text: A molecular logic gate can processes modulators much like the setup seen in de Silva’s proof-of-principle, but incorporating different logic gates on the same molecule is challenging. Such a function is called integrated logic and is exemplified by the BODIPY-based, half-subtractor logic gate illustrated by Coskun, Akkaya, and their colleagues. When monitored at two different wavelengths, 565 and 660 nm, XOR and INHIBIT logic gates operations are realized at the respective wavelengths. Optical studies of this compound in THF reveal an absorbance peak at 565 nm and an emission peak at 660 nm. Addition of an acid results in a hypsochromic shift of both peaks as protonation of the tertiary amine results in an internal charge transfer. The colour of the emission observed is yellow. Upon the addition of a strong base, the phenolic hydroxyl group is rendered deprotonated, resulting in a photoinduced electron transfer, which in turn renders the molecule non-emissive. Upon addition of both an acid and a base, the emission of the molecule is observed as red, as the tertiary amine would not be protonated while the hydroxyl group would remain protonated, resulting in the absence of both PET and intramolecular charge transfer (ICT). Due to the great difference in emission intensity, this single molecule is capable of carrying out an arithmetic operation - subtraction - at a nanoscale level.
  A full adder system based on fluorescein has also been constructed by Shanzer et al. The system is able to compute 1+1+1=3.