Ferrocene–Dithienylethene–Naphthalenediimide-Based Multifunctional Molecular Switch: Applications in Anticounterfeiting and Controlled Singlet Oxygen Generation

Reversible switching of fluorescence using a multiresponsive channel has received significant attention for its wide range of applicability in optoelectronics, molecular memory devices, sensing, logic operation etc. Here, a ferrocene-dithienylethene-core-substituted naphthalene diimide (Fc-DTE-cNDI) triad has been fabricated to obtain a dual mode (photochromic and redox) of reversible fluorescence switching. The photochromic fluorescence switching was achieved via modulation of the FRET mechanism between the open and closed isomeric forms of the dithienylethene unit. The photocyclization and cycloreversion processes displayed a good photoisomerization quantum yield (ΦO→C = 0.32 and ΦC→O = 0.089) in solution as well as in the solid state. Another switching channel was achieved by reversible modulation of the photoinduced electron-transfer (PET) process between ferrocene and cNDI units using Fe(ClO4)3 and NH2OH·HCl as chemical stimuli. The modulation of PET process by switching the oxidation state of iron in ferrocene and the photochromic isomerization via FRET, established a dual mode of the fluorescence switching phenomenon. The developed molecule was capable to withstand minimum 45 cycles of consecutive UV and visible light irradiation in solution and solid states, demonstrating its excellent fatigue resistance property. Thus, anticipating the efficient dual switching capability, Fc-DTE-cNDI was successfully applied in a secret code encryption–decryption technique and in the controlled singlet oxygen generation process.