Synthesis of fluorescent polycarbonates with highly twisted N,N-bis(dialkylamino)anthracene AIE luminogens in the main chain

Dense and Acidic Organelle-Targeted Visualization in Living Cells: Application of Viscosity-Responsive Fluorescence Utilizing Restricted Access to Minimum Energy Conical Intersection

Cell-imaging methods with functional fluorescent probes are an indispensable technique to evaluate physical parameters in cellular microenvironments. In particular, molecular rotors, which take advantage of the twisted intramolecular charge transfer (TICT) process, have helped evaluate microviscosity. However, the involvement of charge-separated species in the fluorescence process potentially limits the quantitative evaluation of viscosity. Herein, we developed viscosity-responsive fluorescent probes for cell imaging that are not dependent on the TICT process. We synthesized AnP₂-H and AnP₂-OEG, both of which contain 9,10-di(piperazinyl)anthracene, based on 9,10-bis(N,N-dialkylamino)anthracene that adopts a nonflat geometry at minimum energy conical intersection. AnP₂-H and AnP₂-OEG exhibited enhanced fluorescence as the viscosity increased, with sensitivities comparable to those of conventional molecular rotors. In living cell systems, AnP₂-OEG showed low cytotoxicity and, reflecting its viscosity-responsive property, allowed specific visualization of dense and acidic organelles such as lysosomes, secretory granules, and melanosomes under washout-free conditions. These results provide a new direction for developing functional fluorescent probes targeting dense organelles.

Principles of Aggregation-Induced Emission: Design of Deactivation Pathways for Advanced AIEgens and Applications

Twenty years ago, the concept of aggregation-induced emission (AIE) was proposed, and this unique luminescent property has attracted scientific interest ever since. However, AIE denominates only the phenomenon, while the details of its underlying guiding principles remain to be elucidated. This minireview discusses the basic principles of AIE based on our previous mechanistic study of the photophysical behavior of 9,10-bis(N,N-dialkylamino)anthracene (BDAA) and the corresponding mechanistic analysis by quantum chemical calculations. BDAA comprises an anthracene core and small electron donors, which allows the quantum chemical aspects of AIE to be discussed. The key factor for AIE is the control over the non-radiative decay (deactivation) pathway, which can be visualized by considering the conical intersection (CI) on a potential energy surface. Controlling the conical intersection (CI) on the potential energy surface enables the separate formation of fluorescent (CI:high) and non-fluorescent (CI:low) molecules [control of conical intersection accessibility (CCIA)]. The novelty and originality of AIE in the field of photochemistry lies in the creation of functionality by design and in the active control over deactivation pathways. Moreover, we provide a new design strategy for AIE luminogens (AIEgens) and discuss selected examples.

Design and development of fluorescence-capable novel pyrazine-based polycyclic heteroaromatics for cellular bioimaging

Fluorescence-capable pyrazine-based polycyclic heteroaromatics for application in bioimaging were synthesized via a simple and concise methodology, and investigation of their fluorescence properties, including the effect of pH on the fluorescence behaviour, and MTT assays were carried out.