Molecular engineering of logic gate types by module rearrangement in 'Pourbaix Sensors': the effect of excited-state electric fields

• Published in: Organic & biomolecular chemistry 2018, Vol.16 (34), p.6195-6201
• Main Authors: Spiteri, Jake C, Denisov, Sergey A, Jonusauskas, Gediminas, Klejna, Sylwia, Szaciłowski, Konrad, McClenaghan, Nathan D, Magri, David C
• Format: Article
• Language: English
• Subjects: Chemical Physics; Electrons; Field programmable gate arrays; Fluorescence; Fluorescence spectroscopy; Gates; Iron; Logic circuits; Physics; Signal reconstruction
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/c8ob00485d

Two types of fluorescent logic gates are accessed from two different arrangements of the same modular components, one as an AND logic gate (1) and the other as a PASS 0 logic gate (2). The logic gates were designed with an 'electron-donor-spacer1-fluorophore-spacer2-receptor' format and demonstrated in 1 : 1 (v/v) methanol/water. The molecules consist of ferrocene as the electron donor, 4-aminonaphthalimide as the fluorophore and a tertiary alkylamine as the receptor. In the presence of high H+ and Fe3+ levels, regioisomers 1a and 1b switch 'on' as AND logic gates with fluorescence enhancement ratios of 16-fold and 10-fold, respectively, while regioisomers 2a and 2b are functionally dormant, exhibiting no fluorescence switching. The PASS 0 logic of 2a and 2b results from the transfer of an electron from the excited state fluorophore to the ferrocenium unit under oxidising conditions as predicted by DFT calculations. Time-resolved fluorescence spectroscopy provided lifetimes of 8.3 ns and 8.1 ns for 1a and 1b, respectively. The transient signal recovery rate of 1b is ∼10 ps while that of 2b is considerably longer on the nanosecond timescale. The divergent logic attributes of 1 and 2 highlight the importance of field effects and opens up a new approach for regulating logic-based molecules.