Molecular logic devices (half-subtractor, comparator, complementary output circuit) by controlling photoinduced charge transfer processes

The fluorescence properties of a naphthalene derivative with a methoxy and a pyridyl substituent were investigated, including the influence of protons, electron-donating amines, and dihydrogenphosphate anions. The naphthalene derivative shows strong fluorescence with a maximum at 353 nm, which can be quenched by amines through a diffusion-controlled photoinduced electron transfer. Protonation of the pyridyl residue leads to the observation of a red-shifted broad emission at 470 nm, which has been assigned to an internal charge transfer state. The interpretation of the fluorescence behaviour in the presence or absence of the chemical inputs leads to the realisation of unimolecular logic circuits, which are able to perform advanced arithmetic operations such as subtraction (XOR/INH combination) and comparison (XNOR/INH combination). Furthermore, a complementary output circuit (INH/IMP combination) was implemented. The implicated logic gates can be reconfigured, either by application of different input sets or by varying the fluorescence output observation wavelength. The system works in an all-fluorescence output mode, which leads to a superposition of the gates. This is of particular advantage as it allows reading out without any time lag, which is a commonly encountered problem in silicon circuitry based on electrical signals.