“…11–35 Fluorescence-based optodes are typically more sensitive than colourimetry-based optodes. The response mechanism of fluorescence-based optodes containing organic fluorophores can be classified based on the fluorescence mechanism 18,19 into photo-induced electron transfer (PET), 20–24 intramolecular charge transfer (ICT), 21,25–28 twisted ICT (TICT), 26,29,30 aggregation-induced emission (AIE), 24,29,30,32,33 and excited-state intramolecular proton transfer (ESIPT), 31,34,35 and so on. In addition to the organic-fluorophore-based water detectors, other luminescent inorganic and/or organic water detectors – such as graphene quantum dots, 36 carbon dots (CDs), 37–40 covalent organic frameworks (COFs), 41–44 and metal–organic frameworks (MOFs) 39,45–47 – have been developed over the past decade.…”