ACQ‐to‐AIE Transformation: Tuning Molecular Packing by Regioisomerization for Two‐Photon NIR Bioimaging

Abstract

The traditional design strategies for highly bright solid‐state luminescent materials rely on weakening the intermolecular π–π interactions, which may limit diversity when developing new materials. Herein, we propose a strategy of tuning the molecular packing mode by regioisomerization to regulate the solid‐state fluorescence. TBP‐e‐TPA with a molecular rotor in the end position of a planar core adopts a long‐range cofacial packing mode, which in the solid state is almost non‐emissive. By shifting molecular rotors to the bay position, the resultant TBP‐b‐TPA possesses a discrete cross packing mode, giving a quantum yield of 15.6±0.2 %. These results demonstrate the relationship between the solid‐state fluorescence efficiency and the molecule's packing mode. Thanks to the good photophysical properties, TBP‐b‐TPA nanoparticles were used for two‐photon deep brain imaging. This molecular design philosophy provides a new way of designing highly bright solid‐state fluorophores.

Incorporation of Planar Blocks into Twisted Skeletons: Boosting Brightness of Fluorophores for Bioimaging beyond 1500 Nanometer

“…The planar thiophene unit is introduced as both an electron donor and π-conjugation bridge. The role of alkyl chains is of vital importance; it should be grafted to the thiophene unit adjacent to BBTD core to distort the backbone, resulting in AIE properties. ,, The resultant distorted backbone, on the one hand, contributes a high Φ PL in the aggregate or solid state owing to the suppression of intermolecular π–π packing; , on the other hand, it inevitably results in the decrease of absorptivity because of the breakage in the conjugation. As both Φ PL and absorptivity determine the brightness, there is still some room for further promoting the brightness of AIEgens.…”

Molecular Crystal Engineering of Organic Chromophores for NIR-II Fluorescence Quantification of Cerebrovascular Function

“…Large π-conjugated TBP with a planar structure has been proved to perform as a robust electronic acceptor for high electron delocalization and offer a platform for tuning intermolecular π−π interactions. 32 However, the powerful intermolecular interactions easily quench the fluorescence in the aggregated state. To solve this problem, twisted molecular rotor TPA (also electronic donor) was introduced to the bay position TBP unit (Figure 1, left), giving TBP-b-TPA typical AIE properties.…”

“…Recently, a planar electronic acceptor unit dithieno[2,3a:3′,2′-c]benzo[i]phenazine (TBP) has been proved that it can easily form single crystal structures when coupled with electronic donors. 32 However, owing to the relatively weak…”

Twisted Intramolecular Charge Transfer—Aggregation-Induced Emission Fluorogen with Polymer Encapsulation-Enhanced Near-Infrared Emission for Bioimaging

“…[8][9][10][11][12][13] Water-soluble AIE luminogens (AIEgens) have attracted much attention because they are beneficial for biological probing and imaging. In general, encapsulation media, such as inorganic substrates of silica, 14,15 organic substrates of surfactants, [16][17][18] and amphiphilic copolymers, [19][20][21] are used as matrices to improve the water solubility of lipophilic AIE dyes. AIE dyes encapsulated by polymer matrices are widely used in FMI due to their good biocompatibility, photostability, and water solubility; polymer-encapsulated AIEgens with a far-red/nearinfrared (NIR) wavelength range are especially attractive because of their superior performance due to high imaging penetration depth and enhanced signal-to-noise ratio.…”