Would someone be able to explain how the light-sensitive organic molecule methylene blue breaks down under photonic illumination? I often see reports of oxidisation, but this is a reversible process and not an outright breaking of the methylene blue molecule. 

I know that the 664nm absorption resonance is due to a transition from the nonbonding state to the antibonding state. Does the antibonding state weaken the bond so much so that the molecule is broken more easily somehow? 

Many thanks in advance! 

Note, I am looking to see how it goes permanently colourless. Leucomethylene blue (whilst colourless) is not a permanent degradation. In addition, demethylation by hydrogen abstraction - though a common procedure - does not turn the solution colourless. 

Figured it out now, not to worry