Physical 7

Physical 7

1. absorption of energy

   • how matter takes up a photons energy
     • absorb it and change their electronic state
       • light is absorbed and electric field of light induces change
       • charge separation- transition dipole moment
         • electronic orbital
           • move quicker than nuclei
         • spin components
         • nuclear
         • movement of electrons
         • any integral is 0= spin forbidden
   • frequency is near the energy levels of the electrons
     • UV or visible
     • infrared
       • vibrational
   • measuring absorption
     • beer lambert law

2. chromophore

   • measure oscillator strength
     • express strength of electric dipole transition
       • 3D
     • 0-spin forbidden
     • fnm
   • molecules that interact with light to give colour
     • large
     • highly conjugated
   • rigidity of chromophore
     • vibrational structure
       • decrease in temp
       • immobilization on solid support
     • increase in viscosity of sol
   • excitation of chromophore leads to redistribution of electron density
     • so solvent relaxation occurs
       • reorientation of solvent
         • establish favourable electronic interaction

3. rotational energy

   • E=BJ(J+1)
   • microwave
   • far-infrared

4. vibrational energy

   • e=ωe(v+1/2)
   • infrared
   • nuclear

5. Electronic

   • visible
   • UV
   • energies are high enough
     • bond dissociation and ionisation occurs
   • photochemistryin this region

6. selection rules

   • spin
     • magnetic spin +orbital angular momentum
       • spin-orbit coupling
         • strength proprtional to atomic mass
       • magnetic causes1->3 to occur
   • symmetry
     • electronic and vibrational couple
       • distort molecular symmetry
         • forbidden transitions are weakly allowed

7. transition probabilities

   • dependent on Frank-Condon principle
   • intensity of transitions is proportional to square of overlalp of GS and ES
   • absorption is wavelength dependent
   • transitions are vertical
   • occur with varying probabilities
   • transitions between electronic states of different spin multiplicities are weakly allowed
     • require inversion of spin quantum number

8. rate of transitions

   • radiation absorbed by matter during a transition
     • stimulated absorption
     • stimulated emission
     • spontaneous emmision

9. polar solvents

   • stabilise GS but detabilise ES
     • Hypochromic shift- large energy gap
     • align dipoles
   • Apolar solvent
     • destabilise ES but stabilise GS
       • bathochromic shift-small energy gap
       • unbalance dipoles
   • chromophore2

10. fluorophores

    • detected at single molecule level