Metal ion-induced coordination and cyclization of crown ether-based bisindolylmaleimides: different fluorescence responses and applications in complex logical operations

Molecular logic operations, as the possible alternatives to traditional silicon-based circuitries, are promising in information processing. However, it is difficult to design advanced logic systems based on a simple organic molecule. Here, two kinds of crown ethers, i.e., aza-crown ether and benzo-crown ether were introduced into bisindolylmaleimide (BIM) to give two BIM derivatives: ACE-BIM and BCE-BIM. Both showed weak fluorescence due to the photoinduced electron transfer (PET) effect resulting from crown ethers. The metal ions coordinated with ACE-BIM (such as Hg2+) and BCE-BIM (such as Ca2+) could turn on red luminescence for inhibiting the PET process. Interestingly, the Cu2+ and Fe3+ ions could oxidize the indole rings of ACE-BIM and BCE-BIM to yield cyclization products with green emission. As a result, different loading amounts and sequences of ions severely affected the interactions of coordination and cyclization and eventually the intensities of red and green emissions, which are used to construct various complex logic systems: transfer gates, encoders/decoders, demultiplexers, key lock and combinatorial logic gates with four-input and four-output.