Why do aromatics exhibit fluorescence & scintillation?

I'm currently trying to figure out exactly why aromatics (e.g. polyvinyl toluene [PVT], polystyrene [PS], anthracene) fluoresce and scintillate...

I know that its got something to do with the pi system causing dense clouds of electrons to form in the ring(s), and that the addition of a methyl group to PS [i.e. PVT] increases the density of electrons in the ring which is why PVT is generally more widely used than PS in plastic scintillators (albeit with them both doped slightly with anthracene)........

Also, why are PS / PVT scintillators usually doped with anthracene?  I'm thinking something along the lines of resonance energy transfer to improve quantum efficiency.

Beyond that, I can't quite fathom why this allows it to scintillate.....

My understanding of fluorescence is that excited electrons/atoms/molecules relax thermally to S1, then a proportion of those relax with emission from S1 -> S0 - so why would several scintillation photons be produced by a single X-ray photoelectric interation?
Does the photoelectron then excite many more electrons, or does it just emit several photons as it relaxes (e.g. S3->S2 then S2->S1, S1->S0)?


Thanks in advance, and if you could advise me on any relevant books / papers, that would be great!

-Mark