Hydrogen‐Bond Network‐Directed Controllable Assembly of Stable Cyanine J‐Aggregates for Long‐Term and High‐Contrast In Vivo Imaging

Optical probes based on near-infrared region (NIR) small-molecule dyes have emerged as an indispensable tool for contemporary in vivo biomedical research. Nevertheless, the majority of the reported NIR small-molecule probes are plagued by issues such as poor stability, short excitation wavelength, and inadequate lesion retention ability, all of which significantly hinder accuracy in vivo imaging. Herein, we introduce a strategy to construct ultra-stable and optically controllable J-aggregated cyanine (JCy) with rapid in vivo self-assembly ability by incorporating carboxyl groups and adjusting the alkyl chain length of classical heptamethine cyanine dye. Single-crystal x-ray diffraction analysis reveals that the strong hydrogen bonds formed by carboxyl groups enable JCy dyes to assemble into Z-shaped dimers and the dimers interlocking "linear supramolecular arrays (LSA)" within the crystal. These LSAs then undergo a tight and ordered J-aggregation through the electrostatic interactions, C─H⋯O hydrogen bonds and π-π interactions. This unique J-aggregation mechanism confers JCy dyes with carrier-independent in vivo self-assembly and superior stability. As a proof-of-concept, we selected JCy-Bu, which exhibits low concentration dependence, remarkable resistance to protein interference, and outstanding photochemical stability, for in vivo biological study, and have achieved long-term, high-contrast in situ imaging of mouse gastric and tumor tissues.