Electrochemically induced hyperfluorescence based on the formation of charge-transfer excimers

Used extensively in sensing applications, the application of solution-state electrochemiluminescent devices (ECLDs) in lighting and displays has been constrained by their low luminance and short operational lifetime. Here, we introduce ECLDs based on electrochemically induced hyperfluorescence (ECiHF), and demonstrate their use in a calligraphic display. We use the double-decker arrangement assumed by the electron donor and acceptor segments of the molecule TpAT-tFFO to realize thermally activated delayed fluorescence from an electrogenerated charge-transfer excimer state. ECLDs based on this strategy achieve improved efficiency, a luminance of >6200 cd m^-2 and their operational lifetime is more than 10-fold longer than all previous ECLDs with meaningful efficiency or brightness. Using spectroelectrochemical analysis, we identify energy level alignment between excimer and emitter as a crucial factor for efficient ECiHF. Our findings highlight the potential of ECiHF for improving ECLDs and pave the way to commercial applications of this form of fluid light.