XPost: sci.chem   
   From: a202010@lycos.com-   
      
   Salmon Egg wrote:   
      
   >  Timothy Sutter  wrote:   
      
   > > but, if you broke off the chromophore or the auxochrome   
   > > from the dye molecule, and looked at it in isolation,   
   > > you would probably find that these functional groups   
   > > had no 'color' of their own.   
      
   > > there's a lot of similarities,   
      
   > > why don't you make up an analogy?   
      
      
   > Sorry. I responded to this poster before reading it entirely. I   
   > apologize.   
      
   > The activator can undergo considerable absorption line shifts. Cr+++ can   
   > emit red in ruby and green in alexandrite.   
      
   right, but chromophores like nitro, carbonyl, halide,   
   and ethylene groups don't have much color in 'isolation'   
   nor do auxochromes like carboxyl, hydroxyl, sulfonic acid   
    and amine groups.   
      
      
      
   > I think of the chromophore as being an antenna corresponding to   
   > conductivity along chains or other paths because of electrons or holes   
   > induced by auxochromes donating or receiving an electron. The resonant   
   > frequency, if it were classical, will be decreased as the conducting   
   > chain gets longer. Quantum mechanically, this corresponds to finding the   
   > eigenvalues of an electron in a box potential.   
      
      
   i have no real problem with the antenna idea.   
   it all has something to do with the energy differences   
   between occupied and unoccupied molecular orbitals.   
      
   the so-called HOMO/LUMO gap   
      
   highest occupied molecular orbital/   
     /lowest unoccupied molecular orbital   
      
   if you could use functional group attachment   
   to dial that gap to precise energies, then   
   you could dial up any color you want.   
      
   i would think that the auxochrome sort of   
   tunes the 'homo/lumo' gap in the chromophore   
      
      
   i'd think that the auxochromes are donating   
   or withdrawing electrons in pairs into conjugated   
   pi systems and extending the conjugation and that   
   the individual electrons that are jumping the gap   
   come from the chromophore, because you can see color   
   in the absence of an auxochrome, but the auxochrome   
   tends to intensify the color by tuning the gap.   
      
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