 Absorbs EM radiation from a source, like a D 2 and Tungsten lamp  Electrons relax back to ground state

 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

 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

 Absorbing results in exciting non-bonding orbitals into the pi* orbitals

 Leads to a large molar absorptivity  Electron donor bonds to electron acceptor  Donor loses electron when excited, and acceptor takes it

 Excited to singlet state  Stabilizes to singlet ground state, then relaxes down to ground state  Relaxation causes emission of radiation  Lasts a short time

 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

 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

 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

 Sources  Lamps  Laser  Monochromators  Transducers  Photomultiplier tubes  Cells  Quartz is best  Silica  Plastic