The Aggregation Regularity Effect of Multiarylpyrroles on Their Near-Infrared Aggregation-Enhanced Emission Property

Two Key Descriptors for Designing Second Near-Infrared Dyes and Experimental Validation

Second near-infrared (NIR-II) optical imaging technology has emerged as a powerful tool for diagnostic and image-guided surgery due to its higher imaging contrast. However, a general strategy for efficiently designing NIR-II organic molecules is still lacking, because NIR-II dyes are usually difficult to synthesize, which has impeded the rapid development of NIR-II bioprobes. Herein, based on the theoretical calculations on 62 multiaryl-pyrrole (MAP) systems with spectra ranging from the visible to the NIR-II region, a continuous red shift of the spectra toward the NIR-II region could be achieved by adjusting the type and site of substituents on the MAPs. Two descriptors (ΔEgs and μgs) were identified as exhibiting strong correlations with the maximum absorption/emission wavelengths, and the descriptors could be used to predict the emission spectrum in the NIR-II region only if ΔEgs ≤ 2.5 eV and μgs ≤ 22.55 D. The experimental absorption and emission spectra of ten MAPs fully confirmed the theoretical predictions, and biological imaging in vivo of newly designed MAP23-BBT showed high spatial resolution in the NIR-II region in deep tissue angiography. More importantly, both descriptors of ΔEgs and μgs have shown general applicability to most of the reported donor-acceptor-donor-type non-MAP NIR-II dyes. These results have broad implications for the efficient design of NIR-II dyes.

Investigation of Mechanochromic Luminescence of Pyrene-based Aggregation-Induced Emission Luminogens: Correlation between Molecular Packing and Luminescence Behavior

To better understand the correlation between molecular structure and optical properties such as aggregation-induced emission (AIE) and mechanochromic luminescence (MCL) emission, two new pyrene-based derivatives with substitutions at the 4- and 5-positions (1HH) and at the 4-, 5-, 9-, and 10-positions (2HH) were designed and synthesized. Cyano groups were introduced at the periphery of the synthesized compounds (1HCN, 1OCN, 1BCN, 2HCN, 2OCN, and 2BCN) to investigate the influence of these groups on the emission properties of the pyrene derivatives both in solution and in the solid state. The fluorescence emission performance of these compounds in water/acetone mixtures was simultaneously studied, revealing outstanding aggregation-induced emission properties. The typical shift in emission maxima to higher values was attributed to J-aggregate formation in the aggregate state. Careful investigation of the crystal structures demonstrated abundant and intense intermolecular interactions, such as C-H…π and C-H…N hydrogen bonds, contributing to the remarkable mechanochromic luminescence performance of these compounds. The MCL properties of all the compounds were investigated using powder X-ray diffraction, and the remarkable mechanochromic properties were attributed to J-aggregate phenomena in the solid state. These results provide valuable insights into the structure-property relationship of organic MCL materials, guiding the design of efficient organic MCL materials.

Hypochlorite Detection by Fluorescent Sensors Bearing Long Alkyl Chains: The Role of Chain Length in Sensing Properties

Three pyridinium derivatives bearing alkyl chains of different lengths (C1, C8, and C18) that show aggregation-enhanced emission were synthesized. These compounds can be used to detect ClO- ion as the reaction releases the fluorescent core with an increase in emission intensity and change in absorption wavelength. The lowest detection limit of TPA-Pyr-18C was 6.04 μM. The length of the alkyl chain and resulting lipophilicity allowed the targeting of different subcellular structures. TPA-Pyr-18C could be used for staining yolk lipids in zebrafish.

An acceptor-shielding strategy of photosensitizers for enhancing the generation efficiency of type I reactive oxygen species and the related photodynamic immunotherapy

Developing efficient photosensitizers (PSs) that can generate type I reactive oxygen species (ROS) under illumination is considered an effective way to improve photodynamic therapy (PDT) outcomes due to the hypoxic nature of the tumor environment, but also is very challenging. Herein, a new PS of the multiarylpyrrole (MAP) derivative with a typical donor-acceptor structure was synthesized to efficiently generate type I ROS by using an acceptor-shielding strategy in their aggregated state. The enhanced generation mechanism of type I ROS originated from its ultralong triplet lifetime and the narrow singlet-triplet energy gap of the MAP. More importantly, type I ROS can transform protumoral M2 macrophages (M2) into antitumoral M1 macrophages (M1), which showed synergistic immunotherapy in in vivo experiments. Therefore, introducing shielding groups into acceptors provides general guidance for developing efficient PSs in the aggregation state for clinical PDT.

Boosting the photodynamic therapy of near-infrared AIE-active photosensitizers by precise manipulation of the molecular structure and aggregate-state packing

Organic functional materials have emerged as a promising class of emissive materials with potential application in cancer phototheranostics, whose molecular structures and solid-state packing in the microenvironment play an important role in reactive oxygen species (ROS) generation and the photodynamic therapy (PDT) effect. Clarifying the guidelines to precisely modulate PDT performance from molecular and aggregate levels is desired but remains challenging. In this work, two compounds, TCP-PF6 and TTCP-PF6, with similar skeletons are strategically synthesized, in which a thiophene segment is ingeniously introduced into the molecular backbone of TCP-PF6 to adjust the intrinsic molecular characteristics and packing in the aggregate state. The experimental and theoretical results demonstrate that TTCP-PF6 can form tight packing mode in comparison with TCP-PF6, resulting in efficient cell imaging and enhanced ROS generation ability in vitro and in vivo. The promising features make TTCP-PF6 a superior photosensitizer for PDT treatment against cancer cells by targeting mitochondria. These findings can provide a feasible molecular design for modulating the biological activity and developing photosensitizers with high ROS generation and PDT effect.

Carbodiimide-Driven Dimerization and Self-Assembly of Artificial, Ribose-Based Amphiphiles

The aqueous self-assembly of amphiphiles into aggregates such as micelles and vesicles has been widely investigated over the past decades with applications ranging from materials science to drug delivery. The combination of characteristic properties of nucleic acids and amphiphiles is of substantial interest to mimic biological self-organization and compartmentalization. Herein, we present ribose- and ribonucleotide-based amphiphiles and investigate their self-assembly as well as their fundamental reactivity. We found that various types of aggregates are formed, ranging in size from nanometers to micrometers and all amphiphiles exhibit aggregation-induced emission (AIE) in solution as well as in the solid state. We also observed that the addition of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) leads to rapid and selective dimerization of the amphiphiles into pyrophosphates, which decreases the critical aggregation concentration (CAC) by a factor of 25 when compared to the monomers. Since the propensity for amphiphile dimerization is correlated with their tendency to self-assemble, our results may be relevant for the formation of rudimentary compartments under prebiotic conditions.