Figure shows UV excitation writable paper coated with a TPA-CO2H/PVA film, suitable for optical information communication at night, Video S3. Photo-printing can be realized when a mask is placed on the prepared TPA-CO2H/PVA board (Figure , Videos S4 and S5). As shown in Figure , the panda pattern and the logo "University of St Andrews" show a bright blue afterglow after switching off the UV lamp. Information encryption is also possible based on the afterglow ink made from a TPA-CO2H/PVA water solution. For example, the number "1413", the year of the founding of the University of St Andrews, cannot be identified by the naked eye either under ambient lighting conditions or under 365 nm UV excitation; however, the information becomes visible only once photoexcitation ceases.