Fluorescent molecular rotors (FMRs) can act as viscosity sensors in various media including subcellular organelles and microfluidic channels. In FMRs, the rotation of rotators connected to a fluorescent π-conjugated bridge is suppressed by increasing environmental viscosity, resulting in increasing fluorescence (FL) intensity. In this minireview, we describe recently developed FMRs including push–pull type π-conjugated chromophores, meso-phenyl (borondipyrromethene) (BODIPY) derivatives, dioxaborine derivatives, cyanine derivatives, and porphyrin derivatives whose FL mechanism is viscosity-responsive. In addition, FMR design strategies for addressing various issues (e.g., obtaining high FL contrast, internal FL references, and FL intensity-contrast trade-off) and their biological and microfluidic applications are also discussed.
O.-P. K. thanks the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning and Ministry of Education, Korea (No. 2014R1A5A1009799 and 2009-0093826). C.-L. L. thanks the National Research Foundation of Korea (NRF) for financial support through a grant funded by the Korean government (MSIP; NRF2016R1A2B4013003) and a grant funded by GIST 2018 (Research on Advanced Optical Science and Technology). S. K. thanks the Korea Health Industry Development Institute (HI15C1540), and Korea Research Institute of Standards and Science (Development of Platform Technology for Innovative Medical Measurements Program, KRISS-2017-GP2017-0020) for financial supports.
