Dual-Mode Photochromic Luminescence of Carbon Dots Induced by Photoinduced Electron Transfer
The integration of photochromism and photoluminescence in a single material platform remains constrained by insufficient photostability, slow response kinetics, and limited reversibility. This work reports sodium-doped and sodium/boron co-doped carbon dots (CDs) that exhibit dual-mode photochromic luminescence via a radical-mediated photoinduced electron transfer (PET) mechanism. Na-CDs display a 180 nm red-shift in emission from 450 to 630 nm under 365 nm excitation. Na,B-CDs achieve blue-shifted multicolor emission progressing from orange to yellow and green within 30 s of UV irradiation. The photochromic states spontaneously revert to their initial configurations without external stimuli, and the process remains reversible over multiple cycles. The phenomenon originates from PET between pristine CDs and light-generated anionic radicals. Exploiting these properties, the authors demonstrate reversible anti-counterfeiting systems, information encryption platforms, daylight-responsive UV detection, and plant cell imaging. Na-CDs-PVA films exhibit rapid darkening under sunlight (UV index = 6) and recover after sunset. Na,B-CDs serve as cryptographic security inks for monochrome printing, enabling message decryption through photochromic color changes. Fluorescence imaging of mung bean sprout cells shows blue-to-orange transitions under 365 nm irradiation. These results establish CDs as viable candidates for optoelectronic devices, security labeling, and bioimaging, though long-term photostability and scalable manufacturing remain to be validated.