CHAPTERS 14 & 15

UV-Vis

Nature of Absorption

Absorbs EM radiation from a source, like a D2 and Tungsten lamp

Electrons relax back to ground state

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

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

Inorganic Absorption

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

Charge-Transfer Absorption

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

acceptor takes it

Luminescence

Block Diagram

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

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

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

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

Components

Sources Lamps Laser

Monochromators Transducers

Photomultiplier tubes Cells

Quartz is best Silica Plastic