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Colours and chromophores - Coggle Diagram

- - - - these colours can be seen when white light passes through a prism
    - - infrared
      - UV light
    - - ~ 350 - 750 nm
        
        colours of the rainbow
        
        subtractive colour model
        
        says that the colour we see is the one that is reflected
        
        the object absorbs the opposite colour on the colourwheel, making it not appear
        
        ex: red and green
        
        if object is white, all colours are reflected back
        
        if object is black, all the colours are absorbed
        
        if 2 complementary(opposite) colours are absorbed, all other colours are reflected back, making the object appear white
  - - - shining light on object with colour that absorbs the the monochromatic light well
        
        ex: complementary colour or black
        
        colour appears faint or is now black (only if fully absorbed)
      - shining light on object with colour that does not absorb the the monochromatic light well
        
        ex: same colour, white or any colour that is not the complementary colour
        
        colour is reflected brightly
- - - - absorption spectrum
        
        shows the amount of light absorbed at a specific wavelength
        
        for a molecule, the highest maxima is the wavelength of max absorption
        
        chromophores
        
        molecules with functional groups/ parts that absorb light
        
        common properties
        
        have extended conjugation
        
        alternating double/single bonds
        
        can also say the p orbitals are in the same phase and can connect
        
        are polar/charge groups
        
        when a molecule absorbs light, an e- is promoted to a higher level (either to LUMO or higher)
        
        S1 state
        
        e- goes to LUMO
        
        S2 state
        
        e- goes to 1 higher
        
        1 more item...
        
        energy states
        
        light absorption is viewed a continuum of wavelengths and not discrete
        
        electronic states have vibrational excitation and rotational excitation states within
        
        narrowing the HOMO LUMO gap
        
        if molecule has more conjugation
        
        the HOMO LUMO gap becomes smaller
        
        If there is a break in the conjugation, the molecule's max wavelength acts the same as the conj. of the same size.
        
        with more conjugation, the molecule can start to absorb visible light
        
        the longer the conjugation, the more likely for the molecule to be coloured
        
        1 more item...
        
        if have more polar groups
        
        the HOMO LUMO gap becomes smaller
        
        More polar groups means less conjugation is needed to for the molecule to have colour
        
        the polar groups have resonance that allows the molecule to have a continuous chain of conj.
        
        if narrower gap, a longer wavelength can be used to excite the molecule (easier to reach LUMO from HOMO, requiring less energy)
    - - white light source
        
        monochromator
        
        splitter splits photons
        
        half go straight for detector
        
        half act as incident beam into the solution
        
        beam that comes out is transmitted beam
        
        transmitted beam hits detector
        
        2 more items...
        
        this device allows light of only certain colour/wavelength through
- - - - Intersystem crossing
        
        flipping of an electron spin, putting it in triplet state(which is slightly lower in energy than singlet state)
        
        the same spin electron can then undergo vibrational cooling to v0
        
        phosphorescence
        
        inverts triplet to singlet state
        
        the e- are different spin like before
        
        e- vibrationally cools to v0
        
        can also occur in internal conversion but excited electron falls to v0 in S0 (losing all energy as heat)
        
        slower than fluorescence
      - Energy transfer
      - Internal conversion(ISC)
        
        system quickly falls from S1, v0 to S0, v0
        
        all energy lost as heat
        
        can be fast or slow
        
        good because causes short excitation state, and preventing further UV damage
        
        different from fluorescence
        
        This process falls from S1 v0 to S0, v0, but fluorescence falls to a vx state before v0
      - Chemical reactions
      - Fluorescence
        
        a radiative process that takes nano to micro seconds corresponding of dropping from S1 to S0
        
        The electron returns to homo but not to v0
        
        it is still vibrationally excited but electronically ground
        
        electron can then undergo vibrationally cooling to fall from vx to v0 in ground state
        
        can be measured by a fluorescence spectrometer
        (fluorimeter)
        
        similar to UV vis but measures the emission light of the sample that is perpendicular to the excitation beam
        
        perpendicular shape prevents unabsorbed light from excitation beam from hitting the detector
        
        usually only uses the wavelength that will result in max absorption
        
        the resulting emission wavelength is longer than the absorption because energy is lost as light and light
- - - - when attached to other molecules with conjugation, it changes its emittance colour
        
        a molecule that changes the light absorption properties of the chromophore when attached to it is called an auxochrome
        
        ex: benzoquinone emits yellow itself, but attached to an auxochrome causes it to become red
  - - - allows the 3 rings to be conjugated together
    - - the pheno groups on the aromatic ring are easy to deprotonate
        
        causes molecule to react intramolecularly and expel the ester as an LG
        
        causes the system to have a sp2 carbon and can now have conjugation
        
        other phenol group can then be more easily deprotonated as the charge can be easily stabilized
  - - - chlorophyll
        
        has Mg2+
        
        depending with methyl or aldehyde (add more conj if aldehyde)group at R, determines if is chlorophyll a or b
        
        molecule at the R group is an auxochrome
        
        appears green
        
        has a hydrophobic tail to help add the chlorophyll to the thylakoid membrane
        
        one more ring than meme
      - heme
        
        has Fe2+
      - this is because the number of orbitals and the length of the HOMO LUMO gap changes