Molecular functions depend on conformations and motions of the corresponding molecular species. An airwater interfacei sasuitablea symmetricf ield for the control of molecular conformationsa nd motions under as mall applied force. In this work, double-paddled binuclear Pt II complexes containing pyrazole rings linked by alkyl spacers were synthesized and their orientations and emission properties dynamically manipulateda tt he air-water interface. The complexese merge from water with concurrent variation of interfaceo rientation of the planes of the Pt II complexes from perpendicular to parallel during mechanical compression suggesting au nique 'submarine emission'. Phosphorescence of the complexes is quenched at the air-water interface prior to monolayer formation with intensities subsequently rapidly increasing during monolayer compression. These results indicate that asymmetricr eactions andm otionsm ight be controlled by applying mechanical force at the air-water interface.

We aim to establish the importance of molecular design for the formation of monolayers at an air-water interface within the concept “coordination amphiphile”, which is based on ligand characteristics and molecular topology. For this purpose, five types of platinum complexes containing a coordination plane, including salicylaldiminato (SA) and β-(iminomethyl)azolato (IA) complexes, were prepared where the ligand characteristics were controlled. Polymethylene-vaulted and non-vaulted complexes were then examined to assess the effects of molecular topology on interfacial activity. SA complexes tend to undergo random aggregation at an air-water interface, while the weak hydrophilicity of SA can assist in the formation of a stable monolayer if hydrophobic and hydrophilic chains are introduced to the structure. In contrast, IA complexes exhibit topological specificity; imidazolato and pyrazolato complexes form monolayers only for non-vaulted and vaulted complex, respectively. Molecular modelling and association constants of the compounds suggest that an appropriate hydrophilicity of the coordination plane and intermolecular interactions involving hydrogen bonding are important factors for monolayer formation.

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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 AnP 2 -H and AnP 2 -OEG, both of which contain 9,10-di(piperazinyl)anthracene, based on 9,10-bis(N,Ndialkylamino)anthracene that adopts a nonflat geometry at minimum energy conical intersection. AnP 2 -H and AnP 2 -OEG exhibited enhanced fluorescence as the viscosity increased, with sensitivities comparable to those of conventional molecular rotors. In living cell systems, AnP 2 -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.

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 is an aggregation-induced emission luminogen (AIEgen). 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.