SCI
&Organic Electronics
Oligosiloxane Functionalized with Pendant (1,3-Bis(9-carbazolyl)benzene)(mCP)for Solution-Processed Organic Electronics
Dianming Sun,[a]Zhaomin Yang,[a]Zhongjie Ren,*[a]Huihui Li,[a]Martin R.Bryce,*[b]Dongge Ma,[c]and Shouke Yan*[a]
Introduction
Carbazole-based optoelectronic materials continue to attract widespread attention for their hole-transporting properties,good thermal stability and versatile chemical modification.[1–7]Typically,the semiconductor poly(N -vinylcarbazole)(PVK)the good hole-transporting properties of which are attributed to the intra-chain p –p stacking alignment,has been widely used in organic photoconductive materials,[8]as the host material for green OLEDs and blue phosphorescent OLEDs,[9–14]and con-ductance switching materials.[15–18]However,PVK forms exci-plexes and triplet trap states which can quench blue emission
of PhOLEDs and the precise triplet level of PVK is ambigu-ous;[19]moreover,its low-lying HOMO energy level (à5.9eV)and high resistivity lead to a high operating voltage,so it is far from an ideal host material.[20]As a conductance switching ma-terial,PVK has an aliphatic hydrocarbon backbone that exhibits low dimensional stability.For another example,1,3-bis(9-carba-zolyl)benzene (mCP)is one of the major milestones as a small-molecule host of choice for vacuum deposited blue PhO-LEDs.[21,22]mCP has the benefits of a simple molecular structure and a triplet energy of 3.0eV.However,mCP has the draw-backs of low thermal and morphological stability (with a glass transition temperature T g of only 608C)which limit its use in high-performance blue PhOLEDs for real applications and com-mercialization.Thus,it remains a great challenge to develop new materials with high thermal,electrochemical,and mor-phological stability,and good film-forming ability as hosts for PhOLEDs and as active layers in non-volatile memory devices.From this viewpoint,functionalized PVK derivatives show im-proved electron-transporting ability,thermal and morphologi-cal stabilities as compared to PVK,such as poly(N -vinyl-3-(9-phenylfluoren-9-yl)carbazole (PVPFK).[17,23,24]Efforts have also been made to improve the thermal stability of mCP while still maintaining the molecules’desirable optoelectronic proper-ties.[21,25–27]Organic–inorganic hybrid materials are one of the best solutions for ideal host materials because the functionality [a]Dr.D.Sun,Dr.Z.Yang,Dr.Z.Ren,Dr.H.Li,Prof.S.Yan
State Key Laboratory of Chemical Resource Engineering
Beijing University of Chemical Technology,Beijing 100029(P .R.China)E-mail:renzj@https://www.wendangku.net/doc/6f4898688.html,
skyan@https://www.wendangku.net/doc/6f4898688.html, [b]Prof.M.R.Bryce
Department of Chemistry,Durham University,Durham,DH13LE (UK)E-mail:m.r.bryce@https://www.wendangku.net/doc/6f4898688.html, [c]Prof.D.Ma
State Key Laboratory of Polymer Physics and Chemistry
Changchun Institute of Applied Chemistry,Chinese Academy of Sciences Changchun,130022(P .R.
China)
Supporting information for this article is available on the WWW under https://www.wendangku.net/doc/6f4898688.html,/10.1002/chem.201402374.
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Full Paper
DOI:10.1002/chem.201402374
and structural strength are easily achieved by design of the or-ganic and the inorganic parts,respectively.[28–33]For instance, 3,5-di(N-carbazolyl)tetraphenylsilane(SimCP)is a good host for blue PhOLEDs:by linking the bulky triphenylsilyl group to the carbazole moiety in a non-conjugated way,the thermal stabili-ty is improved and steric hindrance favourably affects the mo-lecular packing in the condensed phase.[35,36]
Polysiloxanes are a fascinating class of organosilicon poly-mers with good solubility in common organic solvents,good film-forming ability,fair adhesion to various substrates and ex-cellent resistance to thermal,chemical and irradiation degrada-tion.To improve thermal,electrochemical,and morphological stability and film-forming ability of organic semiconductors,in-corporation of siloxanes into organic molecular structures has been successful.[30]This strategy does not significantly affect the electronic properties of the organic semiconductor units. Strohriegl synthesized a side-chain carbazole polymer with a si-loxane main chain(PSX),which displays better performance than PVK,including greater conformational freedom,good so-lution processability and minimized excimer formation upon photoexcitation.[36]However,this method adopted a common synthetic pathway to post-polymerization functionalization which gave a low content of carbazole groups in the polymer chains,which would not be applicable in high performance conductance switching materials.
Herein,we successfully incorporate1,3-bis(9-carbazolyl)ben-zene(mCP)moieties into oligosiloxane chains as pendant groups to obtain the new mCP modified oligosiloxane (ODCzMSi).ODCzMSi possesses a sufficiently high E T of3.0eV because the silicon-oxygen bond interrupts p-conjugation in the polymer main chain.[37–39]This material discourages self-quenching of triplet excitons by preventing phosphorescent dyes from aggregating.In addition,ODCzMSi possesses a high degradation temperature,excellent film-forming ability and good compatibility with the standard blue phosphorescent emitter FIrpic.An efficient blue PhOLED with a solution-pro-cessed emitting layer of ODCzMSi host and FIrpic(10%by weight)displayed a maximum current efficiency of17.7cd Aà1 (7.7lm Wà1,external quantum efficiency9.2%)at1306cd mà2. Additionally,memory devices using ODCzMSi as the active layer exhibit non-volatile write-once read-many-times(WORM) characteristics with low turn-on threshold voltages.ODCzMSi has,therefore,the very attractive properties of both a solution-processable host for blue PhOLEDs and an active material for memory devices,indicating its considerable versatility in or-ganic electronics.
Results and Discussion
Synthesis and characterization
The synthetic route of ODCzMSi(4)is depicted in Scheme1. The starting material9,9’-(5-bromo-1,3-phenylene)bis(9H-carba-zole)(1)was synthesized by a modified Ullmann condensation of carbazole with1,3,5-tribromobenzene in the presence of copper(I)iodide as a catalyst and18-crown-6as a ligand in o-dichlorobenzene.Transformation of1into the diethoxy-
(methyl)silyl-derivative2was achieved by a Barbier–Grignard reaction with methyldiethyoxylchlorosilane.(3,5-Di(9H-carba-zol-9-yl)phenyl)(methyl)silanediol(3)was obtained by subse-quent acid hydrolysis in dilute THF/HCl solution at08C.The desired oligomer4was easily synthesized from the corre-sponding diethoxy monomer(OEt-Si)and dihydroxy monomer (OH-Si)under tetrabutyl titanate(TBOT)catalysed polyconden-sation as described in the Experimental Section.The end groups were blocked with trimethylchlorosilane to stabilize the resultant oligosiloxane.After completion of the reaction,the solution was simply concentrated and the product4precipitat-ed in methanol as a white powder,which was characterized by 1H,29Si NMR spectroscopies and gel permeation chromatogra-phy(GPC).The weight average molecular weight was deter-mined to be2.13kDa with a narrow polydispersity index of 1.13by GPC in THF using polystyrene as a standard.Product4 is highly soluble in common organic solvents such as chloro-form,tetrahydrofuran,toluene and chlorobenzene.Therefore, it can be easily fabricated into films by solution casting,spin-coating and dipping techniques which are advantageous for organic electronics applications.[40]
Thermal analysis
The thermal properties of OCzMSi were characterized by ther-mal gravimetric analysis(TGA)and differential scanning
calo-
Scheme1.Synthetic route for ODCzMSi(4).
2
rimetry (DSC)under a nitrogen atmosphere and are summar-ized in Table 1.
As shown in Figure 1,the decomposition temperature (T d ),which corresponds to a weight loss of 5%at a heating rate of 108C min à1during TGA,was measured as 5408C for ODCzMSi,which implies that the material has very good thermal stability.Meanwhile,a higher glass transition temperature (T g )of 1428C (compared to 608C for mCP)was determined by DSC during the second heating cycle.In addition,no exothermic crystalli-zation or endothermic melting peaks were observed from 40to 2008C,suggesting that amorphous ODCzMSi should exhibit high morphological stability in a device.The excellent thermal stability of ODCzMSi is ascribed to the oligosiloxane backbone,which should be capable of enduring the inevitable Joule heating that occurs during device operation.
Morphology properties
The film-forming ability,morphological stability of ODCzMSi and its compatibility with the dopant FIrpic were investigated by atomic force microscopy (AFM).As shown in Figure 2a,the AFM image of 10wt %FIrpic doped into ODCzMSi film displays
smooth and homogeneous morphology with a small value of root-mean-square (RMS)roughness of 0.33nm.It is free of par-ticle aggregation or phase separation,suggesting both good film-forming ability and good miscibility with the FIrpic.To fur-ther investigate the thermal stability,the film was then an-nealed at 1408C,which is almost the same temperature as with the corresponding T g of ODCzMSi,for 12h.As shown in Figure 2b,the surface roughness changed a little from 0.33to 0.48nm,however,with increasing time (up to 48h)at the same temperature,no further change can be observed (Fig-ure 2c and d).The excellent stability of the film morphology,which is due to the siloxane backbone,means that films should retain their integrity throughout the fabrication and device-operation processes.
Photophysical properties
UV/Vis absorption,photoluminescence (PL;recorded at room temperature)and phosphorescence spectra (recorded at 77K)of ODCzMSi in dilute dichloromethane solution are presented in Figure 3a.The absorption peaks in the UV/Vis spectrum at around 293nm can be assigned to p !p *transitions of the carbazole moiety and weaker absorption peaks at longer wave-lengths of 326and 339nm are attributed to the n !p *transi-tions of extended conjugation of the carbazole moiety.[25]In addition,a relatively wide energy gap (E g )of 3.56eV is ob-tained from the onset of absorption.The photoluminescence (PL)spectrum of displays intense UV emission peaks at 346and 363nm.The absorption and emission spectra of ODCzMSi are nearly identical to those previously reported for phenylcar-bazole structure and mCP ,[38,39,41–43]suggesting that the oligosi-loxane backbone does not significantly influence the photo-physical properties of the organic chromophore.The phos-phorescence spectrum in a frozen dichloromethane solution at 77K revealed a well-structured band in the region of 400–500nm.An E T of 3.0eV was calculated from the highest energy vibronic sub-band of the phosphorescence
spectrum;
Figure 1.a)TGA trace of ODCzMSi recorded at a heating rate of 108C min à1.b)DSC measurement recorded at a heating rate of 108C min à1
.
Figure 2.AFM topographical images of the solution-processed films of ODCzMSi doped with 10%FIrpic:a)unannealed,b)annealed at 1408C for 12h,c)annealed at 1408C for 24h,and d)annealed at 1408C for 48h.
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this is the same value as mCP and is consistent with the dis-ruption of p conjugation caused by the silicon àoxygen bond between the mCP groups.Electrochemical analysis
The electrochemical behaviour of ODCzMSi was investigated by cyclic voltammetry (CV)using tetra(n -butyl)ammonium hex-afluorophosphate (0.1m )as a supporting electrolyte in anhy-drous acetonitrile under a nitrogen atmosphere.In Figure 3b,the CV shows an irreversible oxidation feature similar to those of other carbazole derivatives with unprotected 3,6-posi-tions.[16,28]The highest occupied molecular orbital (HOMO)energy level of ODCzMSi was calculated according to the for-mula E HOMO =à(4.8+E on ox àE Fc )eV.
[29]
The lowest unoccupied mo-lecular orbital (LUMO)energy level was obtained by adding the optical E g to the HOMO level (as shown in Table 1).The HOMO level of ODCzMSi is à5.65eV,which is very similar to that of mCP and 4,4’-N,N ’-dicarbazolylbiphenyl (CBP).[44]This in-dicates that the HOMO of ODCzMSi is mainly located at the electron-rich carbazole units.Quantum chemical calculations on a dimer model of ODCzMSi at the B3LYP/6-31G*level gave the contour plots depicted in Figure 4.The HOMO is localized on the carbazole group,while the LUMO is mainly localized on the phenyl group attached to the carbazole.There is no fron-tier molecular orbital distribution on the silicon àoxygen bond.All the above data establish that the presence of the siloxane chain has a negligible effect on the electronic transition ener-gies and energy levels of the mCP units,thus maintaining the desirable properties of mCP while significantly enhancing the thermal and morphological stability of the material.Blue phosphorescent organic light emitting diode
To evaluate the ability of ODCzMSi to act as a host material for solution-processed blue PhOLEDs,we chose FIrpic (E T 2.6eV)[45]as the standard blue phosphor.Devices were fabricated with the following configuration:indium tin oxide (ITO)/PEDOT:PSS (40nm)/host/10wt %FIrpic (40nm)/1,3,5-tri(m -pyrid-3-yl-phe-nyl)benzene (Tm3PyPB,5nm)/1,3,5-tris(1-phenyl-1H -benzimida-zol-2-yl)benzene (TPBi,30nm)/LiF (1nm)/Al (100nm).In this architecture,PEDOT:PSS acts as a hole-injection layer,the host doped with 10wt %FIrpic is spin-coated to form an emitting layer,and Tm3PyPB [46]and TPBi function as the hole/exciton-blocking and electron transporting layers,respectively.The rel-ative energy levels of each layer are presented in Figure 5a.The E T values of ODCzMSi and Tm3PyPB are sufficiently high to prevent luminescence quenching by the carrier transport layer and to confine triplet excitons in the emitting layer.As shown in Figure S1in the Supporting Information,the electrolumines-cent (EL)spectra of the blue PhOLED shows emission exclu-sively from FIrpic (l max =472nm),without any contribution from ODCzMSi.This indicates that reverse transfer of triplet ex-citons from phosphor to host is prevented in this device.Im-portantly,a stable emission spectrum is observed throughout the operating voltage (6–10V).The intensity of the emission shoulder around 500nm increases when the charge recombi-nation zone shifts to the side of the hole-transporting layer.As the operating voltage increased,the intensity of this shoulder is enhanced,which indicates that the emission zone is shifted away from the electron-transporting layer because of the im-proved electron flow.
It is notable that the highest external quantum efficiency for the device is 9.2%as shown in Figure 5c.Power and current efficiencies plotted with respect to current density are depict-ed in Figure 5d,and all the device data are summarized in Table 2.The device shows a current efficiency of 17.7cd A à1and maximum power efficiency of 7.7lm W à1,which are ob-served over a wide range of high luminance.The overall per-formance of this device is excellent and is competitive with the best blue PhOLEDs using solution processed host materi-als.[47,48]The efficiency is considerably enhanced compared to analogous optimized FIrpic devices with PVK as the host,which gave maximum values of 1640cd m à2; 6.3cd A à1;3.3lm W à1;h ext 3.3%.
[14]Figure 3.a)Absorption,photoluminescence (at room temperature)and
phosphorescence spectra (at 77K)of ODCzMSi in dichloromethane.b)Cyclic voltammogram of ODCzMSi in CH 2Cl 2for oxidation
scan.
Figure 4.Calculated spatial distributions of the HOMO and LUMO energy densities of ODCzMSi.
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To further verify the exciton confinement property of the host,transient photoluminescence decays were measured at a wavelength of 475nm for a thin film (formed on quartz sub-strates)with 10wt %FIrpic dispersed in ODCzMSi.As shown in Figure 6,the emission displays nearly mono-exponential decay curves,indicating that the triplet energy transfer from FIrpic to ODCzMSi is completely suppressed and the energy is well con-fined in the emission layer.Meanwhile,the decay curve of the corresponding film annealed at 1408C for 24h was essentially unchanged which is consistent with high thermal stability of the FIrpic-ODCzMSi film.Memory device characteristics
To investigate the applicability of ODCzMSi in non-volatile memory devices,we fabricated a sandwich device with a con-figuration of ITO/ODCzMSi/Au.Figure 7shows the typical cur-rent density–voltage (J –V )characteristics and stability tests of this device.As depicted in Figure 7a,the device could be switched on when a negative voltage sweep (with ITO as cath-ode and Au as anode)was ap-plied.Initially a low-conductivity (OFF)state (current density level ~10à6mA cm à2)was observed.As the negative bias increased,a sharp transition from the low-conductivity (OFF)state to a high-conductivity (ON)state was observed at à0.91V (the switch-ON voltage),as indicated by the abrupt increase in the current density (sweep 1).For a memory device,this transition from the OFF-to the ON-state could serve as the “writing”pro-cess for practical data storage applications.Once the device has reached its ON-state,it could retain its ON-state when the voltage sweep was repeated from 0to à3V (sweep 2).Even when the power was shut off or during the reverse voltage sweep (sweep 3),the ON-state was still retained (sweeps 4and
5),meeting the features of a WORM (write-once-read-many-times)device.Further experiments on duplicated devices re-vealed that the J –V characteristics were repeatable with good accuracy,and device degradation was not observed.Further-more,the almost linear current–area dependence of both the OFF-and ON-states when the active device area was reduced (Au electrode)—giving almost constant current densities—indi-cates the absence of sample degradation and dielectric break-down.The observed conductance switching can thus be fully attributed to the change in the material properties of the ODCzMSi layer upon applying an external bias.It is noteworthy that the on-switching voltage was only à0.91V which
facilities Figure 5.a)Relative energy levels of the materials used in the 10wt %FIrpic-doped PhOLED;b)J –V –L characteris-tics;c)external quantum efficiency versus current density;d)power efficiency and current efficiency versus cur-rent
density.
Figure 6.Transient photoluminescence decay (excited at 343nm)curves at room temperature monitored at 475nm for the unannealed 10wt %FIrpic co-deposited with ODCzMSi,and the corresponding film annealed at 1408C for 24h.
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low-power consumption.The electrical stability performance was also carried out for the memory device under ambient air conditions.Figure 7b shows the retention time test under a constant voltage for the OFF-and ON-states.Under a con-stant bias of à0.5V,no significant degradation in current is ob-served for both the ON-and OFF-states with longer operating time (8000s);the device maintained an ON/OFF current ratio of about 2.5 103.Moreover,this non-volatile irreversible elec-trical switching behaviour was also observed when scanning the device first with positive bias (with ITO as anode and Au as cathode),indicating its independence on the voltage polarity.However,the switching voltage is slightly increased to around 1.26V and the ON/OFF current density ratio is reduced to about 300,as shown in Figure 7c and d.
Conformation induced electrical switching mechanism can satisfactorily explain the electrical switching behaviour of
ODCzMSi.There are literature precedents for the electrical bist-ability of some non-conjugated polymers with pendant active groups.[49–51]
For example,memory effects of PVK derivatives with flexible spacers between the carbazole pendant group and the polymer backbone,[16,17]
in which regio-random and
regio-regular alignments correspond to the low-and high-con-ductivity states,showed only WORM or volatile features.Simi-larly,different stable conformations of ODCzMSi with high or
low conductivity states could be obtained under the action of electric field through the p –p stacking alignment of its pend-ent aromatic groups inducing the electrical switching per-formance.The proposed mechanism of conformation change is sup-ported by annealing the ITO/ODCzMSi/Au device with high-conductivity states.The regular p –p stacking conformation of the high-conductivity states should be converted into a disor-dered state by thermal annealing.Thus,we chose 1408C,which is close to the T g of ODCzMSi where its chain segments should have higher flexibility.When the device with high-con-ductivity states was annealed at 1408C for 12h,the previous sustained high-conductivity (ON)state disappeared as shown in Figure 8.Instead its initial low-conductivity (OFF)state from 0V to à1.01/1.59V is observed,and then there is a sharp in-crease,indicating another transition of the device from the low-conductivity to a high-conductivity state.Once the an-nealed device is switched on,it remains there and cannot be returned to its initial low conductivity state.This suggests that the stored data can be erased by thermal treatment.The rever-sibility of the process confirms the proposed conformation change mechanism.In addition,comparing this non-volatile elec-trical switching behaviour of the annealed device with that of the non-written device,some differ-ence was observed.With a nega-tive bias sweep,the switching voltage is slightly increased to around à1.01V and the ON/OFF current density ratio is increased to about 7 103as shown in Fig-ure 8a and b.With a positive bias sweep,the switching volt-age is slightly increased to around 1.59V and the ON/OFF current density ratio is almost the same as shown in Figure 8c and d.The different switching voltages and ON/OFF current density ratios may be attributed
to the different initial states of the annealed device and the non-written device,which have different regio-regularity of the PDCzMSi chains.
Conclusion
In summary,a solution-processable oligosiloxane derivative has
been designed and synthesized by attaching the mCP moiety to the oligosiloxane https://www.wendangku.net/doc/6f4898688.html,pared to mCP ,ODCzMSi
exhibits excellent thermal and morphological stability.Because the mCP segments are connected through silicon àoxygen bonds that disrupt the p conjugation,ODCzMSi maintains a high E T of 3.0eV.A highly efficient blue PhOLED with maxi-mum external quantum,current and power efficiencies of 9.2%,17.7cd A à1,and 7.7lm W à1,respectively,was fabricated
using ODCzMSi as the host material and FIrpic as the triplet
emitter.Moreover,memory devices using PDCzMSi as an active layer exhibited non-volatile memory performance with high
stability in retention time up to 8000s and low switch on
volt-Figure 7.Typical J –V curves of the ITO/ODCzMSi/Au memory device.The sweep sequence and direction are indi-cated by the number and arrow,respectively.a)Sweep numbers 1,2,4:0to à3V;sweep numbers 3,5:0to
+3V;c)sweep numbers 1,2,4:0to +3V;sweep numbers 3,5:0to à3V.The effect of operation time on the
current density of the device at the ON-and OFF-states tested at different biases under ambient conditions:b)à0.5V;d)0.5V.
6
age.These results demonstrate the great promise and versatili-ty of organic–inorganic hybrid materials for organic electronics applications.Experimental Section
Materials
The intermediate methyldiethyoxylchlorosilane was prepared ac-cording to our previous report.[52]All reactants (Adamas-beta)were
purchased from Adamas Reagent,Ltd.without further purification,and all solvents were supplied by Beijing Chemical Reagent Co.,Ltd.Anhydrous and deoxygenated solvents were obtained by dis-tillation over sodium benzophenone complex.
Molecular simulation
The geometrical and electronic calculations were carried out on the dimer of PDCzMSi with the Gaussian 09program package.[53]The molecular orbitals were calculated by the density functional theory (DFT)method at the B3LYP level with the 6–31G(d)atomic basis set.
Device fabrication PhOLEDs
The configuration used is:indium tin oxide (ITO)/PEDOT/PSS (40nm)/ODCzMSi/10wt %FIrpic (40nm)/1,3,5-tri(m -pyrid-3-yl-phe-nyl)benzene (Tm3PyPB,5nm)/1,3,5-tris(1-phenyl-1H -benzimidazol-2-yl)benzene (TPBi,30nm)/LiF (1nm)/Al (100nm).The hole-injec-tion material PEDOT/PSS,and elec-tron-transporting and hole-block-ing material TPBi,were used from commercial sources.ITO-coated glass with a sheet resistance of 10W square à1was used as the substrate.Before device fabrica-tion,the ITO-coated glass substrate was pre-cleaned carefully and ex-posed to UV-ozone for 2min.After that,PEDOT/PSS was spin-coated onto the clean ITO substrate as a hole-injection layer.Then,the host ODCzMSi doped with 10%(by weight)FIrpic was spin-coated to form a 40nm thick emissive layer (EML)and annealed at 1008C for 30min to remove residual sol-vent.Finally a 5nm thick hole-blocking layer (HBL)of Tm3PyPB and a 30nm-thick electron-trans-porting layer (ETL)of TPBi were vacuum deposited,and for the cathode of a 1nm thick layer of lithium fluoride (LiF)and aluminum (100nm)were sequentially depos-ited onto the substrate through shadow masking with a pressure of 10à6Torr.The current density–voltage–luminance (J –V –L )charac-teristics of the device was mea-sured using a Keithley 2400Source
meter and a Keithley 2000Source
multimeter equipped with a calibrated Si-photodiode in a glove
box.The EL spectra were measured using a JY SPEX CCD 3000spectrometer.The EQE values were calculated from the luminance,
current density,and electroluminescence spectrum according to previously reported methods.[54]All measurements were performed at room temperature under ambient conditions.Memory device
The memory devices with the configuration of ITO/ODCzMSi/Au were fabricated as follows.ITO-coated glass with a sheet resistance of 10W square à1was used as the substrate.Before device fabrica-tion,the ITO-coated glass substrate was pre-cleaned carefully.After that ODCzMSi was spin-coated onto the ITO glass substrate.Finally,an Au top electrode was sputter coated onto the active layers through a shadow mask at a system pressure of 10à3bar.The cur-rent density–voltage (J –V )characteristics of the sandwich devices were recorded with a Keithley 4200SCS semiconductor parameter analyser (Keithley,Cleveland,OH)equipped with a Micromanipula-tor 6150probe station in a clean and metallically shielded box in an ambient environment.
Characterization
1
H and 13C NMR spectra were recorded on a Bruker AV400(400MHz )spectrometer.Chemical shifts (d )are given in parts per million (ppm)relative to tetramethylsilane (TMS;d =0)as the inter-nal reference.1H NMR spectral data are reported as chemical shift,relative integral,multiplicity (s =singlet,d =doublet,m =multiplet),coupling constant (J in Hz)and assignment.Elemental analyses of carbon,hydrogen,and nitrogen were performed on a Vario
EL
Figure 8.The ITO/ODCzMSi/Au memory device in its high-conductivity states is annealed at 1408C for 12h and
then the device properties are determined again.Typical J –V curves of the annealed memory device,the sweep
sequence and direction are indicated by the number and arrow,respectively.a)Sweep numbers 1,2,4:0to à3V;
sweep numbers 3,5:0to +3V;c)sweep numbers 1,2,4:0to +3V;sweep numbers 3,5:0to à3V.The effect
of operation time on the current density of the device at the ON-and OFF-states tested at different biases under ambient conditions:b)à0.5V;d)0.5V.7
cube.UV/Vis absorption spectra were recorded on a Shimadzu UV-3600spectrophotometer.PL spectra were recorded on a Hitachi F-7000fluorescence spectrophotometer.Differential scanning calo-rimetry(DSC)was performed on a TA Q2000Differential Scanning Calorimeter at a heating rate of108C minà1from25to2008C under nitrogen atmosphere.The glass transition temperature(T g) was determined from the second heating scan.Thermogravimetric analysis(TGA)was undertaken with a METTLER TOLEDO TGA/DSC 1/1100SF instrument.The thermal stability of the samples under a nitrogen atmosphere was determined by measuring their weight loss while heating at a rate of108C minà1from25to8008C.Cyclic voltammetry(CV)was carried out in nitrogen-purged dichlorome-thane(oxidation scan)at room temperature with a CHI voltammet-ric analyser.Tetrabutylammonium hexafluorophosphate(TBAPF6;
0.1m)was used as the supporting electrolyte.The conventional three-electrode configuration consists of a glassy carbon working electrode,a platinum wire auxiliary electrode,and an Ag/AgNO3 pseudo-reference electrode with ferrocenium–ferrocene(Fc+/Fc)as the internal standard.Cyclic voltammograms were obtained at scan rate of100mV sà1.The onset potential was determined from the intersection of two tangents drawn at the rising and back-ground current of the cyclic voltammogram.Gel permeation chro-matography(GPC)analysis was carried out on a Waters515-2410 system using polystyrene standards as molecular weight references and tetrahydrofuran(THF)as the eluent.The morphologies and thickness of the oligomer films coated on the ITO substrate were measured using atomic force microscopy(Agilent-5500AFM) under tapping mode.
Synthetic procedures
9,9’-(5-Bromo-1,3-phenylene)bis(9H-carbazole)
A mixture of carbazole(16.7g,100mmol),1,3,5-tribromobenzene
(15.7g,50mmol),CuI(0.95g,5mmol),18-crown-6(2.0g, 7.5mmol),potassium carbonate(36.6g,150mmol),and o-dichlor-obenzene(200mL)was de-gassed and stirred at1808C for24h under argon.After cooling to room temperature,the mixture was quenched with saturated(NH4)2CO3solution and extracted with chloroform;the combined organic layer was washed with distilled water three times and dried over anhydrous magnesium sulfate. Then the solvent was evaporated in vacuum to give the crude product,which was purified by column chromatography on silica gel using(petroleum ether/dichloromethane=60:1v/v)as the eluent to obtain the product as a white solid(11.9g,49%).1H NMR (400MHz,[D8]THF):d=7.36(t,J=7Hz,4H;Ar H),7.49(t,J=7Hz, 4H;Ar H),7.57(d,J=8Hz,4H;Ar H),7.82(s,1H;Ar H),7.89(s, 2H;Ar H),8.17ppm(d,J=8Hz,4H;Ar H);13C NMR(400MHz, [D8]THF):d=109.54,120.47,123.81,124.23,126.12,128.72, 140.43ppm.
9,9’-(5-(Diethoxy(methyl)silyl)-1,3-phenylene)bis(9H-carbazole) Under an argon atmosphere,chlorodiethoxy(methyl)silane(2.5mL, 20mmol)and magnesium powder(0.24g,10mmol)were added in anhydrous THF(30mL).The reaction flask was heated to708C and a solution of9,9’-(5-bromo-1,3-phenylene)bis(9H-carbazole) (4.87g,10mmol)in THF(50mL)was added drop-wise during 30min.After the addition was completed,the mixture was stirred for3h at this temperature.The mixture was then cooled to room temperature and extracted with Et2O.The solvent was evaporated in vacuo to give the crude product,which was purified by column chromatography on silica gel using(petroleum ether:dichlorome-thane=6:1v/v)as the eluent to obtain the product as a colourless
oil(3.46g,64%).1H NMR(400MHz,[D8]THF):d=0.37(s,3H,-CH3),
1.73(t,J=7Hz,6H;-OCH2CH3),3.84(q,J=7Hz,4H;-OCH2),7.25
(t,J=8Hz,4H;Ar H),7.42(t,4H;Ar H),7.56(d,J=8Hz,4H;Ar H),
7.95(s,1H;Ar H),8.0(s,2H;Ar H),8.14ppm(d,J=8Hz,4H;Ar
H);13C NMR(400MHz,[D8]THF):d=à8.10,16.01,56.62,107.62,
118.23,121.81,124.06,129.08,137.22,138.26,138.84ppm;
29Si NMR(400MHz,[D
8
]THF):d=à22.17ppm;elemental analysis calcd for C35H32N2O2Si:C77.74,H5.96,N5.18;found:C77.78,H
5.91,N5.20.
ODCzMSi
To a mixture of9,9’-(5-(diethoxy(methyl)silyl)-1,3-phenylene)bis(9H-carbazole)(1.08g,2mmol)and THF(100mL),water(2mL)and 1m HCl(2drops)was added.The mixture was stirred at08C for 24h.After the reaction was complete,the mixture was extracted with Et2O and washed with distilled water three times and dried over anhydrous magnesium sulfate.The filtrate was concentrated by reduced pressure to give OH-Si monomer to which was added
a solution of9,9’-(5-(diethoxy(methyl)silyl)-1,3-phenylene)bis(9H-
carbazole)(1.08g,2.0mmol)in THF(50mL)and tetra-n-butyl tita-nate(2drops)as catalyst.The mixture was stirred at808C for 5days while tracking the progress of the reaction with a Fourier transform infrared(FTIR)spectrometer.After the reaction was com-plete,trimethylchlorosilane(0.5mL)was added and stirred for an-other12h.Afterwards,the solvent was evaporated in vacuum to give a sticky liquid,which was dissolved in toluene and precipitat-ed with methanol to obtain the product as white powder.1H NMR (400MHz,CDCl3):d=7.02–7.52(m,13H;ArH),7.71–8.23(m,6H;
ArH),0.33ppm(s,3H;-CH3);GPC(RI,polystyrene calibration) M w=2.13 103,M w/M n=1.13.
Acknowledgements
The financial supports of NSFC(21104002&51221002)and Bei-jing Higher Education Young Elite Teacher Project(YETP0491) and the CHEMCLOUDCOMPUTING of the Beijing University of Chemical Technology are gratefully acknowledged.Z.R.thanks the China Scholarship Council for funding a visit to Durham University.
Keywords:OLEDs·organic electronics·organic–inorganic hybrid composites·polymers·worm memory device
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Received:February26,2014
Revised:August27,2014
Published online on&&&&,0000
9
FULL PAPER
&Organic Electronics
D.Sun,Z.Yang,Z.Ren,*H.Li, M.R.Bryce,*D.Ma,S.Yan*
&&–
&&
Oligosiloxane Functionalized with Pendant(1,3-Bis(9-carbazolyl)benzene) (mCP)for Solution-Processed Organic
Electronics
Won’t forget:Oligosiloxane(ODCzMSi)
functionalized with mCP has been syn-
thesized and shown to have outstand-
ing properties for solution-processed
electronics applications.The hybrid ma-
terial has high thermal and morphologi-
cal stability and high triplet energy.A
phosphorescent OLED with an emissive
layer of ODCzMSi–FIrpic shows very
high efficiency blue emission.Efficient
memory devices using ODCzMSi as the
active layer have also been demonstrat-
ed.
10