Fluorescence Turn-On Response Amplified by Space Confinement in Metal–Organic Frameworks Xue-Mei Yin Lu-Lu Gao Peng Li Ran Bu Weng-Jie Sun En-Qing Gao 10.1021/acsami.9b18307.s001 https://acs.figshare.com/articles/journal_contribution/Fluorescence_Turn-On_Response_Amplified_by_Space_Confinement_in_Metal_Organic_Frameworks/11310497 Sensitive fluorescence turn-on response to specific substances is highly desired for development of chemical sensors and switches. Here we utilized a “two-in-one” strategy to prepare ionic metal–organic frameworks (MOFs) functionalized with the cationic bipyridinium receptors at the frameworks and anionic fluorescent indicators in the pores. The MOFs are rendered a fluorescence-resting state because the indicator’s fluorescence is efficiently quenched by the ground-state charge-transfer (CT) complexation between the indicator and receptor. Addition of an alkylamine efficiently turns on the fluorescence because the indicator is displaced by the CT complexation between alkylamine with receptor. The turn-on response is highly specific to alkylamines. The MOFs can be used as recyclable sensors for selective and sensitive detection of alkylamines, with ultralow detection limits (0.5 nM). The fluorescence in solid state can be reversibly switched on and off with high contrast. The sensitive and high-contrast response can be attributed to the space confinement effects of the porous frameworks. The confined space can significantly enhance indicator–receptor and analyte–receptor interactions, and thereby both the quenching efficiency in the off state and the displacement efficiency in the on state are amplified. 2019-12-03 15:24:06 detection Fluorescence Turn-On Response Amplified indicator CT complexation space confinement effects fluorescence turn-on response chemical sensors quenching efficiency high-contrast response displacement efficiency framework turn-on response Space Confinement alkylamine cationic bipyridinium receptors fluorescence-resting state ground-state charge-transfer MOF