Fluorescence

[piraterach]

Why is fluorescence seen more in fused aromatic rings??

[theprof]

Hmm. Fairly advanced stuff this. This is one of those questions where it's desirable to know the level of your knowledge before answering.

What course are you following?

[piraterach]

Hi I'm doing forensic sciences at university. Need to understand this question so I can write a report. Thanks

[theprof]

I see.

Well, most fluorescent organic molecules possess conjugated double bonds and conjugated aromatic molecules are almost always reactive. This is because the pi-electrons are readily polarizable due to their relative distance from the carbon nuclei, and are hence capable of easily forming new chemical bonds. In addition, by their very nature, they are less strongly bound within the molecule than the sigma electrons.

It should also be noted that during excitation of aromatic molecules, the electron cloud is provided with extra energy which will allow to do such things as change of isomerism of double bonds, charge transfers, proton transfer as well as the initiation of photochemistry and fluorescence.