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Various chemical modifications of oligothienyls and oligophenyls
ELSEVIER
Synthetic Metals 101 (1999) 551-552
Various chemical modifications of oligothienyls and oligophenyls S. Hotta’s*, S. A. Leeb ‘Joint Research Center for Harmonized Molecular Materials (JRCHMM)-Japan Chemical Innovation Institute, c/o National Institute of Materials and Chemical Research, l-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan “iMolecular Function Group, Department of Molecular Engineering, National Institute of Materials and Chemical Research, l-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Abstract Chemical modifications of oligothienyls and oligophenyls were carried out by organosynthetic routes. As one of these attempts, we have exploited a series of cooligomers based on thienyls and phenyls. Extension of the n-conjugation can be altered by changing the total number of the thienyls and phenyls and their mutual arrangement. This leads to a variety of interesting aspects. Keyword: Cooligomers; Oligothienyls; Oligophenyls; Electronic and photonic devices; Molecular layered structure; Fluorescence
1. Introduction
3. Results and Discussion
Oligothienyls and oligophenyls are counted among major organic semiconductors. Researchers are currently making a number of attempts to apply these materials to electronic and photonic devices [1,2]. To supply these two classes of materials with broader versatility, their hybridization is highly desired. To this end we have carried out various chemical modifications of the oligothienyls and oligophenyls. Within this framework, in particular, we have exploited a series of cooligomers based upon thienyls and phenyls. Ahhough a few such compounds with low molecular weight [3] were synthesized, neither systematic syntheses nor investigations have yet been carried out from the point of view of extensively studying physicochemical properties of the materials. In this article we present initial results relevant to the syntheses and characterization of the above-mentioned cooligomers, a new class of organic semiconductors in which the oligothienyls and oligophenyls are hybridized at molecular level.
Figure 1 shows several chemical structures of the cooligomers. As noted immediately, a variety of compounds are readily accessible by changing the total number of the thienyls and phenyls and their mutual arrangement in the molecule. The molecular structure can be determined from the IR spectra. When the compound has QI, a ‘-disubstituted thiophenes, sharp peaks due to the ring stretching and the CH out-of-plane modes occur around 1440 and 790 cm.‘, respectively [1.6]. For the molecules with Q:-monosubstituted thiophenes at the terminal positions those modes arise at 1420 and 700 cm“ [6]. The presence (or absence) of mono and 1,4-disubstituted benzenes was examined analogously. Figure 2 displays typical results of the 8 -2 8 diffraction measurements. The primary spacings of 13.2 and 16.4 A are observed for the compounds 1 and 2, respectively. Higher-order reflections are clearly resolved up to the tenth order. Virtually the same trend can be seen for other cooligomers. These features are closely related to those confirmed for a series of oligothienyls with various polymerization degrees [l] and demonstrate the presence of the molecular layered structure.
2. Experimenta We synthesized the cooligomers with combination of Grignard coupling [4] and Suzuki coupling [S]. The compounds were purified through their recrystallization from a suitable solvent. Thin films were prepared either by casting solutions or by directly evaporating the materials. IR transmission measurements were carried out using KE%r pressed disks in which the finely ground material was embedded. Transmission and emission spectra of the cooligomers were recorded with their solutions and thin films. The 8 -2 8 X-ray diffraction measurements were carried out with the thin films. “Corresponding author. Tel. and fax: t81 298 60 6242; e-mail: [email protected]
Fig. 1. Chemical Structures of several cooligomers. Note that the structures do not necessarily represent the real conformation.
0379~6779/99/$- see front matter 0 1999 Elsevier ScienceS.A. All rights reserved, PII: SO379-6779(98)00845-5
552
S. Hotta, S.A. Lee I Synthetic Met&
Most striking features of the cooligomers show themselves in optical properties. This is because extension of the ?Gconjugation can be readily altered as desired, producing various colors (resulting either from transmission or emission). As an example, Fig. 3 shows fluorescence emission spectra for a 1w6M cooligomer solution in dichloromethane or chloroform. Several aspects can be derived: Generally, the spectra are redshifted with increasing ring number, which is usually the case with other n-conjugated materials as well [7]. As a result, the spectral range spans ca. 380 to 530 nm (as peak positions) for the 3- to 6-ring systems. Here the ring number represents the total number of the thienyls and phenyls. Within the same ring-number systems, however, pretty large shifts in the peak positions are noticed according to the change in the arrangement of thienyls and phenyls (see Fig. 3). The longer cooligomers exhibit two major peaks that are associated with the vibronic coupling [1,7]. This probably reflects the presence of the stiff quinoid structure involved in the excited state. Similarity between the fluorescence excitation spectra and the UV-vis absorption ones for the individual compounds implies that the fluorescence comesfrom excited monomer species.
101 (1999) SSl-552
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4. Conclusion We have carried out various chemical modifications of the oligothienyls and oligophenyls. In particular, we have exploited a series of cooligomers based upon thienyls and phenyls. The morphology of their thin films is characterized by the molecular layered structure. Depending on the extension of the it conjugation, these cooligomers show various interesting features. For example, the spectra cover a wide range of wavelengths. These features will enable us to make the most of the cooligomers in the present studies on the advanced electronic and photonic devices.
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28 Angle (degrees) Fig. 2. The X-ray 0 -2 8 profiles for the solution-cast films of (a) PTP (1) and (b) PTTP (2), where T and P denote a thienyl and phenyl, respectively.
Acknowledgements We thank Dr. Y. Yoshida, Dr. F. Nakanishi, and Dr. T. Tamaki, National Institute of Materials and Chemical Research (NIMC), for their helpful discussions and suggestions. Thanks are also due to Dr. H. Fukushima, JRCHMM, for his valuable suggestions on the organosynthetic techniques. This work was supported by NED0 for the Harmonized Molecular Materials theme funded through the project on Technology for Novel High-Functional Materials (AIST).
References [l] S. Hotta, in H. S. Nalwa (ed.), Handbook of Organic Conductive Molecules and Polymers, John Wiley & Sons, Chichester, 1997, Vol. 2, Chap. 8. [2] D. Fichou, S. Delysse, J.-M. Nunzi, Adv. Mater. 9 (1997) 1178. [3] T. Mitsuhara, K. Kaeriyama, S. Tanaka, J. Chem. Sot., Chem. Commun. (1987) 764. [4] K. Tamao, S. Kodama, I. Nakajima, M. Kumada, A. Minato, K. Suzuki, Tetrahedron 38 (1982) 3347, [5] N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457. [6] R. F. Curtis, G. T. Phillips, Tetrahedron 23 (1967) 4419: [7] R. S. Becker, J. S. de Melo, A. L. Macanita, F. Elisei, J. Phys. Chem. 100 (1996) 18683.
I
400
450
550
500
Wavelength
600
(nm)
Fig. 3. Emission spectra of various cooligomers in solution. The curves a, b, c, d, e, f, and g stand for TPT, PTP, TPPT, TTPP, PTTP, PITTP, and PTTTTP, respectively. We used as a solvent dichloromethane for the former four species and chloroform for the latter three.
Synthetic Metals 101 (1999) 551-552
Various chemical modifications of oligothienyls and oligophenyls S. Hotta’s*, S. A. Leeb ‘Joint Research Center for Harmonized Molecular Materials (JRCHMM)-Japan Chemical Innovation Institute, c/o National Institute of Materials and Chemical Research, l-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan “iMolecular Function Group, Department of Molecular Engineering, National Institute of Materials and Chemical Research, l-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Abstract Chemical modifications of oligothienyls and oligophenyls were carried out by organosynthetic routes. As one of these attempts, we have exploited a series of cooligomers based on thienyls and phenyls. Extension of the n-conjugation can be altered by changing the total number of the thienyls and phenyls and their mutual arrangement. This leads to a variety of interesting aspects. Keyword: Cooligomers; Oligothienyls; Oligophenyls; Electronic and photonic devices; Molecular layered structure; Fluorescence
1. Introduction
3. Results and Discussion
Oligothienyls and oligophenyls are counted among major organic semiconductors. Researchers are currently making a number of attempts to apply these materials to electronic and photonic devices [1,2]. To supply these two classes of materials with broader versatility, their hybridization is highly desired. To this end we have carried out various chemical modifications of the oligothienyls and oligophenyls. Within this framework, in particular, we have exploited a series of cooligomers based upon thienyls and phenyls. Ahhough a few such compounds with low molecular weight [3] were synthesized, neither systematic syntheses nor investigations have yet been carried out from the point of view of extensively studying physicochemical properties of the materials. In this article we present initial results relevant to the syntheses and characterization of the above-mentioned cooligomers, a new class of organic semiconductors in which the oligothienyls and oligophenyls are hybridized at molecular level.
Figure 1 shows several chemical structures of the cooligomers. As noted immediately, a variety of compounds are readily accessible by changing the total number of the thienyls and phenyls and their mutual arrangement in the molecule. The molecular structure can be determined from the IR spectra. When the compound has QI, a ‘-disubstituted thiophenes, sharp peaks due to the ring stretching and the CH out-of-plane modes occur around 1440 and 790 cm.‘, respectively [1.6]. For the molecules with Q:-monosubstituted thiophenes at the terminal positions those modes arise at 1420 and 700 cm“ [6]. The presence (or absence) of mono and 1,4-disubstituted benzenes was examined analogously. Figure 2 displays typical results of the 8 -2 8 diffraction measurements. The primary spacings of 13.2 and 16.4 A are observed for the compounds 1 and 2, respectively. Higher-order reflections are clearly resolved up to the tenth order. Virtually the same trend can be seen for other cooligomers. These features are closely related to those confirmed for a series of oligothienyls with various polymerization degrees [l] and demonstrate the presence of the molecular layered structure.
2. Experimenta We synthesized the cooligomers with combination of Grignard coupling [4] and Suzuki coupling [S]. The compounds were purified through their recrystallization from a suitable solvent. Thin films were prepared either by casting solutions or by directly evaporating the materials. IR transmission measurements were carried out using KE%r pressed disks in which the finely ground material was embedded. Transmission and emission spectra of the cooligomers were recorded with their solutions and thin films. The 8 -2 8 X-ray diffraction measurements were carried out with the thin films. “Corresponding author. Tel. and fax: t81 298 60 6242; e-mail: [email protected]
Fig. 1. Chemical Structures of several cooligomers. Note that the structures do not necessarily represent the real conformation.
0379~6779/99/$- see front matter 0 1999 Elsevier ScienceS.A. All rights reserved, PII: SO379-6779(98)00845-5
552
S. Hotta, S.A. Lee I Synthetic Met&
Most striking features of the cooligomers show themselves in optical properties. This is because extension of the ?Gconjugation can be readily altered as desired, producing various colors (resulting either from transmission or emission). As an example, Fig. 3 shows fluorescence emission spectra for a 1w6M cooligomer solution in dichloromethane or chloroform. Several aspects can be derived: Generally, the spectra are redshifted with increasing ring number, which is usually the case with other n-conjugated materials as well [7]. As a result, the spectral range spans ca. 380 to 530 nm (as peak positions) for the 3- to 6-ring systems. Here the ring number represents the total number of the thienyls and phenyls. Within the same ring-number systems, however, pretty large shifts in the peak positions are noticed according to the change in the arrangement of thienyls and phenyls (see Fig. 3). The longer cooligomers exhibit two major peaks that are associated with the vibronic coupling [1,7]. This probably reflects the presence of the stiff quinoid structure involved in the excited state. Similarity between the fluorescence excitation spectra and the UV-vis absorption ones for the individual compounds implies that the fluorescence comesfrom excited monomer species.
101 (1999) SSl-552
G-4
5
3.0
10.0
40.0
30-O
20.0 -
50.0
60.0
28 Angle (degrees)
1
4. Conclusion We have carried out various chemical modifications of the oligothienyls and oligophenyls. In particular, we have exploited a series of cooligomers based upon thienyls and phenyls. The morphology of their thin films is characterized by the molecular layered structure. Depending on the extension of the it conjugation, these cooligomers show various interesting features. For example, the spectra cover a wide range of wavelengths. These features will enable us to make the most of the cooligomers in the present studies on the advanced electronic and photonic devices.
3.0
10.0
20.0
30.0
40.0
50.0
61
28 Angle (degrees) Fig. 2. The X-ray 0 -2 8 profiles for the solution-cast films of (a) PTP (1) and (b) PTTP (2), where T and P denote a thienyl and phenyl, respectively.
Acknowledgements We thank Dr. Y. Yoshida, Dr. F. Nakanishi, and Dr. T. Tamaki, National Institute of Materials and Chemical Research (NIMC), for their helpful discussions and suggestions. Thanks are also due to Dr. H. Fukushima, JRCHMM, for his valuable suggestions on the organosynthetic techniques. This work was supported by NED0 for the Harmonized Molecular Materials theme funded through the project on Technology for Novel High-Functional Materials (AIST).
References [l] S. Hotta, in H. S. Nalwa (ed.), Handbook of Organic Conductive Molecules and Polymers, John Wiley & Sons, Chichester, 1997, Vol. 2, Chap. 8. [2] D. Fichou, S. Delysse, J.-M. Nunzi, Adv. Mater. 9 (1997) 1178. [3] T. Mitsuhara, K. Kaeriyama, S. Tanaka, J. Chem. Sot., Chem. Commun. (1987) 764. [4] K. Tamao, S. Kodama, I. Nakajima, M. Kumada, A. Minato, K. Suzuki, Tetrahedron 38 (1982) 3347, [5] N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457. [6] R. F. Curtis, G. T. Phillips, Tetrahedron 23 (1967) 4419: [7] R. S. Becker, J. S. de Melo, A. L. Macanita, F. Elisei, J. Phys. Chem. 100 (1996) 18683.
I
400
450
550
500
Wavelength
600
(nm)
Fig. 3. Emission spectra of various cooligomers in solution. The curves a, b, c, d, e, f, and g stand for TPT, PTP, TPPT, TTPP, PTTP, PITTP, and PTTTTP, respectively. We used as a solvent dichloromethane for the former four species and chloroform for the latter three.