

Abstract

Stimulated emission depletion (STED) nanoscopy has broadened our horizons to unravel mysterious functions of cellular structures on an unparalleled nanometer scale. Nevertheless, an intense depletion laser power is a general prerequisite for STED super-resolution imaging with a satisfactory resolution, inevitably leading to severe photobleaching of fluorophores, irreparable photodamage to biosamples, and impaired imaging quality. Herein, by modulating distinct acceptor units, a series of donor−acceptor−acceptor structured fluorescent acrylonitriles featured with aggregation-induced emission (AIE) for STED super-resolution imaging at a low depletion power were systematically developed. These AIE luminogens (AIEgens) exhibited tunable near-infrared emissions (650−733 nm) and high fluorescence quantum yields (QYs of up to 26.8%) in the solid state, significant Stokes shifts, and large twophoton absorption cross-sections. They also exhibited a typical solvatochromic effect and ultrahigh QYs of up to 98.4% in low-polarity solvents. Furthermore, these lipophilic solvatochromic acrylonitriles specifically lit up lipid droplets (LDs) with exceptionally high photostability in a washfree manner. By taking TPA-BT-ANBI as an example, the STED super-resolution imaging of LDs with excellent resolution of 62 and 80 nm for cytosolic and nuclear LDs, respectively, at a low saturation depletion power of 0.83 MW/cm 2 and extended time-lapse imaging of LD dynamics was achieved. Subsequent use of TPA-BT-ANBI for the optical discrimination of fatty liver tissues and twophoton deep-tissue imaging was also demonstrated. This study opens new avenues for versatile photostable materials at low depletion powers for target-specific STED super-resolution imaging.

Molecular and Aggregate Synergistic Engineering of Aggregation-Induced Emission Luminogens to Manipulate Optical/Electronic Properties for Efficient and Diversified Functions

“…Two-photon fluorescence microscopy (2PFM) is an effective strategy to translate the excitation of probes from the short-wavelength region to near-infrared I and even II windows (NIR-I, 650–900 nm, NIR-II, 900–1880 nm). − By contrast, NIR-II two-photon excitation could provide deeper penetration depth owing to much lower scattering from the biotissues. , Additionally, compared to confocal microscopy, the spatial localization of two-photon excitation processes would also endow 2PFM with high signal-to-background ratio (SBR), sectioning ability, and less tissue damage to the out-of-focus areas . Thus, 2PFM is a promising powerful tool for observing the highly integrated brain structure in vivo with deep imaging depth and high resolution.…”

Cationic tetraphenylethylene-based AIE-active acrylonitriles: investigating the regioisomeric effect, mechanochromism, and wash-free bioimaging

“…Recently, acrylonitriles have emerged as a new building block to develop donor-acceptor-based AIEgens, because of their facile synthesis and easy purification. [50][51][52][53] We anticipated that conjugation of TPE at ortho/meta/para positions with the basic acrylonitrile skeleton could lead to new AIE-active regioisomers, which has not been explored so far.…”

Effects of Halogenation on Quinoline‐Malononitrile‐based AIEgens: Photophysical Properties Investigation and Wash‐Free Imaging

“…[7,[10][11][12] The mechanism of restriction of intramolecular motion (RIM) proposed by Tang et al has been widely accepted to explain the unique fluorescence of AIEgens. [7] Guided by the RIM mechanism, scientists around the world have made great efforts to develop various kinds of AIEgens, including siloles, [13][14][15] tetraphenylethylenes, [16][17][18] tetraphenylpyrazines, [19][20][21] acrylonitriles, [22][23][24] and metal complexes, [25][26][27] for molecule detection, bioimaging, disease diagnosis, and therapy. [28][29][30][31][32][33][34] Among these, the quinolinemalononitrile core developed by Zhu and co-workers has become an attractive building block for constructing multiple functional AIEgens, because of their facile synthesis and bright solid-state fluorescence.…”