Installing hydrogen bonds as a general strategy to control viscosity sensitivity of molecular rotor fluorophores Special Collection:Aggregation-Induced Processes and Functions

Molecular rotor-based fluorophores(RBFs)activate fluorescence upon increase of micro-viscosity,thus bearing a broad application promise in many fields.However,it remains a challenge to control how fluorescence of RBFs responds to viscosity changes.Herein,we demonstrate that the formation and regulation of intramolecular hydrogen bonds in the excited state of RBFs could modulate their rotational barrier,leading to a rational control of how their fluorescence can be activated by micro-viscosity.Based on this strategy,a series of RBFs were developed based on 4-hydroxybenzylidene-imidazolinone(HBI)that span a wide range of viscosity sensitivity.Combined with the AggTag method that we previously reported,the varying viscosity sensitivity and emission spectra of these probes enabled a dualcolor imaging strategy that detects both protein oligomers and aggregates during the multistep aggregation process of proteins in live cells.In summary,our work indicates that installing intracellular excited state hydrogen bonds to RBFs allows for a rational control of rotational barrier,thus allow for a fine tune of their viscosity sensitivity.Beyond RBFs,we envision similar strategies can be applied to control the fluorogenic behavior of a large group of fluorophores whose emission is dependent on excited state rotational motion,including aggregation-induced emission fluorophores.

Synergistic effects of multiple rotors and hydrogen-bond interactions lead to sensitive near-infrared viscosity probes for live-cell microscopy

Changes in cellular viscosity are associated with various physiological processes and pathological conditions.To study these cellular processes and functions,highly sensitive fluorescent probes that detect subtle changes in viscosity are urgently needed but remain lacking.In this study,we present a series of viscosity-responsive near-infrared(NIR)fluorescent probes based on styrene-coated boron dipyrromethene(BODIPY).The probe modified with dimethylaminostyrene and piperazine at the two terminals of the BODIPY scaffold showed extremely high viscosity sensitivity values(x,around 1.54),with excellent performance for detecting viscosity below 20 c P.This outstanding property is attributed to the synergistic effects of multiple rotatable bonds and hydrogen-bond interactions.Additionally,this probe has been successfully deployed to monitor viscosity changes in various cellular compartments(i.e.,cytoplasm)and processes(such as during autophagy).This work provides a rational molecular design strategy to construct fluorescent probes with high viscosity sensitivity for exploring cell functions.