Optoelectronic behavior of bischromophoric dyads exhibiting Zn2+/F− ions induced “turn-On/Off” fluorescence

Some bischromophoric dyads containing anthracene and naphthalic anhydride moieties have been designed and synthesized. The optical behavior of dyads and their interaction with ions (cation/anion) have been investigated through absorption, fluorescence, NMR, and ESI-MS spectral analysis. Dyads 8 and 9 have shown weak emission at ∼525-530 nm in MeCN-H2O medium. Depending upon the length of spacer arm dyads 8 and 9 upon interaction with various metal ions exhibited affinity for Zn2+ ions in which the relative fluorescence intensity of 8 enhanced ∼5 times (switched-On) with the increase in the quantum yield (∼4 times) and a naked-eye sensitive blue color appeared in the solution. Further, 8 upon interaction with anions in acetonitrile illustrated fluorescence quenching (71%) with F− ion only. The observed enhanced and quenched emissions in the presence of Zn2+ and F− ions may be attributed to restricted and enhanced PET reactions probably, due to the complexation and deprotonation of NH fragment present at the aminoalkyl linker arm, respectively. Job's plot analysis revealed a 1:1 stoichiometry between dyad 8 and Zn2+/F− ions and association constants estimated by Benesi-Hildebrand method were found to be Kassoc = 1.23 × 104 M−1 and 2.2 × 104 M−1 respectively.