1. A New [5] Helicene Derivative as Novel Emissive Material
for Organic Light-Emitting Diode
Siriporn Kamtonwong , Somboon Sahasithiwat , Waraporn Panchan,
Laongdao Menbangpung, and Thanasat Sooksimuang
National Metal and Materials Technology Center
(MTEC) , Thailand
Thank you chairman for your kind introduction.
Good morning, I would like to thanks organizer for give me a chance to present our work here.
Today I’m gladly present our research on topic of A New penta- Helicene Derivative as Novel Emissive Material for Organic Light-Emitting Diode
Pure and Applied Chemistry International Conference 2013
The Tide Resort, January 25, 2013 1

2. Outline Introduction Experimental Results and discussion Conclusion
I will start my talk with
-Indroduction
-Experimental
-Results and discussion
-and conclusion 2

3. Introduction OLED Device Operation Principle - Light - Light + Cathode
Anode
ETL
HTL
Hole + -
EML
Excitation
Light +
Cathode
EML/ETL -
HTL
Anode
Substrate
Organic light emitting diode or “OLED” is the electronic device that emit light when applied voltage.
The OLED can be used as display or light source.
The basic structure for an OLED consists of four thin film layers deposited on substrate.
1 The first layer is the anode, which is Indium-tin-oxide.
2. The hole transport layer is the second.
3. The third layer is an organic emitter.
4. Lastly, fourth layer is the cathode, which is made of metal.
The substrate is made of either a glass or transparent plastic.
When a voltage is applied across the two inner layers
holes and electrons combine forming excitons.
When an exciton decays, a photon is emitted. The light is created.
OLED displays are a promising new display technology that posses advantage such as
-thinner
-fiexible display
-lower power consumption
- a wider viewing angle
OLED Structure
Basic for light generation via OLED 3

4. Helicenes 3,12-Dimethoxy-7,8-dicyano-[5]helicene (DDH)
[5] Helicene [6] Helicene [7] Helicene
Φf =
3,12-Dimethoxy-7,8-dicyano-[5]helicene (DDH) 2 9 3 4 5 6 8 10 11 12 14 1 7 13
Electron
donating
withdrawing
Under UV
DDH in CHCl3
Helicenes are polycyclic aromatic hydrocarbons (PAHs) containing numbers of benzene ring connected at ortho- position.
Fluorescence quantum yields of them were very low.
Our research, we study a new penta-helicene derivative.
Recently, DDH was reported by our team.
It consists of two electron donating groups, methoxy, and electron withdrawing groups , cyano, in a specific location to allow and enhance electron flow in the molecule which enhances its optical properties.
DDH in CHCl3: Φf = 0.27
S. Sahasithiwat, T. Mophuang, L. Menbangpung, S. Kamtonwong and T. Sooksimuang.
Synthetic Metals 160(2010) 4

5. 3,12-Dimethoxy-[i]furan-1,3-diono-[5]helicene (DFH)
as novel Emissive Material for Organic light-Emitting Diode
 In this work,
we designed a new penta-helicene derivative
which has the electron withdrawing group as furan-diono (anhydrie group).
Synthesis of DFH was easy and very cheap cost.
We will hope that it has good thermal and optical properties. 5

6. Experimental
 The experimental composed of two parts of a new penta-helicene derivative and the fabrication of the OLED. 6 6 6

7. Preparation of DFH we prepare DFH as following,1 2 3
70-80%
75%
70%
we prepare DFH as following,
Diels-Alder cycloaddition between diene and maleic anhydride gave adduct 2, then treated with DDQ gave the partially aromatized product 3 in good yield.
The fully aromatized penta- helicene (DFH) was synthesed by bromination of compound 3 with NBS and follow by dehydrobromination with sodium acetate in acetic acid. 7

8. J-V-L Characteristics
OLED fabrication
Configuration:
ITO/PEDOT:PSS(35nm)/DFH/Ca(10nm)/Al(100nm)
Ca/Al
DFH
J-V-L Characteristics
Measured
PEDOT:PSS
ITO
The OLED with ITO/PEDOT:PSS/DFH/Ca/Al configuration were fabricated.
- The patterned ITO coated- glass slide was cleaned.
Subsequently,
PEDOT:PSS was spin coated onto ITO coated-glass,
then this was baked at 140 oC for 10 min to remove residue water.
-DFH was deposited by thermal evaporation.
- The metal cathode layer was also prepared by thermal evaporation of calcium.
-Finally, Aluminum was coated to protect calcium form moisture and oxygen.
We studied the effect of DFH thickness on characteristic device.
Glass 8

9. Results and discussions9

10. Electron withdrawing group Electron withdrawing group
The optical properties of DFH
UV in CHCl3, λmax : 340, 437, 451 nm
PL, λmax : 535 nm
FWHM : 78 nm
Φf = 0.13
This slide shows the optical properties of DFH solution in chloroform.
- Red line present uv absorption spectra.
And Blue line present photoluminescence spectra.
(UV)
The absorbtion band at three hundred forty nano-meter (340 nm) is associated with Pi to pi star transition.
A broad absorption form four hundred to five hundred nano-meter ( nm) is attributed to the intramolecular charge transfer (ICT).
(PL)
when a dilute solution of DFH in chloroform was excited at three hundred sixty nano-meter (360 nm), photoluminescence exhibited a peak at five hundred and thirty-five nano-meter (535 nm).
A full width at half maximum is seventy-eight nano-meter (78 nm).
And quantum yield is point one three (0.13), measured using harmane and harmine as references.
Under UV
Normalized UV/Vis absorption and fluorescence spectra
of DFH in dilute (3x10-6 M) CHCl3 solution.
DFH in dilute CHCl3 solution. 10
Electron withdrawing group
Electron withdrawing group
Electron donating group
Electron donating group

11. Thermal properties of DFH
DSC: Tm 315 oC
TGA: Td,5 360 oC
The thermal properties of DFH were investigated by DSC and TGA (differential scanning calorimeter) (thermal gravimetric analyzer).
The heating scan of DSC indicated that DFH has a high melting point at three hundred and fifteen degree-Celsius (315 oC).
The TGA thermogram shows that DFH starts to decompose at high temperature about three hundred thirty degree- Celsius( 330 oC).
These thermal properties point out that DFH is very stable at high temperature.
DSC thermogram of DFH
TGA thermogram of DFH 11

12. Energy levels of DFH
Cyclic voltammetric technique
HOMO: Ip = -(E'ox + 4.4) eV (1)
LUMO: Ea= -(E‘red + 4.4) eV (2)
The energy levels was studied by using cyclic voltammetric technique.
HOMO is five point nine electron volt. (5.9 eV)
LUMO is three point six electron volt. (3.6 eV)
And energy band gap is two point three electron volt. (2.3 eV)
The lowest unoccupied molecular obital: (LUMO)
The highest occupied molecular orbital: (HOMO)
Cyclic voltammogram of DFH in 0.1 M Bu4NBF4 in acetonitrile solution performed
in a three-electrode cell (a glassy carbon working, a platinum counter and a Ag/Ag+,
0.1 M AgNO3, non-aqueous reference electrode) at a scan rate of 50 mV/s. 12

13. Structure and energy level diagram of the OLED
ITO/PEDOT:PSS(35nm)/DFH/Ca(10nm)/Al(100nm)
Vacuum Level
HIL
EML
Anode
Cathode h+ e-
ITO
PEDOT:PSS
DFH
Ca(10 nm)/Al (100 nm)
Glass
Light
ITO PEDOT:PSS DFH Ca
-4.9 eV
-5.2 eV
-5.9 eV
-3.6 eV
-2.8 eV
LUMO
This slide shows that structure and energy level diagram of the OLED device.
PEDOT:PSS layer is utilized as a hole injection layer
while DFH acts as an emissive material in this device.
HOMO
Structure of the OLED
Energy level diagram 13

14. Current density-voltage-brightness characteristics of the OLED
ITO/PEDOT:PSS(35nm)/DFH/Ca(10nm)/Al(100nm)
ILV Characteristic of OLED with DFH
We study the electroluminescent characteristic of the OLED.
Example of I-L-V- characteristics of one of the device,
it shows the diode characteristic.
-blue line present current density
-and red line present brightness.
Plots of current density-voltage-brightness characteristic
of ITO/PEDOT:PSS/DFH(80 nm)/Ca/Al device 14

15. ITO/PEDOT:PSS(35nm)/DFH/Ca(10nm)/Al(100nm)
thickness
(nm)
Turn on voltage
(V)
Current Eff.
(cd/A)
Power Eff.
(lm/W)
Max.
Brightness (cd/m2)
CIE
Coordinate
(x,y) 60
3.4
0.16
0.09
696
(0.44,0.58)-(0.46,0.54) 80
4.9
0.33
0.15
881
(0.41,0.55)-(0.46,0.52)
100
4.4
0.30
0.13
760
(0.44,0.53)-(0.47,0.52)
(0.41,0.55)-(0.46,0.52)
CIE Coordinate
increasing applied voltage
OLED
Excimer formation
Green
yellow
5.5 V V V
We vary thickness of DFH layer to optimized the efficiency of device.
The results are shown in the table.
The best device composed of DFH, eighty nano-meter thickness (80 nm), which gave
-turn on voltage is four point nine volt (4.9 V)
-current efficiency is point three three candela per ampar (0.33 cd/A)
-power efficiency is point one five lumen per watt (0.15 lm/w)
-Maximum brightness is eight hundred and eighty-one candela per square meter (881 cd/m2)
We also observe that increasing applied voltages, the emitted light changes from green to yellow color.
The phenomenon implied that DFH molecules tend to undergo an excimer formation at high applied voltages. 15

16. Conclusion Easy to synthesized with good yield Good thermal stability
DFH
Easy to synthesized with good yield
Good thermal stability
Excellent optical properties
In conclusion,
penta-helicene (DFH) is
-easy synthesized with good yield,
-good thermal stability
-excellent optical properties
and DFH was successfully utilized as a new emitter for OLED.
These results have opened new windows for molecular structural design and synthesis of other new penta-helicence derivatives as a new class for small organic emissive material.
It offers longer absorption and fluoresces in the greenish region.
DFH was successfully utilized
as a new emitter for OLED. 16

17. Acknowledgments National Metal and Materials Technology Center (MTEC)
National Science and Technology Development Agency
(NSTDA)
Ministry of Science and Technology (MOST), Thailand
under grant number MT-B-55-POL I
Finally, I would like to thank MTEC, Nstda and Ministry of science and technology
for financial support and facilities.
Facilities = fac-ci-li-ties 17

18. Thank you for your kind attention18

19. 19 19 19

20. The formation of excimer in organic molecule
Excited
monomer
Excimer
Monomer
emission
Ground State
Energy
High
Low
LUMO LUMO
HOMO HOMO
Donor
molecule
Acceptor
Excimer
emission
Light emission from excimer is red shifted
from the excited monomer
Excimer: a single excited molecule can interact with an unexcited neighbor to produce the excited dimer, or excimer 20

21. The multi-layered device
Cathode
EIL
ETL
EML
HTL
HIL
Anode
Light +
Cathode
Anode
EIL
ETL
EML
Excitation
HIL
HTL -
Hole
Light
Fig. Basis for light generation via OLED 21

22. 22 22 22

23. OLED fabrication ITO/PEDOT:PSS/DFH/Ca/Al Configuration:
ITO coated-glass slide was cleaned.
PEDOT:PSS was spin-coated onto ITO substrate.
then it was baked at 140 oC for 10 min.
DFH was deposited by thermal evaporation
onto the PEDOT:PSS coated substrate.
Calcium was evaporated onto the organic layer.
Aluminum was coated onto calcium layer. 23

24. NMR 24

25. FT-IR spectrum
1827, 1762 25

26. Enantiomers Helical structure (M) [5] Helicene (P) [5] Helicene
This slide show the stucture of pentahelicene
Since helicenes are twisted molecules which able to form helical structures.
They generally have two enantiomers.
(M)-isomer for clockwise helix
And (P)-isomer for anticlockwise helix
Especially, Chiral helicenes exhibit large specific rotation and a nonlinear optical property.
(M) [5] Helicene
(P) [5] Helicene
Clockwise helix
Anticlockwise helix 26

27. 3,12-Dimethoxy-7,8-dicyano-[5]helicene (DDH)
under
UV 365 nm
In this work, we interested in the substituted helicene,
3,12-Dimethoxy-7,8-dicyano-pentahelicene (DDH)
Because the direction of electron donating and electro withdrawing group in the molecule
could contribute to give higher efficiency of fluorescence emission.
DDH in CH2Cl2
S. Sahasithiwat, T. Sooksimuang, T. Mophuang, L. Menbangpung and S. Kamtonwong
Synthetic Metals 160(2010) 27

28. OLED displays are a promising new display technology that posses advantage such as
-thinner
-fiexible display
-lower power consumption
- a wider viewing angle
Fig. 3. OLED Research 28 28 28

29. 29 29 29

30. Vacuum Level -2.8 eV -3.6 eV -4.9 eV -5.2 eV -5.9 eV
ITO PEDOT:PSS DFH Ca
-4.9 eV
-5.2 eV
-5.9 eV
-3.6 eV
-2.8 eV

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