Photonic synapses combine sensing and processing in a single device, so they are promising candidates to emulate visual perception of a biological retina. However, photonic synapses with wavelength selectivity, which is a key property for visual perception, have not been developed so far. Herein, organic photonic synapses that selectively detect UV rays and process various optical stimuli are presented. The photonic synapses use carbon nitride (C3N4) as an UV‐responsive floating‐gate layer in transistor geometry. C3N4 nanodots dominantly absorb UV light; this trait is the basis of UV selectivity in these photonic synapses. The presented devices consume only 18.06 fJ per synaptic event, which is comparable to the energy consumption of biological synapses. Furthermore, in situ modulation of exposure to UV light is demonstrated by integrating the devices with UV transmittance modulators. These smart systems can be further developed to combine detection and dose‐calculation to determine how and when to decrease UV transmittance for preventive health care.

Three-dimensional (3D) carbon nitrides (C3N4) show excellent photocatalytic performance for the hydrogen evolution reaction (HER) under visible light irradiation. 3D C3N4 can be produced by the high-temperature polycondensation of small organic compounds, often generating impurities of carbon-based residues for a variety of experimental reasons. The presence of these impurities has resulted in a misunderstanding of the intrinsic properties of C3N4 materials. Therefore, most studies take this impurity for granted and do not attempt to control it. This paper reports that the HNO3 treatment not only removes the inevitable impurity during carbon nitride synthesis, enabling to analyze the intrinsic properties such as morphological, photophysical, and electrochemical characterizations, but also increases dramatically the photocatalytic activity for the HER under visible light irradiation. As a result, the C3N4 material, which is free from C impurity, has favorable crystallinity, surface areas, porosity, electrochemical resistance, and photoluminescence lifetimes for the photocatalytic HER despite the diminishing ability for absorbing visible light. Furthermore, the HNO3-treated C3N4 material shows excellent thermal stability and stable photocatalytic HER activity.

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In article number 1906899, to selectively detect and process UV‐exposure information, Sungjin Park, Tae‐Woo Lee, and co‐workers, demonstrate artificial photonic synapses that emulate the functions of a retina by using a UV‐responsive 2D carbon nitride layer in a floating‐gate transistor. These photonic synapses could expand the human visual sense beyond visible light and be applicable to healthcare devices.

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