A photochemical logic gate is based on the photochemical intersystem crossing

Intersystem crossing

Intersystem crossing is a radiationless process involving a transition between two electronic states with different spin multiplicity.-Singlet and triplet states:...

 and molecular electronic transition

Molecular electronic transition

Molecular electronic transitions take place when electrons in a molecule are excited from one energy level to a higher energy level. The energy change associated with this transition provides information on the structure of a molecule and determines many molecular properties such as color...

 between photochemically active molecules, leading to logic gates that can be produced.
_A*                    A* = excited state of molecule A

       _B*

            _C*

_A  _B  _C

The OR

Logical conjunction

In logic and mathematics, a two-place logical operator and, also known as logical conjunction, results in true if both of its operands are true, otherwise the value of false....

 gate is based on the activation of molecule A, and thus pass electron

Electron

The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

 / photon

Photon

In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

 to molecule C’s excited state orbitals ( C*).