Upload
binh-to
View
217
Download
0
Embed Size (px)
Citation preview
8/8/2019 Optical Properties Test-sua Lai
1/25
Optical properties test
IR and Raman spectroscopy
Ultraviolet spectroscopy NMR spectroscopy
X-ray spectroscopy
8/8/2019 Optical Properties Test-sua Lai
2/25
Symmetric Stretch Antisymmetric Stretch Bend
Infrared spectroscopy
Infrared (IR) spectroscopy measures the bond vibrationfrequencies in a molecule and is used to determine thefunctional group
The bonds between atoms in the molecule stretch and
bend, absorbing infrared energy and creating the infraredspectrum.
8/8/2019 Optical Properties Test-sua Lai
3/25
selection rules
Covalent bonds vibrate at only certain allowablefrequencies.
8/8/2019 Optical Properties Test-sua Lai
4/25
8/8/2019 Optical Properties Test-sua Lai
5/25
An electric dipole moment of the moleculemust change during the vibration
8/8/2019 Optical Properties Test-sua Lai
6/25
Fig 3. spectrum of novolak resin
8/8/2019 Optical Properties Test-sua Lai
7/25
Raman spectroscopy
Is a light scattering technique, and can bethought of in its simplest form as a processwhere a photon of light interacts with a sampleto produce scattered radiation of differentwavelengths
Raman spectroscopy is SCATTERINGspectroscopy Scattering involves amomentary distortion of the electrons distributedaround a molecular bond. Thus, the molecule is
temporarilyPolarized that disappears upon relaxation andreemission. For example, H2 and N2 can be detected
8/8/2019 Optical Properties Test-sua Lai
8/25
8/8/2019 Optical Properties Test-sua Lai
9/25
Arrow up = laser photon in; Arrow down = Ramanscattering out
8/8/2019 Optical Properties Test-sua Lai
10/25
Elastic scattering:
Rayleigh scattering
Photon in Photon out
No vibration No vibrationIf incident photon energy E; vibration energy v,then
In terms of energy, photon out has energy:
E-vStokes scattering
E+vanti-Stokes scattering
E Rayleigh scattering
8/8/2019 Optical Properties Test-sua Lai
11/25
Selection rule for Raman spectrum
Vibration is active if it has a change in
polarizability, .Polarizability is the ease of distortion of a bond.For Raman-active vibrations, the incident radiationdoes not cause a change in the dipole moment of the
molecule, but instead a change in polarizability.
In starting the vibration going, the electric field ofthe radiation at time t, E, induces a separation ofcharge (i.e. between the nuclear protons and the
bonding electrons). This is called the induced dipolemoment, P. (Dont confuse it with the moleculesdipole moment, or change in dipole moment, becausethis is often zero).
P = E
8/8/2019 Optical Properties Test-sua Lai
12/25
8/8/2019 Optical Properties Test-sua Lai
13/25
8/8/2019 Optical Properties Test-sua Lai
14/25
NMR spectroscopy
NMR is the most powerful tool availablefor organic structure determination.
It is used to study a wide variety ofnuclei:
1H
13C
15N
19F
31 P
8/8/2019 Optical Properties Test-sua Lai
15/25
An electron has a spin quantum number of 1/2 with allowedvalues of +1/2 and -1/2 this spinning charge creates an associated magnetic
field in effect, an electron behaves as if it is a tiny bar
magnet and has what is called a magnetic moment The same effect holds for certain atomic nuclei
any atomic nucleus that has an odd mass number, an oddatomic number, or both also has a spin and a resultingnuclear magnetic moment
the allowed nuclear spin states are determined by thespin quantum number, I, of the nucleus
a nucleus with spin quantum number II has 22II + 1+ 1 spinstates; if I = 1/2, there are two allowed spin states
8/8/2019 Optical Properties Test-sua Lai
16/25
8/8/2019 Optical Properties Test-sua Lai
17/25
Fig. spectrum ofPET
8.16 ppm
4.82 ppm: the ethylenedioxyl
8/8/2019 Optical Properties Test-sua Lai
18/25
Fig. spectrum of
PEA
1.66 ppm (CH2)2-
2.35 ppm: CH2COO
4.26 ppm:the ethylenedioxyl group
8/8/2019 Optical Properties Test-sua Lai
19/25
UV spectroscopyObserved electronic transitions
The lowest energy transition (and most often obs. by UV)
is typically that of an electron in the Highest OccupiedMolecular Orbital (HOMO) to the Lowest UnoccupiedMolecular Orbital (LUMO)
For any bond (pair of electrons) in a molecule, themolecular orbitals are a mixture of the two contributing
atomic orbitals; for every bonding orbital created fromthis mixing (s, p), there is a corresponding anti-bondingorbital of symmetrically higher energy (s*, p*)
The lowest energy occupied orbitals are typically the s;likewise, the corresponding anti-bonding s* orbital is of
the highest energy p-orbitals are of somewhat higher energy, and theircomplementary anti-bonding orbital somewhat lower inenergy than s*.
Unshared pairs lie at the energy of the original atomicorbital, most often this energy is higher than p or s (sinceno bond is formed, there is no benefit in energy)
8/8/2019 Optical Properties Test-sua Lai
20/25
Energy
s*
p
s
p*
n
Atomic orbitalAtomic orbital
Molecular orbitals
Occupied levels
Unoccupied levels
8/8/2019 Optical Properties Test-sua Lai
21/25
Energy
s*
p
s
p*
n
s
s
p
n
n
s*
p*
p*
s*
p*
alkanes
carbonyls
unsaturated cmpds.
O, N, S, halogens
carbonyls
8/8/2019 Optical Properties Test-sua Lai
22/25
In the manufacture of PLED display using a polymer
it can be stimulated luminescence when a suitable
energy level, they will emit color in the energy
received, based on this ability of the polymer
luminescence Scientists have built PLED screen
PLED display (www.oled.at/Oled-tv-the-next-flat-tv-technology.htm)
8/8/2019 Optical Properties Test-sua Lai
23/25
*
*
n
poly(phenylene vinylene)
*
*
n
polyfluorene
**
n
polyfluorene
8/8/2019 Optical Properties Test-sua Lai
24/25
8/8/2019 Optical Properties Test-sua Lai
25/25
X-ray spectroscopyn= 2 dsin
Constructive interference only occurs forcertain s correlating to a (hkl) plane,specifically when the path difference is equalto n wavelengths.