Chapters 14 & 15

1. Chapters 14 & 15

2. UV-Vis

3. Nature of Absorption • Absorbs EM radiation from a source, like a D2 and Tungsten lamp • Electrons relax back to ground state

4. Solvent Effects • Choose solvent based on transparency and effects on the system • Polar solvents tend to mask fine structure • Non-Polar solvents tend to keep the general peak arrangements, and skew the spectra • Analyzing without solvent (Neat) is always the best

5. Organic Absorption • All organics can absorb EM radiation • Chromophores – molecules that contain such functional groups and are capable of absorbing at UV radiation • Functional groups have pi orbitals that help it absorb

6. Inorganic Absorption • Absorbing results in exciting non-bonding orbitals into the pi* orbitals

7. Charge-Transfer Absorption • Leads to a large molar absorptivity • Electron donor bonds to electron acceptor • Donor loses electron when excited, and acceptor takes it

8. Luminescence

9. Block Diagram

10. Fluorescence • Excited to singlet state • Stabilizes to singlet ground state, then relaxes down to ground state • Relaxation causes emission of radiation • Lasts a short time

11. Phosphorescence • Electrons cross into a triplet state from singlet state • In triplet state electron spins are unpaired, spinning in the same direction • Once stabilized to the triplet ground state, electrons relax back to ground state • This releases radiation, and lasts longer then fluorescence

12. Chemiluminescence • Luminescence cause by chemical reaction • Not a lot of analytes that do this • Emits light when relaxing • More common in a biological setting, ex. fireflies

13. Selectivity • Rigidity effects how well it absorbs, more rigidity means more fluorescence • Compounds with aromatic functional groups that have low pi to pi* provide intense fluorescence

14. Components • Sources • Lamps • Laser • Monochromators • Transducers • Photomultiplier tubes • Cells • Quartz is best • Silica • Plastic