All-photonic inputs

2-ns delay would matter in devices running near GHertz rates. Nevertheless 37 is a rather fast gate since it resets in 25 ns. 

Wasielewski s previous publication on 38 [93, 94] was the forerunner of the discussion concerning 37 [90]. The donor-acceptor molecule 38 was capable of a fast switch with potential logic capabilities. The two terminal porphyrin donor moieties could independently reduce the central perylene tetracarboxydiimide acceptor moiety via PET. When only one porphyrin was excited by a femtosecond laser pulse, the absorption due to the perylene tetracarboxydiimide radical anion was seen. If both porphyrins were excited simultaneously by a higher intensity laser pulse, two PET processes to the central acceptor could occur, giving a dianion with a different absorption band. 

The gate 39 [95] mentioned above gave almost equal fluorescence enhancements when sufficient quantities of K or Rb were added, probably for a similar reason as for 40. The relative rigidity of the cryptand moiety exacted a price. Only when 

Gate 42 [97] is interesting because various transition metal ions serve to switch on fluorescence by more-or-less same amounts. The surprise in this system [97, 98] is that transition metal ions were acting contrary to their normal behaviour. Transition metal ions have a history of quenching fluorescence very efficiently by several mechanisms heavy atom effects, PET, electronic energy transfers and 

The pyrene-based fluorescence of Pages 45 [104] was switched off by Zn . H should give a similar result, thereby recognizing 45 as a NOR logic gate. 

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