Fast and Reversible Red Emission Modulation in Photoswitchable Molecules Toward Optical Data Storage

Abstract Photoswitchable dithienylperfluorocyclopentene (DCP) and dibenzothienylperfluorocyclo‐pentene dioxide (BTCPO4) have potential applications in optical data storage. They exhibit high fatigue resistance and reverse ON‐OFF photoswitching of emission due to ring opening and closing reactions, feasible at two different wavelengths. DCPs are non‐emissive in both the open and closed states, whereas BTCPO4s are emissive upon ring closure. There is a scarcity of fast, reversible, and bistable photoswitchable red emitters. Therefore, a series of red‐emitting BTCPO4s is synthesized, and their detailed photophysical characterization is reported here. This study shows that the red emitters are highly stable in the cyclized form, requiring high laser power and long irradiation times for reverse cyclization to the non‐emissive state. Also, the ON‐OFF contrast ratio is very low. To enable red emission modulation and to increase the contrast ratio, energy transfer from the red‐emitting BTCPO4 isomer to a fast photoswitchable non‐emitting DCP molecule is exploited. This novel approach enables 60 times faster, reversible modulation of the red emission with a four times higher contrast ratio (≈90%) and at 150 times lower visible laser irradiation intensity than can be achieved for the pure red emitter alone. Finally, the potential for optical data storage is demonstrated for 100 write‐read‐erase cycles.