A New Biphotochromic Fluorescent Switch Based on Dithienylethene and Triphenylethylene: Synthesis, Crystal Structure, and Optical Waveguide

Abstract A novel biphotochromic fluorescent switch molecule N‐2F derived from dithienylethene (DTE) and triphenylethylene (TPE) is reported. Interestingly, different photochromic and fluorescence phenomena of N‐2F are observed in tetrahydrofuran/water mixtures. When f w ≤ 50%, N‐2F shows effective photochromic and fluorescent switch under alternating with 254 and 500 nm light irradiation due to the DTE unit undergoing reversible cyclization and cycloreversion reactions between its open and closed forms. However, when f w ≥ 60%, the strong blue‐green fluorescence of the original solution is almost quenched under 254 nm light irradiation, but becomes red fluorescent emission under 500 nm light irradiation. When further irradiated with 254 nm, the red fluorescent emission disappears, but it reappears upon 500 nm light illumination. The results reveal that DTE and TPE take cyclization and cycloreversion reactions upon alternating with 254 and 500 nm light irradiations, and TPE will take dehydrogenation reaction with further 254 nm irradiation. Moreover, N‐2F can easily obtain long length (about 2 cm) rod single crystal with high fluorescence quantum yield of 68.97%. Impressively, N‐2F shows excellent optical waveguide with very low loss coefficient of 0.171 dB mm −1 . Therefore, N‐2F exhibits potential applications in anti‐counterfeiting, multi‐color display, and functional photonic devices.