Conjugated pi-bond system chromophores Chromophore

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conjugated chromophore straightens in response photon γ (light), of correct wavelength: 11-cis-retinal becomes all-trans-retinal


in conjugated chromophores, electrons jump between energy levels extended pi orbitals, created series of alternating single , double bonds, in aromatic systems. common examples include retinal (used in eye detect light), various food colorings, fabric dyes (azo compounds), ph indicators, lycopene, β-carotene, , anthocyanins. various factors in chromophore s structure go determining @ wavelength region in spectrum chromophore absorb. lengthening or extending conjugated system more unsaturated (multiple) bonds in molecule tend shift absorption longer wavelengths. woodward-fieser rules can used approximate ultraviolet-visible maximum absorption wavelength in organic compounds conjugated pi-bond systems.


some of these metal complex chromophores, contain metal in coordination complex ligands. examples chlorophyll, used plants photosynthesis , hemoglobin, oxygen transporter in blood of vertebrate animals. in these 2 examples, metal complexed @ center of tetrapyrrole macrocycle ring: metal being iron in heme group (iron in porphyrin ring) of hemoglobin, or magnesium complexed in chlorin-type ring in case of chlorophyll. highly conjugated pi-bonding system of macrocycle ring absorbs visible light. nature of central metal can influence absorption spectrum of metal-macrocycle complex or properties such excited state lifetime. tetrapyrrole moiety in organic compounds not macrocyclic still has conjugated pi-bond system still acts chromophore. examples of such compounds include bilirubin , urobilin, exhibit yellow color.








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