Transaction of the Materials Research Society of Japan
34[1] 141-144 (2009)
Syntheses and Photonic Properties of Indolocarbazole Derivatives
1
Masaji Akimoto1, Tatsuya Kawano2, Yu Nagase1,2*, Masuki Kawamoto3, Tatsuo Wada3
Graduate School of Technology and Science, 2Department of Applied Chemistry, Graduate School of Engineering, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa, 259-1292, Japan, 3 Riken, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan *Tel: +81-463-58-1211, Fax: +81-463-51-2012, E-mail:
[email protected] In this study, the syntheses of indolo[3,2-b]carbazole (INC) derivatives have been investigated, which possessed the planer and conjugated structure and showed the strong blue fluorescence by the irradiation of UV light. In order to improve the solubility of INC, N-alkylated INC derivatives were prepared by the reaction of INC with NaH followed by the addition of alkyl halides, the carbon numbers of which were C1 - C10. The obtained alkylated INCs were soluble in some solvents, and the unique thermal properties were observed for the alkylated INCs with a long alkyl chain, which became amorphous after melting and showed the mesomorphic-like transitions. According to the fluorescence spectroscopy, these alkylated INC derivatives exhibited the strong emission, the quantum yield of which was about 0.50. On the other hand, the INC derivative containing an octyl group and a p-vinylbenzyl group at N-positions was prepared as a monomer compound to obtain polystyrenetype polymer with INC moiety by a radical polymerization. It was found that the polymer was a glassy polymer and the coating film was easily prepared. In addition, the obtained polymer exhibited a high thermal stability, which maintained the high emission property of INC moiety. Key words: Indolocarbazole / N-alkylation / Polymer containing indolocarbazole / Photoluminescence 2. RESULTS AND DISCUSSION 2.1 Preparation of N-alkylated INC The starting INC was prepared according to the literature [6], via a cyclization reaction of di(1H-indol-3yl)methane (DIM) obtained from indole and formaldehyde by Mannich reaction. Then, N-alkylated INC was prepared by a substitution reaction between various alkyl iodides and INC anion derived from the reaction of INC with sodium hydride in DMF, as shown in Scheme 1. The different kinds of alkyl groups were introduced into N-position of INC, the carbon numbers of which were C1 to C10 (methyl to decyl groups). m of the sample code, INC-Cm, means the carbon number of alkyl chain. The obtained N-alkylated INCs were soluble in some solvents, such as chloroform, tetrahydrofuran and ethyl acetate, in the case of the long alkyl chain more than C6. Therefore, the improvement of solubility of INC by introduction the long alkyl chain was succeeded. Moreover, the melting points of N-alkylated INC were markedly decreased in the case of long alkyl chain more than C6, which was related to the solubility test. Therefore, it was considered that the intermolecular interaction of INC derived from the planer structure was decreased by the introduction of the long alkyl chain at Nposition. The melting temperatures of N-alkylated INC decreased between 298℃ and 100℃ as the alkyl chain length increased from C1 to C10. Interestingly, the unique thermal properties were observed for the alkylated INCs with the longer alkyl chain more than C6, which became amorphous after melting and showed the mesomorphic-like transitions. The detailed investigations of these phase transitions were now in progress.
1. INTRODUCTION Recently, the interest in electronic and photonic organic materials have greatly increased because of their utilization as active components in a number of electronic devises, such as organic light-emitting diodes (LED) and field effect transistors (FET) [1-4]. However, conjugated organic compounds have not been used in the commercial stage for electronic devises, because of the low physical stability. Then, we attempted to synthesis novel organic compounds, which exhibited satisfactorily thermal and photonic properties with a good processability. In this study, we have focused on indolo[3,2-b]carbazole (INC), which possessed the conjugated and planer structure and showed the blue fluorescence by the irradiation of UV light, and the syntheses of INC derivatives have been investigated. Some investigations of INC derivatives and polymers have already been reported for the use of FET [5]. However, only few studies have been reported on the synthesis for electronic and photonic properties of INC derivatives and polymers. The problems for the development of INC derivatives would be a poor solubility of the compound, INC, because of its strong intermolecular interaction derived from the planer structure. Therefore, it was difficult to introduce some substituents into INC by chemical reaction. The first purpose of our work is the synthesis of INC derivative which is soluble in ordinary organic solvents to develop the new compounds containing INC moiety with its unique photonic and electronic property. Hence, in order to improve the solubility of INC compound, N-alkylated INC derivatives were prepared by the reaction of INC with NaH followed by the addition of alkyl halides. On the other hand, the introduction of alkyl and polymerizable groups into Nposition of INC was carried out to produce a polymer containing INC moiety in the side chain, which had a filmformation property. Then, in this paper, the thermal and the photonic properties of the obtained N-alkylated INC and the polymer compounds will be discussed.
2.2 Photonic properties of INC and N-alkylated INC The ultraviolet-visible (UV-vis) adsorption and the photoluminescence spectra of INC and N-alkylated INC were measured in their dilute DMF solutions. The results
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Syntheses and Photonic Properties of Indolocarbazole Derivatives
142
CH 2
35 %-HCHO, CH3 COOH N H
H 2O
N H
reflux, overnight
H N
CH(OEt)3, conc. H 2SO4 MeOH
N H
N H
reflux, overnight
DIM
INC
R N INC
NaH DMF r.t., 0.5h
R-I 65℃, overnight N R
INC-Cm : R =
CH2
H m
N-alkylated INC
Scheme 1
Preparation of N-alkylated INC
are shown in Figures 1 and 2. As seen in Figure 1, it was found that UV adsorption spectra of N-alkylated INC were similar to that of INC. On the other hand, the photoluminescence spectra of N-alkylated INC showed a small red shift as compared to that of INC, which would be due to the increase of electron density of π-conjugated system by the substitution of alkyl groups at N-position. The photoluminescence quantum yield, Φx , was defined as the equation below;
Φx = Φst･(FAx/FAst)･(Ast/Ax)･(Iex,st/Iex,x)･(nx2/nst2)
(1)
where Φx and Φst are the photoluminescence quantum yield, FAx and FAst are the integrated area under the corrected emission spectra, Ast and Ax are the absorbance at the excited wavelength, Iex,st and Iex,x are the intensity of the excitation light, and nx and nst are the average refractive index of the solutions used for the luminescence of the unknown sample (x) and the reference sample (st), respectively. The photoluminescence spectra were measured in DMF, and the photoluminescence quantum yields were determined by using quinine sulfate (1N) as the reference sample [7]. The photoluminescence quantum yields of INC and INC derivatives are shown in Table 1. As seen in this table, the photoluminescence quantum yields of INC, INC-C1, INC-C5 and INC-C8 exhibited 0.50, 0.54, 0.52, and 0.53, respectively, where the values of N-alkylated INC were almost same as that of INC. Thus, it may be concluded that the photonic properties of INC moiety are not influenced by introducing alkyl chain into N-position of INC. 2.3 Polymers containing INC moiety In order to obtain the polymer containing INC moiety, INC derivatives containing a p-vinylbenzyl group, CMSINC-C1 and CMS-INC-C8, were prepared as monomer compounds. Then, polystyrene-type polymers with INC moiety were obtained by the radical polymerization of these monomers, as shown in Scheme 2. On the other hand, the polymer containing carbazole moiety, PCMS-Cz, was prepared as a reference, as shown in scheme 3. The weight-average molecular weights (Mw) of the obtained polymers, PCMS-INC-C1, PCMS-INC-C8, PCMS-Cz, were determined as absolute values by a Laserlight scattering method connected to GPC. Furthermore, thermal properties of these polymers were estimated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal properties of these polymers were summarized in Table 2. The glass transition temperature (Tg) of PCMS-INC-C1 was higher than that of PCMS-Cz. Therefore, it was revealed that INC moiety of the side structure was influenced on Tg of polymers, which would be due to the strong intermolecular interaction derived from the planer structure. In addition,
Figure 1 UV-vis spectra of INC and N-alkylated INC in the solution, the concentration of which was 1.0 x 10-6 M in DMF.
Figure 2 The photoluminescence spectra of INC and Nalkylated INC in the solution, the concentration of which was 1.0 x 10-6 M in DMF. Table 1 The calculated photoluminescence quantum yields of INC and N-alkylated INC.
a) Photoluminescence quantum yield, measured in DMF and determined by using quinine sulfate (1 N) as a standard.
Tg of PCMS-INC-C8 was lower than that of PCMS-INCC1 according to the mobility of octyl chain. On the other hand, as seen in Figure 3, UV-vis spectra patterns of the polymers containing INC moiety was similar to that of N-alkylated INC. Moreover, Figure 4 shows the photoluminescence patterns of PCMS-INC-C8 and PCMS-Cz, where the photoluminescence pattern of PCMS-INC-C8 was sifted to the longer wavelength as compared with that of PCMS-Cz. The maximum wavelength of photoluminescence of PCMS-INC-C8 was observed at 424 nm and 449 nm with a long extending to 530 nm, which was probably due to the excimer formation of INC moiety. This result would be regarded as a long extending of PCMS-Cz [8]. Moreover, the photoluminescence pattern of PCMS-INC-C8 film was also sifted to the longer wavelength and exhibited a broad
M. Akimoto et al.
34[1] 141-144 (2009)
Transaction of the Materials Research Society of Japan
R-I NaH
H N
(R= octhyl or methyl )
NaH
CH2 N
CH2 Cl
INC DMF r.t. 0.5 h
r.t.
DMF r.t. 0.5 h
N R
1h
r.t.
INC-MCm
CH
N R
overnight
CMS-INC-Cm
CH2
AIBN NMP 75℃ overnight
CMS-INC-Cm, PCMS-INC-Cm : R =
CH2 N
N R
CH 2
H m
PCMS-INC-C1: Mw = 40,000 PCMS-INC-C8: Mw = 58,900
n
PCMS-INC-Cm
Scheme 2
Preparations of INC-containing polymers. CH
H N
NaH
CH 2 Cl
DMF r.t. 0.5 h
r.t.
CH2 N
overnight
CH 2
AIBN CH2 N
NMP 75℃
n CMS-Cz
PCMS-Cz
PCMS-Cz: Mw = 23,300
Scheme 3
Preparation of carbazole-containing polymer.
Table 2 Thermal properties of polymers.
a) Tg was determined by DSC at a heating rate of 10℃/min. b) The temperatures at 5 % loss (Td5) and 10% loss (Td10) were estimated by TGA at heating rate of 10℃/min in N2.
Figure 3 UV-vis adsorption spectra of the polymers containing INC moiety in the solution, the concentration of which was 1.0 x 10-6 M in DMF.
peak as compared with that of PCMS-INC-C8 in DMF solution. 3. CONCLUSION The solubility of INC could be successfully improved by the alkylation of N-position of INC. Then, it was found that the photonic properties such as UV-vis adsorption and photoluminescence spectra of N-alkylated INC were similar to those of INC. On the other hand, the side-chain type polymer containing N-alkylated INC could be synthesized by a radical polymerization, Tg of which was higher than that of the similar polymer containing carbazole. Therefore, it was revealed that the INC moiety in the side
Figure 4 The photoluminescence spectra of PCMS-INC-C8 and PCMS-Cz, where the grey dash line: PCMS-Cz in DMF, the grey solid line: PCMS-Cz in film, the black dash line: PCMS-INC-C8 in DMF, black solid line: PCMS-INC-C8 in film. The emission wavelengths of PCMS-Cz solution, PCMSCz film, PCMS-INC-C8 solution, and PCMS-INC-C8 film were 294, 331, 395 and 342 nm, respectively. The concentration of polymer solution was 1.0 x 10-6 M in DMF, and the thickness of films was about 100 nm on quartz substrate.
chain was influenced on Tg of polymers. It was also found that the photonic properties of the polymer were similar to those of N-alkylated INC. Moreover, the result of photoluminescence of the polymer film suggested the strong aggregation of INC moiety in the side-chain. The synthesis of main-chain type INC polymer is now in progress to reveal the effect of INC moiety on the polymer property, for the development of new photonic and electronic materials. 4. EXPERIMENTAL 4.1 Materials INC was prepared by the procedure described in the literature [6]. Tetrahydrofuran (THF) was distilled over sodium to remove the small amount of water. Anhydrous
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Syntheses and Photonic Properties of Indolocarbazole Derivatives dimethylsulfoxide (DMSO), dimethylformamide (DMF) and 1-methyl-2-pyrrolidinone (NMP) were purchased from Aldrich Co., Ltd. 2,2’-Azobis(isobutyronitrile) (AIBN) was purified by recrystallization from ethanol. 4.2 5,11-Dioctyl-indolo[3,2-b]carbazole (INC-C8) Under an argon atmosphere, sodium hydride (60 % NaH in oil, 0.787 g, 19.7 mmol) was dispersed in 21 mL of DMSO, and the mixture was stirred at 60 ℃for 1 h. To this solution, INC (2.00 g, 7.87 mmol) was added and the mixture was stirred at 60 ℃ for 3 h. After 1-iodooctane (4.26 mL, 23.6 mmol) was added to this solution, it was stirred at 60 ℃ for 22 h. Then, the reaction mixture was poured into 1 L of methanol to obtain the crude product. The product was purified by column chromatography on silica gel with hexane and recrystallization with ethanol and chloroform to afford 0.89 g of INC-C8. Yield: 23.6 %. 1 H-NMR δ (400 MHz, DMSO, ppm): 0.78 (6H, t, J = 6.6 Hz), 1.25 (m, 23 H), 1.84 (m, 4H), 4.46 (t, 4H, J = 6.8 Hz), 7.17 (t, 2H, J = 7.6 Hz), 7.44 (t, 2H, J = 7.2 H), 7.55 (d, 2H, J = 8.0), 8.26 (d, 2H, J = 7.6 Hz), 8.30 (s, 2H). Other N-alkylated INCs were prepared by the same procedure as above using other iodoalkanes (C1 – C10) instead of 1-iodooctane. 4.3 9-(4-Vinylbenzyl)carbazole (CMS-Cz) Under an argon atmosphere, sodium hydride (60 % NaH in oil, 7.16 g, 180 mmol) was dispersed in 260 mL of THF, and the mixture was stirred at 0℃ for 30 min. To this solution, carbazole (20.0 g, 120 mmol) was added and the mixture was stirred at 0 ℃ for 30 min. After pchloromethylstyrene (21.9 g , 144 mmol) was added to this solution, it was stirred at 50℃ for 24 h. Then, the reaction mixture was poured into 2 L of methanol to obtain the crude product. The product was purified by recrystallization with ethanol and chloroform to afford 18.0 g of CMS-Cz. Yield: 53.0 %. 1 H-NMR δ (400MHz, DMSO, ppm): 5.20 (d, 1H, J = 10.8 Hz), 5.64 (2H, s), 5.73 (1H, d, J =17.6 Hz), 6.63 (q, H), 7.13 (2H, d, J = 8.4 Hz), 7.20 (2H, t, J = 7.6 Hz), 7.34 (2H, d, J = 7.6 Hz), 7.42 (2H, t, J = 7.2 Hz), 7.61 (2H, d, 8.4 Hz), 8.17 (2H, d, J = 7.6 Hz). 4.4 5-Octyl-11-hydroindolo[3,2-b]carbazole (INC-MC8) Under an argon atmosphere, sodium hydride (60% NaH in oil, 3.43g, 85.8 mmol) was dispersed in 200 mL of DMF, and the mixture was stirred at r.t. for 30 min. To this solution, INC (10.0 g, 39.0 mmol) was added and the mixture was stirred at r.t. for 1 h. After 1-chlorooctane (5.80 g, 39.0 mmol) was added to this solution, the mixture was stirred at 0 ℃ for 3 h. Then, the reaction mixture was poured into excess amount of water, and the obtained product was extracted with chloroform. Finally, the product was purified by recrystallization with ethyl acetate and ethanol to afford 2.50 g of INC-MC8. Yield: 17.0 %. 1 H-NMR δ (400MHz, DMSO, ppm): 0.78 (3H, t, J = 6.84 Hz), 1.19 (6H, m), 1.31 (4H, m), 1.83 (2H, m), 4.42 (2H, t, J = 6.84 Hz), 7.14 (2H, m), 7.36 (1H, t, J = 7.39 Hz), 7.45 (1H, d, J = 7.88 Hz), 7.53 (1H, d, J = 8.33 Hz), 8.21 (2H, m), 8.24 (1H, s), 11.1 (1H, s). INC-MC1 was prepared by the same procedure as above using iodomethane instead of 1-chlorooctane. 4.5 5-Octyl-11-(4-vinylbenzyl)indolo[3,2-b]carbazole (CMS-INC-C8)
Under an argon atmosphere, sodium hydride (60 % NaH in oil, 0.816 g, 20.4 mmol) was dispersed in 68 mL of DMF, and the mixture was stirred at 0℃ for 30 min. To this solution, INC-MC8 (5.00 g, 13.6 mmol) was added and the mixture was stirred at 0℃ for 30 min. After pchloromethylstyrene (3.11 g , 20.4 mmol) was added to this solution, it was stirred at 70℃ for 24 h. Then, the reaction mixture was poured into 2 L of methanol to obtain the crude product. The product was purified by recrystallization with ethanol and chloroform to afford 4.88 g of CMS-INC-C8. Yield: 74.1 %. 1 H-NMR δ (400 MHz, DMSO, ppm): 0.79 (3H, t, J = 6.6 Hz), 1.25 (10H, m), 1.84 (2H, m), 4.46 (2H, t, J = 6.8 Hz), 5.16 (1H, d, J = 11.2 Hz), 5.69 (1H, d), 5.73 (2H, s), 6.63 (1H, q), 7.17 (4H, m), 7.35 (2H, d, J = 8.4 Hz), 7.43 (2H, m), 7.56 (2H, m), 8.19 (1H, d, J = 7.6 Hz), 8.29 (1H, d, J = 7.6 Hz), 8.35 (1H, s), 8.35 (1H, s). CMS-INC-MC1 was prepared by the same procedure as above using INC-MC1 instead of INC-MC8. 4.6 Polymerizations Under an argon atmosphere, CMS-INC-C1 (1.0 g, 2.59 mmol), CMS-INC-C8 (1.0 g, 2.01 mmol) or CMS-Cz (1.5 g, 5.29 mmol) was dissolved with AIBN (0.0851 g, 0.518 mmol) in 10 mL of NMP. Then, the mixtures were stirred at 75℃ for overnight. Finally, the reaction mixtures were poured into an excess amount of methanol to precipitate the polymers, to afford 0.60 g of PCMS-INC-C1 (Yield: 60.1 %), 0.50 g of CMS-INC-C8 (Yield: 50.0 %) and 0.60 g of PCMS-Cz (Yield: 30.0 %), respectively. Mw = 40,000 (PCMS-INC-C1), 58,900 (CMS-INC-C8), 23,300 (PCMS-Cz). 4.7 Characterizations 1 H-NMR spectroscopy was conducted with a JEOL NM-TH5SK 400MHz FT-NMR. The molecular weights of polymers were estimated by a Tohso HCL-802A instrument by using THF as eluent, equipped with four columns of TSK gels G5000H6, G4000H6, G3000H6 and G2000H6. The elution was detected by RI and Laser light scatting detectors using Tohso LS-8000 to obtain weightaverage molecular weight (Mw). DSC and TGA were carried out on a Seiko Instruments DSC-6200 and TG/DTA-6200, respectively, at a heating rate of 10℃/min under a nitrogen atmosphere. UV-vis adsorption and photoluminescence spectra were measured by JEOL V-530 and SHIMADZU RF-5300PC, respectively. 5. REFERENCES [1] R. Gu, A. Hameurlaine, W. Dehaen, J. Org. Chem. 72 (2007) 7207-7213. [2] I. Levesque, P. Bertrand, N. Blouin, M. Leclerc, S. Zecchin, G. Zotti, C. Ratcliffe, D. Klug, X. Gao, F. Gao, J. Tse, Chem. Matter. 19 (2007) 2128-2138. [3] Y. Li, Y. Wu, S. Sandra, B. Ong, Adv. Mater. 17 (2005) 849-852. [4] Y. Wu, Y. Li, S. Gardner, B. Ong, J. Am. Chem. Soc. 127 (2005) 614-618. [5] Y. Li, Y. Wu, B. Ong, Macromolecules 39 (2006) 6521-6527. [6] U. Pindur, Arch. Pharm. (Weinheim) 320 (1987) 282284. [7] J. N. Demas, G. A. Crosby, J. Phys. Chem. 75 (1971) 991-1024. [8] Y. Cho, S. Kim, C. Ihn, J. Lee, Polymer 42 (2001) 7611-7616. (Received December 12, 2008; Accepted January 28, 2009)
