Microcavity-Enhanced Directional Electrochemiluminescence Output from Single Molecular Crystals

Molecular crystal-based electrochemiluminescence (ECL) waveguides can output directional optical signal. However, an optical loss still exists, suppressing the output strength. Herein, we report an approach of achieving enhanced ECL output by ingeniously designing microrod-shaped molecular crystals with microcavities at both terminals, termed as mMCs. A combined use of band electrode array and ECL microscopy allows both the spatially selective electrochemical excitation of single mMCs to generate ECL and the imaging study of light propagation along the crystals. When triggering ECL reactions at one terminal of mMCs, the light can be transmitted to the other. Compared with solid molecular crystals with an ECL loss of up to 93%, the optical loss in mMCs can be reduced to 15% (left to right) and 81% (right to left). Furthermore, when ECL is triggered at the middle of mMCs, the ECL propagation is lossless and even remarkably improved by 1.7-6.8 times, thus realizing the enhanced directional optical output, thanks to the open microcavities that favor the out-coupling of light from the molecular crystal. This finding demonstrates a controllable approach for the microcavity-enhanced directional ECL output and holds great promise in remote and intercellular imaging through ECL waveguiding.