Co-reporter:Di Liu, Ruijuan Yao, Ruizhi Dong, Fengju Jia, Min Fu
Dyes and Pigments 2017 Volume 145(Volume 145) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.dyepig.2017.06.048
•Novel benzothiazole-containing iridium phosphors were developed by attaching substituents at either 5- or 7-site of the ligands.•The emitting color of these phosphors is almost independent of the substituent on these sites.•But F or CF3 always resulted in increased phosphorescence quantum yields and decreased lifetimes in photoluminescence.•The 5-F/CF3-substituted iridium complexes exhibited higher efficiencies than their analogues 7-site isomers in their OLEDs.•The theoretical study reveals that HOMO/LUMO levels were little affected by the substituents at 5- or 7-site of the ligands.A series of bis(2-phenylbenzothiozolato-N,C2′)iridium(acetylacetonate) derivatives are developed for use in phosphorescent organic light-emitting diodes (PhOLEDs). Fluorine (-F), trifluoromethyl (-CF3), N-phenylcarbazole-3-yl (-Cz) and diphenylamino (-Ph2N) are incorporated at the 5- or 7-site of the benzothiazole ring to adjust the properties and performance of the complexes. The emitting colors of these iridium phosphors are almost independent of the substituents and the substitution positions, but -F or -CF3 always resulted in increased phosphorescence quantum yields and decreased lifetimes in photoluminescence. Furthermore, the 5-F/CF3-substituted iridium complexes exhibited higher efficiencies than their analogues 7-site isomers in OLEDs. In particular the device based on 1 exhibits a maximum luminance efficiency of 64 cd A−1 (21.3%). Theoretical calculations were performed to interpret the negligible color tuning effect.Download high-res image (282KB)Download full-size image
Co-reporter:Di Liu, Deli Li, Miao Wang and Wei Li
Journal of Materials Chemistry A 2016 vol. 4(Issue 30) pp:7260-7268
Publication Date(Web):01 Jul 2016
DOI:10.1039/C6TC02217K
Three bipolar host materials, 9-(3′,5′-di(1H-1,2,4-triazol-1-yl)-[1,1′-biphenyl]-3-yl)-9H-carbazole (DTzSCz), 9,9′-(3′,5′-di(1H-1,2,4-triazol-1-yl)-[1,1′-biphenyl]-3,5-diyl)bis(9H-carbazole) (DTzDCz), and 9,9′-(5′-(1H-1,2,4-triazol-1-yl)-[1,1′:3′,1″-terphenyl]-3,3″-diyl)bis(9H-carbazole) (STzDCz), with regular 1,2,4-triazole/carbazole ratios of 2:1, 2:2, and 1:2, are developed for blue and green phosphorescent organic light-emitting diodes (PhOLEDs). Different from the 1,3,5-trissubstituted or 3,4,5-trissubstituted configuration of most 1,2,4-triazole derivatives, here 1,2,4-triazole is placed at the molecular periphery by grafting from its N − 1 atom to the biphenyl bridge without substitution on other atoms. Their thermal, physical and electrochemical properties, and bipolar features are characterized using experimental and theoretical means. The designated structures efficiently suppress the intramolecular charge transfer between donor and acceptor and result in high triplet energies. These materials exhibit excellent performances in sky-blue and green PhOLEDs. For example, when using STzDCz as a host that had a triazole/carbazole molar ratio of 1:2, the blue and green PhOLEDs exhibited maximum external quantum efficiencies ηext of 25.0% and 20.3%, respectively. Moreover, the STzDCz hosted green PhOLED exhibited slow efficiency roll-off with a decrease of only 12.8% relative to the maximum value even at an extremely high brightness of 10000 cd m−2. A triazole/carbazole ratio of 1:2 in the host is proved to be the optimal n-type to p-type ratio favorable for the most balanced charge transportation and highest EL efficiencies.
Co-reporter:Di Liu;Lijun Deng;Wei Li;Ruijuan Yao;Deli Li;Miao Wang ;Shufen Zhang
Advanced Optical Materials 2016 Volume 4( Issue 6) pp:864-870
Publication Date(Web):
DOI:10.1002/adom.201600020
Co-reporter:Di Liu, Ruijuan Yao, Min Fu, Deli Li and Shufen Zhang
RSC Advances 2016 vol. 6(Issue 41) pp:34198-34203
Publication Date(Web):30 Mar 2016
DOI:10.1039/C6RA04551K
Three novel heteroleptic cyclometalated iridium complexes, namely Ir-Cz, Ir-DBF and Ir-Np, were designed and synthesized for use as emitters in organic light-emitting diodes (OLEDs). 2-Phenyl-(aromatic-fused-thiazole) (the aromatic is carbazole, dibenzofuran or naphthalene) was designed as the major cyclometalating ligand framework to enlarge the ligand conjugate length and to study its influence on the photophysical and electrochemical properties and electroluminescent performances of iridium complexes. The three heteroleptic complexes containing acetylacetonate (acac) as an ancillary ligand emit orange to orange-red phosphorescence with a small bathochromic shift in comparison with the reference complex bis(2-phenylbenzothiozolato-N,C2′)iridium(acetylacetonate) [Ir-Bt]. They all exhibited good performance in phosphorescent OLEDs. In particular, a maximum current efficiency of 54 cd A−1, a peak power efficiency of 34 lm W−1 and an external quantum efficiency of 22.2% were realized for Ir-Np based devices.
Co-reporter:Ting Zhang, Di Liu, Yanming Wang, Shikuan Bao, Shufen Zhang
Dyes and Pigments 2015 Volume 122() pp:295-301
Publication Date(Web):November 2015
DOI:10.1016/j.dyepig.2015.07.007
•Dendrimers were synthesized by attaching carbazole dendrons to an oligo-fluorene core.•They have good film-forming ability by solution method.•They were used as non-doped emitter to fabricate organic light-emitting diodes.•The solution-processed devices exhibited pure blue emission with CIE (0.16, 0.08).A group of novel dendrimers containing an oligofluorene core and oligo-carbazole dendrons, were synthesized by a Suzuki cross-coupling reaction. The dendrimers exhibit excellent thermal and amorphous stabilities, and emit deep blue fluorescence with high quantum yields of over 85%. These molecules have non-planar molecular conformations and thus possess excellent solubility and film-forming ability by solution-processing techniques. The dendrimers are used as hole-transporting emitting layers to fabricate organic light-emitting diodes (OLEDs) by a spin coating process. Bright deep blue electroluminescence is obtained with CIE coordinates of ca. (0.16, 0.09), which are quite close to the National Television System Committee (NTSC) standard blue coordinates of (0.14, 0.08). Maximum luminances were in the range of 388–711 cd m−2 and maximum luminance efficiencies were in the range of 0.91–1.07 cd A−1 for the derived devices.Novel carbazole-based dendrimers are developed for use as non-doped emitters in solution-processed organic light-emitting diodes, which exhibit deep-blue electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinate y < 0.1.
Co-reporter:Jinling Cheng
The Journal of Physical Chemistry C 2015 Volume 119(Issue 8) pp:4242-4251
Publication Date(Web):February 4, 2015
DOI:10.1021/jp511578v
Co-reporter:Jinling Cheng, Di Liu and Miao Wang
RSC Advances 2014 vol. 4(Issue 51) pp:27078-27083
Publication Date(Web):27 May 2014
DOI:10.1039/C4RA02746A
The excited-state proton transfer (ESPT) behavior of 4-hydroxybenzoic acid is studied by means of steady-state spectroscopy and theoretical calculations to obtain insight of the excited state dynamics. The large Stokes shift for 4-hydroxybenzoate (4HB) at the pH value of the microenvironment of 6.74 indicates that the ESPT process took place. The proton transfer dynamics of the water-bridged complexes, 4HB·(H2O)x, with two different water chain lengths is investigated using density functional theory and time-dependent density functional theory. The constructed potential energy curves among the optimized 4HB·(H2O)x (enol form) and 4KB·(H2O)x (keto form) geometries at the ground and the first singlet excited state indicate that the ESPT indeed occurs as the barrier is less than 10 kcal mol−1. In addition, the driving force is confirmed by NBO population analysis.
Co-reporter:Jinling Cheng;Dr. Di Liu;Lijun Bao;Kai Xu;Dr. Yang Yang; Keli Han
Chemistry – An Asian Journal 2014 Volume 9( Issue 11) pp:3215-3220
Publication Date(Web):
DOI:10.1002/asia.201402779
Abstract
The synthesis and photophysics of two novel 2-(2′-hydroxyphenyl)benzothiazole (HBT) derivatives are presented. The electron-withdrawing trifluoromethyl (CF3) group in compound 1 facilitates the deprotonation of the phenolic hydroxy group. Well-resolved triple fluorescence from the enol, keto, and phenolic anion, which ranges from 350 to 600 nm, was detected for 1 in ethanol, which marks the first time triple fluorescence from an excited-state intramolecular proton transfer (ESIPT) molecule has been reported. Both triphenylamine and CF3 were introduced into derivative 2. Intramolecular charge transfer and the “red-edge effect” resulted in the bathochromic shift of dual fluorescence of 2. Triple fluorescence was also observed for 2 in ethanol. In mixed acetonitrile and ethanol, pure white-light emission with CIE coordinates of (0.33, 0.33) and a quantum yield of 0.25 was achieved for 2. This work provides a new avenue for the rational design of an ESIPT molecule to achieve white-light generation under mild conditions.
Co-reporter:Di Liu, Huicai Ren, Lijun Deng, and Ting Zhang
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 11) pp:4937
Publication Date(Web):May 20, 2013
DOI:10.1021/am400672y
Four heteroleptic bis-cyclometalated iridium(III) complexes containing 2-aryl-benzothiazole ligands, in which the aryl is dibenzofuran-2-yl [Ir(O-bt)2(acac)], dibenzothiophene-2-yl [Ir(S-bt)2(acac)], dibenzothiophene-S,S-dioxide-2-yl [Ir(SO2-bt)2(acac)] and 4-(diphenylphosphoryl)phenyl [Ir(PO-bt)2(acac)], have been synthesized and characterized for use in organic light-emitting diodes (OLEDs). These complexes emit bright yellow (551 nm) to orange-red (598 nm) phosphorescence at room temperature, the peak wavelengths of which can be finely tuned depending upon the electronic properties of the aryl group in the 2-position of benzothiazole. The strong electron-withdrawing aryls such as dibenzothiophene-S,S-dioxide2-yl and 4-(diphenylphosphoryl)phenyl caused bathochromatic shift of the iridium complex phosphorescence. These iridium complexes were used as doped emitters to fabricate yellow to orange-red OLEDs and good performance was obtained. In particular, a maximum luminance efficiency of 58.4 cd A–1 (corresponding to 30.6 lm W–1 and 19%) with CIE coordinates of (0.45, 0.52) was achieved for Ir(O-bt)2(acac)-based yellow device. Furthermore, the yellow emitting Ir(S-bt)2(acac) was used to fabricate two-element white OLED that exhibited a high efficiency of 32.4 cd A–1 with CIE coordinates of (0.28, 0.44).Keywords: bathochromatic shift; benzothiazole; electrophosphorescence; iridium complex; OLED; yellow;
Co-reporter:Di Liu, Ruixia Yang, Renjie Wang
Dyes and Pigments 2013 Volume 98(Issue 3) pp:317-322
Publication Date(Web):September 2013
DOI:10.1016/j.dyepig.2013.03.025
•The electrophosphorescence of two iridium complexes containing 2-phenylbenzothiazole ligands are studied.•The incorporation of arylamino groups in ligands makes these complexes solution-processible.•High-performance orange and white organic light-emitting diodes were realized with these iridium complexes as doped emitters.The luminescent properties of two cyclometalated iridium complexes containing 2-phenylbenzothiazole ligand were investigated. With diphenylamino groups in the ligands, these iridium complexes can form neat films by spin coating their solutions. It is also possible to prepare their doped films in small molecular host matrix N,N′-dicarbazolyl-4,4′-biphenyl by spin coating. Partially solution-processed organic light-emitting diodes (OLEDs) were fabricated with a luminance efficiency of 20.18 cd A−1 (7.81%), which is even higher than the vacuum-deposited device data for these two complexes, and also better than those for other solution-processed iridium dopant/small molecular host systems. The two-element white OLEDs containing these orange phosphors and traditional blue-emitting iridium in N,N′-dicarbazolyl-4,4′-biphenyl host also exhibited high efficiency of 12.39 cd A−1. It is suggested that the incorporation of the diphenylamino substituents and thus the good hole-injecting and solution processing ability of these iridium complexes are responsible for the good performance.Two iridium complexes decorated by diphenylamino substituents in cyclometalating ligands are suitable for solution processing to fabricate monochromic and white organic light-emitting diodes, which exhibit even better performance than their vacuum-deposited devices or other solution-processed iridium phosphors/small molecular host systems.
Co-reporter:Di Liu, Yong-Heng Duan
Chinese Chemical Letters 2013 Volume 24(Issue 9) pp:809-812
Publication Date(Web):September 2013
DOI:10.1016/j.cclet.2013.05.024
Two novel thieno-[3,4-b]-pyrazine-based molecules, TP-E and TP-O, were designed and synthesized for potential application as red fluorescent emitters. The bulky tetraphenylethylene groups were attached at the periphery of the thieno-[3,4-b]-pyrazine core to form the non-planar molecules, as efficient solid-state emitting materials. The peripheral groups were grafted to the emissive core through either a conjugated acetylene bond, or a non-conjugated ether bond. These molecules exhibit strong red fluorescence in both dilute solutions and in thin films with large Stokes shifts of over 100 nm. The cyclic voltammetry measurements showed the reversible oxidation and reduction behavior for both compounds. All these properties indicate the two compounds are possible functional materials for use in optoelectronic devices.Two novel thieno-[3,4-b]-pyrazine cored molecules with large peripheral arms were synthesized and studied. The photophysical and electrochemical properties indicate their potential application as efficient red fluorescent materials in optoelectronic devices.
Co-reporter:Qing Li, Jiuyan Li, Ruixia Yang, Lijun Deng, Zhanxian Gao, Di Liu
Dyes and Pigments 2012 Volume 92(Issue 1) pp:674-680
Publication Date(Web):January 2012
DOI:10.1016/j.dyepig.2011.05.029
Two novel red-emitting thieno-[3,4-b]-pyrazine-cored molecules with phenyls (TP) or polyphenyls (Müllen type dendron, DTP) as peripheral groups were designed and synthesized. They have large Stokes shifts over 100 nm. DTP is thermally stable with decomposition temperature up to 458 °C. More importantly, it is amorphous with a remarkably high glass transition temperature of 262 °C. DTP can be made into thin films either by solution method or vacuum evaporation. Red OLEDs were fabricated using either spin coated or vacuum evaporated DTP film as emitting layer. The evaporated device exhibited a maximum brightness of 1753 cd m−2 and a luminous efficiency of 0.74 cd A−1, which are among the best data ever reported for thieno-[3,4-b]-pyrazine derivatives so far. In contrary, TP failed to produce satisfied red emission in its evaporated OLEDs.Highlights► We report synthesis and properties of new thieno-[3,4-b]-pyrazine derivative. ► The bulky polyphenyls peripheral groups decorate the planar emissive core to form efficient solid emitters. ► Be suitable for both solution method and vacuum evaporation techniques to fabricate organic light-emitting diodes (OLEDs). ► The performance is the best ever reported for thieno-[3,4-b]-pyrazine derivatives. ► Potential red emitter for application in OLEDs.
Co-reporter:Huicai Ren, Qian Tao, Zhanxian Gao, Di Liu
Dyes and Pigments 2012 Volume 94(Issue 1) pp:136-142
Publication Date(Web):July 2012
DOI:10.1016/j.dyepig.2011.12.005
Two novel spirobifluorene-cored dendrimers containing polyphenylene dendrons with the carbazole (spiro-Cz) and cyano surface groups (spiro-CN) were synthesized and characterized. Both the dendrimers show good solubility in common organic solvents. Spiro-Cz is amorphous even when it is obtained directly from organic solvents and an extremely high glass transition temperature of 332 °C is detected. These dendrimers can be reversibly oxidized and reduced in electrochemical measurements. They are blue fluorescent with small red-shift in solid film absorption and fluorescence spectra. These advantageous merits are suggested to benefit from the combined contribution from the spirobifluorene core and the bulky polyphenylene dendrons. They were used as emitting layer to fabricate organic light-emitting diodes (OLEDs). Deep-blue electroluminescence was obtained for both dendrimers devices.Highlights► We report synthesis and properties of new spirobifluorene-cored dendrimers. ► These dendrimers are amorphous with extremely high glass transition temperature of 332 °C. ► These dendrimers are blue fluorescent with small red-shift in fluorescence spectra of solid films. ► These dendrimers can be reversibly oxidized and reduced. ► These dendrimers exhibit deep-blue electroluminescence in organic light-emitting diodes.
Co-reporter:Qing Li;Jiuyan Li;Huicai Ren;Yongheng Duan;Zhanxian Gao
Macromolecular Rapid Communications 2011 Volume 32( Issue 9-10) pp:736-743
Publication Date(Web):
DOI:10.1002/marc.201100105
Co-reporter:Huicai Ren, Jiuyan Li, Ting Zhang, Renjie Wang, Zhanxian Gao, Di Liu
Dyes and Pigments 2011 Volume 91(Issue 3) pp:298-303
Publication Date(Web):December 2011
DOI:10.1016/j.dyepig.2011.04.008
A group of perylenebisimide-cored dendrimers with polyphenylene dendrons at four bay positions were synthesized and characterized. The electron-deficient pentafluorophenyl or cyano groups were grafted at the dendrimer surface with the aim to further increase the n-type features of the resulted dendrimers. The electrochemical and optical properties were investigated. All the dendrimers show good solubility and film-forming properties, high EA values of 3.8–3.9 eV, and high fluorescent quantum yields. All these merits indicate that they are potential multifunctional materials for application in optoelectronic devices such as solar cells or organic light-emitting devices.Highlights► We report synthesis and properties of new perylenebisimide-cored dendrimers. ► The F- or CN- surface groups increase electron affinity to 3.9 eV. ► Higher generation dendrimers have lower fluorescent quantum yields. ► Potential use as light-harvesting electron acceptors for solar cells. ► Potential use as red emitters in organic light-emitting diodes.
Co-reporter:Qing Li;Jiuyan Li;Yongheng Duan;Zhanxian Gao
Chinese Journal of Chemistry 2011 Volume 29( Issue 12) pp:2655-2658
Publication Date(Web):
DOI:10.1002/cjoc.201100370
Abstract
A new thieno-[3,4-b]-pyrazine-cored dendrimer with polyphenyls dendrons (D2TP) was designed and synthesized for application as red emitter in non-doped organic light-emitting diodes (OLEDs). The bulky dendritic arms enable this molecule to possess significant molecular weight and good solubility in common organic solvents. As a result, D2TP is suitable for solution processing methods such as spin coating to make thin films and devices. In addition, these large dendrons provide site-isolation effect on the planar emissive core to prevent fluorescence quenching or intermolecular interaction. The photophysical and electrochemical properties of D2TP were investigated in its dilute solutions. D2TP was used as non-doped emitter to fabricate OLEDs by spin coating method and saturated red electroluminescence was obtained.
Co-reporter:Huicai Ren, Jiuyan Li, Renjie Wang, Ting Zhang, Zhanxian Gao, Di Liu
Polymer 2011 Volume 52(Issue 16) pp:3639-3646
Publication Date(Web):20 July 2011
DOI:10.1016/j.polymer.2011.06.019
A group of perylene bisimide (PBI) cored dendrimers were designed and synthesized. The polyphenylene dendrons containing carbazole functional groups at periphery were attached to the PBI core with expectation to control the intermolecular interaction and to tune the charge transporting ability of dendrimers. Their photophysical, electrochemical and thermal properties were investigated. The spectral data showed that energy transfer and photoinduced charge transfer coexist between the carbazole peripheries and the PBI core, competing to influence the luminescent properties of these dendrimers. The red OLEDs were fabricated with these dendrimers as non-doped emitting layer by solution method. The dendrimers bearing carbazoles exhibited improved EL performance than those model compounds. The improved charge balance state caused by these carbazole units is suggested to be responsible for the EL performance.Influence of dendrons and carbazole surface groups on the photoluminescent and electroluminescent properties of a group of perylene bisimide-cored dendrimers were investigated.
Co-reporter:Jiuyan Li and Di Liu
Journal of Materials Chemistry A 2009 vol. 19(Issue 41) pp:7584-7591
Publication Date(Web):29 Jun 2009
DOI:10.1039/B901618J
Dendrimers are now an important class of materials for use in organic light-emitting diodes (OLEDs). In this Highlight, we make a brief summary of the recent advances on OLEDs by using dendrimers as active materials. In particular, we will focus on several issues related to both the intrinsic structural features and properties, including dendrimer generation and charge mobility, the site isolation effect and prevention of energy transfer, and the host-free character. The potential applications for white electroluminescence via simple dendrimer blending, and host-free blue phosphorescent dendrimers are discussed. Finally, the strategy for dendrimer synthesis will be also discussed.
Co-reporter:Di Liu, Huicai Ren, Jiuyan Li, Qian Tao, Zhanxian Gao
Chemical Physics Letters 2009 Volume 482(1–3) pp:72-76
Publication Date(Web):6 November 2009
DOI:10.1016/j.cplett.2009.09.077
Abstract
A novel perylene bisimide derivative with fluorinated shell possessing remarkably stable amorphous state, further increased electron affinity, efficient and independent red emission was synthesized and qualified as a potential material for use in organic light-emitting diodes and solar cells.
Co-reporter:Jiuyan Li and Di Liu
Journal of Materials Chemistry A 2009 - vol. 19(Issue 41) pp:NaN7591-7591
Publication Date(Web):2009/06/29
DOI:10.1039/B901618J
Dendrimers are now an important class of materials for use in organic light-emitting diodes (OLEDs). In this Highlight, we make a brief summary of the recent advances on OLEDs by using dendrimers as active materials. In particular, we will focus on several issues related to both the intrinsic structural features and properties, including dendrimer generation and charge mobility, the site isolation effect and prevention of energy transfer, and the host-free character. The potential applications for white electroluminescence via simple dendrimer blending, and host-free blue phosphorescent dendrimers are discussed. Finally, the strategy for dendrimer synthesis will be also discussed.
Co-reporter:Di Liu, Deli Li, Miao Wang and Wei Li
Journal of Materials Chemistry A 2016 - vol. 4(Issue 30) pp:NaN7268-7268
Publication Date(Web):2016/07/01
DOI:10.1039/C6TC02217K
Three bipolar host materials, 9-(3′,5′-di(1H-1,2,4-triazol-1-yl)-[1,1′-biphenyl]-3-yl)-9H-carbazole (DTzSCz), 9,9′-(3′,5′-di(1H-1,2,4-triazol-1-yl)-[1,1′-biphenyl]-3,5-diyl)bis(9H-carbazole) (DTzDCz), and 9,9′-(5′-(1H-1,2,4-triazol-1-yl)-[1,1′:3′,1″-terphenyl]-3,3″-diyl)bis(9H-carbazole) (STzDCz), with regular 1,2,4-triazole/carbazole ratios of 2:1, 2:2, and 1:2, are developed for blue and green phosphorescent organic light-emitting diodes (PhOLEDs). Different from the 1,3,5-trissubstituted or 3,4,5-trissubstituted configuration of most 1,2,4-triazole derivatives, here 1,2,4-triazole is placed at the molecular periphery by grafting from its N − 1 atom to the biphenyl bridge without substitution on other atoms. Their thermal, physical and electrochemical properties, and bipolar features are characterized using experimental and theoretical means. The designated structures efficiently suppress the intramolecular charge transfer between donor and acceptor and result in high triplet energies. These materials exhibit excellent performances in sky-blue and green PhOLEDs. For example, when using STzDCz as a host that had a triazole/carbazole molar ratio of 1:2, the blue and green PhOLEDs exhibited maximum external quantum efficiencies ηext of 25.0% and 20.3%, respectively. Moreover, the STzDCz hosted green PhOLED exhibited slow efficiency roll-off with a decrease of only 12.8% relative to the maximum value even at an extremely high brightness of 10000 cd m−2. A triazole/carbazole ratio of 1:2 in the host is proved to be the optimal n-type to p-type ratio favorable for the most balanced charge transportation and highest EL efficiencies.
![3,3'-(5'-(3-(Pyridin-3-yl)phenyl)-[1,1':3',1''-terphenyl]-3,3''-diyl)dipyridine](http://img.cochemist.com/ccimg/921300/921205-03-0.png)
![3,3'-(5'-(3-(Pyridin-3-yl)phenyl)-[1,1':3',1''-terphenyl]-3,3''-diyl)dipyridine](http://img.cochemist.com/ccimg/921300/921205-03-0_b.png)
