Graduate Research @ USC

Design and Syntheses of Polymeric Materials for
Visible and Near-Infrared Emitting Applications
ET - Förster
S1
S1

T1 5
D2
T1
ET - Dexter 5
D0

S0 S0 7
F2

POLYMER LIGAND Eu+3

Sean Owen Clancy, Ph.D.

All material contained within is copyright © 2006 Sean Owen Clancy
and / or the respective institutions.

Polymeric Energy Transfer Complexes

OC10H21 OC10H21
OC10H21

C10H21O
C10H21O
n C10H21O
n
n

O

L O
Ln
Aryl O
L N Er
Aryl O
N N N N
• PM_aryl:Ln(L)2 Ln
L L
L
N N

• PM_trp:Ln(L)3

• PM_aryl:ErTPP

Loker Hydrocarbon Research Institute and Department of Chemistry University of Southern California

Graduate Research Overview
• Background
• Harper Group Research
• Research Goals and Motivation
• Recent Applications
• Lanthanides
• Ligands
• Color Tuning
• Polymers Photophysics
• Energy Transfer

• Visible Emission Resulting from Energy Transfer from Polymers to Ligands to Europium
• Polymers with Pendant Terpyridines
• Polymers with Pendant β-Diketonates

• Infrared Emission Resulting from Energy Transfer from Polymers to Ligands to Erbium

• Summary

• Future Work


Harper Group Research
• Energy Transfer Studies
• Light Harvesting Dendrimers
• Light Harvesting Polymers
• Polymer Photophysics

• Lanthanide Complexes
• β-Diketonate Ligands
• Dative Bonding Heterocyclic Ligands

• Photonic Materials
• Lanthanide Containing Materials
• Organometallic Systems OC10H21
N N
• PPV Syntheses
N N n
• Polymer Sensors C10H21O
O N
Eu
• Photonic Crystals O N
• Quantum Dots N N
S
• Two-Photon Dyes n N 3

• Loker Hydrocarbon Research Institute and Department of Chemistry University of Southern
California

Research Goals and Motivation
Facilitate Tunability and Processing
• Polymers are easier to process than inorganic systems.
• Polymeric device properties can be altered by changing the chemical structure of the
polymer.

Increase Efficiencies
• Electrical excitation produces 25% singlets and 75% triplets.1
• Polymeric devices typically have higher external quantum efficiencies than small
molecule devices.2,3
• Electrophosphorescent devices have higher efficiencies than electroluminescent
devices.4
• Lanthanides exert the “heavy atom effect,” creating more triplet states,5 which the
lanthanides can harvest and emit as pure colors.
• Improve efficiencies by bringing the donors and acceptors closer to each other.
• Increase dopant/acceptor concentration and prevent aggregation as well.

1. Brown, A. R.; Pichler, K.; Greenham, N. C.; Bradley, D. D.; Friend, R. H.; Holmes, A. B. Chem. Phys. Lett., 1993, 210, 61.
2. Baldo, M. A.; O'Brien, D. F.; Thompson, M. E.; Forrest, S. R. Phys. Rev. B, 1999, 60, 14422.
3. Wilson, J. S.; Dhoot, A. S.; Seeley, A. J. A. B.; Khan, M. S.; Kohler, A.; Friend, R. H. Nature, 2001, 413, 828.
4. Baldo, M.A.; Lamansky, S.; Burrows, P.E.; Thompson, M.E.; Forrest, S.R. Appl. Phys. Lett., 1999, 75, 4.
5. Mukherjee, K. K. R. Fundamentals of Photochemistry, Wiley Eastern Ltd. India, 1992.

California

Background – Recent Applications
• Conjugated polymers have many applications:
• Photovoltaics

Flexible photovoltaic diode
http://www.oc.chalmers.se/science/konjug_polymerer.htm

• OLEDs

20” OLED full color display by IBM 2002. Kodak EasyShare Digital Camera
http://www.zurich.ibm.com/st/display/demo.html Active-matrix OLED
http://www.kodak.com/go/display/


Background – Lanthanides
• Pure color emission (shielded f orbital transitions)
• Robust metals (will not photobleach)
• Induce heavy atom effect (improves rate of intersystem crossing)
• Triplet harvesters
• Reduce polymer degradation

• Eu+3, Sm+3, and Tb+3 can be used in visible devices
• Er+3 can be used in EDFA (1.55 mm)
• Nd+3 and Yb+3 can be used in IR-emitting devices

• Direct excitation is inefficient, to overcome
• Laser source
• Ligands
• Energy transfer is important
• Conjugated organic ligands allow for ET
• Ligands shield lanthanide ion from external environment, such as solvent
(mode of energy loss) and other lanthanide ions (self quenching).


Background – Ligands
• Lanthanides have a high number of coordination sites (from six to twelve).
• Their f orbitals are unable to form hybrid orbitals with ligand.
• Need ligands to bind with more than one coordination site (multidentate).
• Dative bonding ligands, such as terpyridine:

N
N N

• Bidentate ligands, such as beta-diketonates, form both covalent and dative bonds:

O O O OH

R1 R3 R1 R3
R2 R2

California

Background – Color Tuning
• PPV and PPP type polymers are widely used
R R

n n N n
n N n
R R R R
PPP PPV
PF PPy PPyV

• Mechanical properties
- Light weight, easy to process
• Infinite π-system
• Give rise to a band structure
• Band gap varies according to
structure

http://www.tn.utwente.nl/cms/polymers/conj_pol.htm


Background – Polymer Photophysics
Energy level diagram showing modes of
deactivation: e

• a – absorbance
S1 f
• b – fluorescence d

• c – nonradiative decay T1

• d – intersystem crossing
a b c
g
• e – singlet energy transfer
h
• f – triplet energy transfer

• g – phosphorescence
S0
• h – internal crossing


Background – Energy Transfer
Forster Energy Transfer

D* A D A*

• Singlet to singlet
• Coupled dipole-dipole interaction; through space

Dexter Energy Transfer

• Triplet to triplet D* A D A*

• Exchange mechanism; through bond


Background – Energy Transfer
Polymer to Ligand to Lanthanide

E T - F örster
S1
S1

T1 5
D2
T1
E T - D exter 5
D0

S0 S0 7
F2

PO LY M ER L IG A N D Eu+3


Sensitization of Europium Chelates
Design and Synthesis of β-Diketone Ligands

O O

Ar S

BTM DTM 3-PTM 9-PTM

S
Ar =


Ligand Structures
HFA BTM DTM 3-PTM 9-PTM

S
CF3
O O O O O

O O O O O
CF3
S S S S

Asymmetric –
Asymmetric Vs. Symmetric
Extent of Conjugation Length

• Asymmetric ligands perturb the ligand field around a lanthanide.
• The more asymmetric the field, the greater the lanthanide’s emission intensity.
• Shorter effective conjugation length increases the energies of a ligand.
• Larger energy gap will reduce the possibility for back energy transfer.
• Minimizes a pathway for energy loss.


Ligand Syntheses
O O
O O
S
S NaH
O
THF BTM

O O O O

S S NaH S S
O

THF
DTM
O O
O
S

O

S NaH 3-PTM
O
THF

O O
O O
NaH S
S
O
THF
9-PTM


Polymer Structures

Polymer Aryl Group PM_trp
S OC10H21
OC10H21
PM_th

O C10H21O
PM_fu C10H21O
n n

N
PM_py
O

L
N Ln
Aryl O
N
PM_pz L
N N N
Ln
L L
L


Energy Level Tuning of Polyphenylenes – Primary Donors
Br Br Br Br C10H21O OC10H21
i ii
+ (HO)2B B(OH)2
n
COOH OC10H21 C10H21O
O O
O O

PM_es
C10H21O
C10H21O
ii
(HO)2B B(OH)2 + Br Br

OC10H21 n
OC10H21
P1

The synthetic route to PM_es and P1 (i.) ethanol/ PTSA refluxed 24hrs; (ii.) Pd(PPh3)4,
2M Na2CO3, toluene, refluxed 72hrs).

Photophysical properties of P1 and PM_es in THF.
Polymers Abs. Max Emission Singlet Triplet
(nm) energy energy
Max FWHM φFL τ
(eV) (eV)
(nm) (nm) (ns)
P1 350 411 61.5 0.386 0.690 3.24 2.31
PM_es 330 392 61.5 0.662 1.665 3.41 2.47


Synthesis of Polymers with Pendant Terpyridines
Bound to Europium(III) β-Diketonates
PM_trp
OC10H21

C10H21O
n

N

N N
Ln
L L
L


Polymer with Terpyridines Synthesis

OH OC10H21 OC10H21 C10H21O
Br-C10H21 Br2 Br n-Butyllithium
(HO)2B B(OH)2
K2CO3 CH3Cl Br THF
CH3CN OC10H21 OC10H21 B(OMe)3 OC10H21
OH

O O
I2
N +N
N

I-
N


Polymer with Terpyridines Synthesis
Br
O
Br Br + Br Br
Br N N
I-
KOH
CHO NH4OAc
MeOH O
MeOH
N N
N N N
O

OC10H21

OC10H21 Br Br Pd(PPh3)4
C10H21O
(HO)2B B(OH)2 + K2CO3, THF n

C10H21O
N
N
N N
N N
PM_trp


Polymer-Lanthanide Chelate Synthesis

OC10H21 OC10H21

C10H21O C10H21O
n n

N N
N N 3 eq NaOEt, 1 eq LnCl3 N N
Ln
THF
O O
O O
3 eq R1 R2
3
R1 R2


Materials Characterization and Photophysical Performance Data

PM_trp
OC10H21

C10H21O
n

N

N N
Ln
L L
L


Polymer with Terpyridines Characterization
Polymer molecular weights were determined by gel permeation chromatography (GPC)
and multiple angle laser light scattering (MALLS).
Polymer dn/dc (mL/g) Mn (g/mol) Mw (g/mol) PDI
PM_trp 0.1608 8.669 x 106 1.117 x 107 1.29

Photophysical properties of polymers PM_trp in THF.

PM_trp
Absorption maximum 320 nm
Fluorescence maximum 416 nm
FWHM 85 nm
Stokes’ shift 7,212 cm-1
ΦFL 0.062
0.27 ns (0.60)
Lifetime (weighting coefficient)
1.49 ns (0.40)
Singlet energy level (ES) 3.32 eV
Triplet energy level (ET) 2.47 eV
Singlet-triplet gap (∆EST) 0.85 eV


Polymer with Terpyridines Characterization
The absorbance and emission spectra of polymer PM_trp in THF (ex = 320 nm).

1.2

PM_trp abs
1.0 PM_trp ems

0.8
Normalized intensity

0.6

0.4

0.2

0.0

300 350 400 450 500 550 600

Wavelength (nm)


PM_trp:Eu(L)3 Emission Spectra
5
4.0x10
Excited @ Poly Abs Max

PM_trp:Eu(BTM)3
PM_trp:Eu(DTM)3
PM_trp:Eu(3-PTM)3
PM_trp:Eu(9-PTM)3
Intensity (Counts)

5
2.0x10

0.0

325 350 375 400 425 450 475 500 525 550 575 600 625

Wavelength (nm)


PM_trp:Eu(L)3 Emission Maxima
5
4.0x10
PM_trp:Eu(L)3 Emissions, where Ligands:
1 = BTM, 2 = DTM, 3 = 3-PTM, 4 = 9-PTM
5
3.5x10
Residual Emission
Europium Emission
5
3.0x10

5
2.5x10
Intensity

5
2.0x10

5
1.5x10

5
1.0x10

4
5.0x10
1 2 3 4

Ligands


PM_th:Eu(L)2 Ligands Versus Energy Parameters
PM_trp:Ln(L)3 Systems, where Ligands: 1 = BTM, 2 = DTM, 3 = 3-PTM, 4 = 9-PTM.

Emission Intensity ∆S
DScm-1 ∆T
DTcm-1

1.2
Normalized Units

1
0.8
0.6
0.4
0.2
0
1 2 3 4
Ligands
• Smaller distances in singlet energies (∆S) from polymer to polymer-ligand complexes
inversely relate to greater emission intensities from complexes.
• Suggests Forster ET of greater significance than Dexter ET for polymer to ligand ET.


PM_trp:Ln(L)3 Systems, where Ligands: 1 = BTM, 2 = DTM, 3 = 3-PTM, 4 = 9-PTM.

∆EST
DEST

1.05
Normalized Units

1
0.95
0.9
0.85
0.8
0.75
0.7
1 2 3 4
Ligands
• Greater distances in singlet to triplet energies for polymer-ligand complexes almost
directly relate to greater emission intensities from complexes.
• Suggests back energy transfer led to lower emission intensities for DTM and 3-PTM.
• Forward ISC favored by BTM and 9-PTM.


PM_trp:Ln(L)3 Systems Characterization
Photophysical properties of PM_trp gadolinium complexes.
PM_trp: PM_trp: PM_trp: PM_trp: PM_trp:
Gd(HFA)3 Gd(BTM)3 Gd(DTM)3 Gd(3-PTM)3 Gd(9-PTM)3
Abs. Max (nm) 317 358 374 376 358
(cm-1) 31,546 27,933 26,738 26,596 27,933
Em. Max (nm) 400 410 423 429 410
(cm-1) 25,000 24,390 23,641 23,310 24,390
∆ (cm-1) 6,546 3,543 3,097 3,286 3,543
ES (eV) 3.40 3.21 3.09 3.07 3.20
(cm-1) 27,397 25,907 24,938 24,722 25,773
ET (eV) 2.76 2.46 2.43 2.48 2.45
(cm-1) 22,297 19,841 19,608 20,000 19,763
∆EST (eV) 0.64 0.75 0.66 0.59 0.75

Energy transfer efficiencies from PM_trp to L in PM_trp:Eu(L)3 systems, where L =
BTM, DTM, 3-PTM, and 9-PTM.
BTM DTM 3-PTM 9-PTM

PM_trp:Eu(L)3 0.993 0.994 0.991 0.993


PM_trp:Ln(L)3 Systems Characterization
The energy transfer mechanism for the PM_trp:Eu(BTM)3 system.

Energy (eV)

e 3.40

3.21
c
f d
2.64 2.64
2.76 h
h
2.36 2.46 2.36
2.46
a
g
2.14 2.14
b

i

Eu+3 BTM Polymer PM_trp BTM
+3
Eu

FÖRSTER DEXTER
MECHANISM MECHANISM


Synthesis of Polymers with Pendant β-Diketonates
Bound to Europium(III) β-Diketonates
Polymer Aryl Group
S OC10H21

PM_th

O C10H21O

PM_fu n

N
PM_py
O

L
N Ln
Aryl O
PM_pz L
N


Polymers with β-Diketonates Synthesis
Br Br Br Br

PTSA

EtOH

O OH O O

OC10H21
Br Br OC10H21

Pd(PPh3)4, THF
(HO)2B B(OH)2 C10H21O
KCO3 (aq.) n
O O C10H21O
PM_es
O O

OC10H21
OC10H21

NaH
O S C10H21O
C10H21O THF
n n

PM_th O
O O
S
O


Polymer-Lanthanide Chelate Synthesis

OC10H21
OC10H21

C10H21O
C10H21O
n
n
3 eq NaOEt, 1 eq LnCl3
O
THF O

O Ar R1 O Ln
O Ar

O

O O 2
R2
2 eq
R1 R2


Materials Characterization and Photophysical Performance Data

Polymer Aryl Group
S OC10H21

PM_th

O C10H21O

PM_fu n

N
PM_py
O

L
N Ln
Aryl O
PM_pz L
N


Polymers with β-Diketonates Characterization
Polymer molecular weights determined by GPC and MALLS in CHCl3.
Polymer dn/dc Mn Mw DP PDI
mL/g g/mol g/mol
PM_es 0.0975 1.27x104 1.64x104 24 1.28

Photophysical properties polymers with β-diketonate pendant groups.
PM_th PM_fu PM_py PM_pz
Abs. Max (nm) 330 332 330 330
(cm-1) 30,300 30,120 30,300 30,300
Em. Max (nm) 396.5 391 391 396
(cm-1) 25,220 25,575 25,575 25,250
FWHM (nm) 59 54 54.5 58.4
∆ (cm-1) 5,082 4,545 4,728 5,051
QE 0.2121 0.2154 0.1915 0.2134
Life Times (ns) 1.65 1.66 1.52 1.68
kf (s-1) 1.32 x 108 1.32 x 108 1.26 x 108 1.27 x 108
kST (s-1) 4.74 x 108 4.72 x 108 5.31 x 108 4.68 x 108
ES (eV) 3.40 3.40 3.42 3.40
(cm-1) 27,425 27,425 27,585 27,425
ET (eV) 2.50 2.50 2.50 2.47
(cm-1) 20,165 20,165 20,165 19,920
∆EST (eV) 0.90 0.90 0.92 0.93


PM_th:Eu(L)2 Emission Spectra
5
6x10
Excited @ Poly Abs Max

5 PM_th:Eu(BTM)2
5x10
PM_th:Eu(DTM)2
PM_th:Eu(3-PTM)2
PM_th:Eu(9-PTM)2
5
4x10
Intensity (counts)

5
3x10

5
2x10

5
1x10

0
350 375 400 425 450 475 500 525 550 575 600 625 650

Wavelength (nm)

PM_th:Eu(L)2 Emission Maxima
5 PM_th:Eu(L)2 Emissions, where Ligands:
6x10 1 = BTM, 2 = DTM, 3 = 3-PTM, 4 = 9-PTM

Residual Emission
5
5x10 Europium Emission
Intensity (counts)

5
4x10

5
3x10

5
2x10

5
1x10

0
1 2 3 4

Ligand


PM_th:Ln(L)2 Systems, where Ligands: 1 = BTM, 2 = DTM, 3 = 3-PTM, 4 = 9-PTM.

Emission Intensity ∆S
DScm-1 ∆T
DTcm-1

1.2

1
Normalized Units

0.8

0.6

0.4

0.2

0
1 2 3 4
Ligands
• Smaller distances in singlet energies (∆S) from polymer to polymer-ligand complexes
inversely relate to greater emission intensities from complexes.
• Suggests Forster ET of greater significance than Dexter ET for polymer to ligand ET.


PM_th:Ln(L)2 Systems, where Ligands: 1 = BTM, 2 = DTM, 3 = 3-PTM, 4 = 9-PTM.

∆EST
DEST
1.05
Normalized Units

1
0.95
0.9
0.85
0.8
0.75
1 2 3 4
Ligands

• Greater distances in singlet to triplet energies for polymer-ligand complexes almost
directly relate to greater emission intensities from complexes.
• Suggests back energy transfer led to lower emission intensities for DTM and 3-PTM.
• Forward ISC favored for BTM and 9-PTM.


PM_th:Ln(L)2 Systems Characterization
Photophysical properties of PM_th gadolinium complexes.
PM_th: PM_th: PM_th: PM_th: PM_th:
Gd(HFA)2 Gd(BTM)2 Gd(DTM)2 Gd(3-PTM)2 Gd(9-PTM)2
Abs. Max (nm) 331 358 374 378 358
(cm-1) 30,211 27,933 26,738 26,455 27,933
Em. Max (nm) 391 416 421 427 405
(cm-1) 25,575 24,038 23,753 23,419 24,691
∆ (cm-1) 4,636 3,895 2,985 3,036 3,242
ES (eV) 3.42 3.23 3.09 3.06 3.21
(cm-1) 27,548 26,042 24,876 24,691 25,907
ET (eV) 2.75 2.42 2.38 2.40 2.39
(cm-1) 22,148 19,531 19,231 19,380 19,305
∆EST (eV) 0.67 0.81 0.71 0.66 0.82

Energy Transfer Efficiencies from Polymer to Ligand to PM_aryl:Eu(L)2 Systems,
where L = HFA, BTM, DTM, 3-PTM, or 9-PTM.
BTM DTM 3-PTM 9-PTM
PM_fu:Eu(L)2 0.998 0.998 0.998 0.998
PM_py:Eu(L)2 0.999 0.998 0.998 0.998
PM_pz:Eu(L)2 0.998 0.998 0.997 0.998
PM_th:Eu(L)2 0.998 0.998 0.998 0.998


PM_th:Ln(L)2 Systems Characterization
The energy transfer mechanism for the PM_th:Eu(BTM)2 system.
Energy (eV)

e 3.42

3.23
c
f d
2.64 2.64
2.75 h
h
2.36 2.42 2.36
2.42
a
g
2.14 2.14
b

i

Eu+3 BTM Polymer PM_th BTM Eu
+3

FÖRSTER DEXTER
MECHANISM MECHANISM


Conclusions – Europium Sensitization Project
• Energy transfer has been shown to occur from polyphenylenes as the energy donors to
ligand systems as intermediate acceptors and then to lanthanides as the terminal acceptors.

• Higher intensities of emission from lanthanide were due to:
• Ligands that were asymmetric and had shorter effective conjugation lengths.
• Binding acceptor complex directly to donor polymer.
• Pendant β-diketonates bind complex better than terpyridines.
• Better matching of energy levels between ligand systems with lanthanides, as
illustrated by BTM and 9-PTM being brighter than DTM and 3-PTM.
• Smaller relative singlet energy distances between polymer and polymer-ligand
system (favoring Forster ET).
• Larger relative singlet to triplet energy gaps on polymer-ligand systems (favoring
forward ISC).

Applications
• Organic / Polymer Light Emitting Diodes
• Methods of Optimizing O/PLEDs
• Sensors


Sensitization of Erbium Chelates
Synthesis of Polymers with Pendant β-Diketonates
Bound to Erbium(III) meso-Tetraphenylporphyrinate
OC10H21

C10H21O

n

Polymer Aryl Group
S
O
PM_th
Er
Aryl O
O
PM_fu N N

N N N
PM_py

N

PM_pz
N


Erbium Porphyrinate Synthesis
Li CH3
N Si CH3 O O
H3C Li
N Si CH
CH3 3
H3C
N
NH HN N N
DME N

N
Li
O O

O

O Cl
Er
ErCl3

Toluene
N
N N
N

Verified with x-ray crystal.


Polymer Erbium Chelate Synthesis

OC10H21

OC10H21

C10H21O

n
C10H21O

n
O
NaOEt / EtOH
S O
O
THF S
O Er

N N
O

O Cl
N N
Er

N
N N
N


Sensitization of Erbium Chelates
Photophysical Performance Data

OC10H21

C10H21O

n

Polymer Aryl Group
S
O
PM_th
Er
Aryl O
O
PM_fu N N

N N N
PM_py

N
PM_pz
N


Poly:ErTPP Absorbance Spectra
1.8
Cl(DME)ErTPP
PM_th:ErTPP
1.6
PM_fu:ErTPP
PM_py:ErTPP
1.4
PM_pz:ErTPP

1.2

1.0
Absorbance

0.8

0.6

0.4

0.2

0.0

-0.2
300 400 500 600 700

Wavelength (nm)


PM_th:ErTPP Visible Emission
Exciting @ Poly Max, Relative to PM_th and Cl(DME)ErTPP
PM_th - Exc(323)
3.0x10
7 Cl(DME)ErTPP - Exc(323)
PM_th:ErTPP - Exc(323)

7
2.5x10
Intensity (counts)

7
2.0x10

7
1.5x10

7
1.0x10

6
5.0x10

0.0

325 350 375 400 425 450 475 500 525 550

Wavelength (nm)

Poly:ErTPP Infrared Emission
Exciting at Porphyrin Absorbance Maxima
4
4.3x10 Cl(DME)ErTPP - Exc(422)
4
4.2x10 PM_fu:ErTPP - Exc(424)
4
4.1x10 PM_py:ErTPP - Exc(422)
PM_pz:ErTPP - Exc(424)
4
4.0x10
4
3.9x10
Intensity (counts)

4
3.8x10
4
3.7x10
4
3.6x10
4
3.5x10
4
3.4x10
4
3.3x10
4
3.2x10
4
3.1x10
4
3.0x10

1400 1450 1500 1550 1600 1650 1700

Wavelength (nm)

Room temperature IR emission at 10-5 M in degassed, anhydrous THF.


Poly:ErTPP Infrared Emission
Exciting at Polymer Absorbance Maxima
4
5.6x10 PM_fu:ErTPP - Exc(323)
PM_py:ErTPP - Exc(323)
PM_pz:ErTPP - Exc(323)
4
5.4x10
Intensity (counts)

4
5.2x10

4
5.0x10

4
4.8x10

4
4.6x10

1400 1450 1500 1550 1600 1650 1700

Wavelength (nm)

Room temperature IR emission at 10-5 M in degassed, anhydrous THF.


Conclusions – Erbium Sensitization Project

• Energy transfer has been shown to occur from polyphenylenes as the energy donors to a
porphyrin system as an intermediate acceptor and then to erbium as the terminal acceptors.

• Infrared emission from a room temperature solution was shown.

• Intensity of erbium emission indifferent to aryl group identity on beta-diketonate.

• Erbium emission ~33% more intense when excited at porphyrin absorbance max.

• Suggests less than ideal matching of energy levels between polymer and porphyrin ligand.

• Either need to modify polymer to match ligand or modify ligand to match polymer.

• Opportunity to provide higher doping densities when coordinating to polymer.


Summary
• Design and synthesis of polymers with higher singlet and triplet energies.
• Kink introduced with para-meta alternation increased both singlet and triplet
energy levels of polyphenylene polymers.

• Design and synthesis of europium complexes with lower triplet energies.
• Changing the structure of one of the aryl groups on a β-diketonate results in
predictable photophysical changes.
• Shorter conjugation length and higher asymmetry results in higher intensity
of lanthanide emission.

• Higher intensity of lanthanide emission produced though the smaller relative singlet
energy distances between polymer and polymer-ligand system (favoring Forster ET)
and larger relative singlet to triplet energy gaps on polymer-ligand systems (favoring
forward ISC).

• Design and synthesis of polymers with the ability to coordinate to lanthanides.
• Polyphenylene-based polymers with pendant ligand functional groups in the
repeat unit are able to donate energy to lanthanide complexes.
• Europium systems produced visible emission.
• Erbium systems produced infrared emission.


Future Work

Extending this Research
• Isolating the final complexes and characterizing by crystal structures or other means.
• Most likely to include model compounds of dimers or trimers of the monomer
unit.

• Incorporating these materials into devices and analyzing their performance.

• See if Dexter ET becomes favored via electrophosphosphorescence, since more
triplets should be formed.

• IR-emitting displays for reading while wearing night-vision goggles.

• IR-emitting materials for waveguides and other telecommunication devices.

• Polymer-bound iridium systems for LEDs and related devices.

• Sensors for a variety of analytes: biologicals, inorganics, and organics.


Knowledge, Skills, and Abilities
Enhanced or Obtained via this Research
• Design and synthesis of: small molecule organics, organometallic complexes /
coordination complexes, and polymers.

• Characterization of materials through a variety of techniques: NMR, mass spectrometry,
elemental analysis, x-ray crystallography, absorption spectroscopy, fluorescence and
phosphorescence spectroscopy, etc..

• Purification of materials via: column chromatography, preparative thin layer
chromatography, medium pressure chromatography, ambient pressure and vacuum
distillation, reprecipitation, recrystallization, and sublimation.

• Structure-property / structure-function relationship studies.

• Data analysis using a variety of software: Excel, Igor Pro, Origin, PhotoChemCAD, etc..


Acknowledgements

University of Southern California
Research Adviser Harper Research Group
Aaron W. Harper, Ph.D. Patrick J. Case, Ph.D.
Jeremy C. Collette, Ph.D.
Committee Members Michael D. Julian, Ph.D.
William P. Weber, Ph.D. Cory G. Miller, Ph.D.
William H. Steier, Ph.D. Asanga B. Padmaperuma, Ph.D.

Funding was provided by:
• A MURI grant administered by the Air Force Office of Scientific Research
(contract number 413009) and
• A PECASE grant administered by the Army Research Office (contract number
DAAD 19-01-1-0788).
• Harold G. Moulton Fellowship, Benson Endowed Fellowship, USC, and LHI.


Graduate Research @ USC

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