Synthesis and luminescent properties of novel condensed copolymers

Synthesis and luminescent properties of novel condensed copolymers

Synthetic Metals 111–112 Ž2000. 477–479 www.elsevier.comrlocatersynmet Synthesis and luminescent properties of novel condensed copolymers Weihong Zhu...

98KB Sizes 1 Downloads 146 Views

Synthetic Metals 111–112 Ž2000. 477–479 www.elsevier.comrlocatersynmet

Synthesis and luminescent properties of novel condensed copolymers Weihong Zhu, Yongbo Hu, He Tian ) Institute of Fine Chemicals, East China UniÕersity of Science and Technology, Shanghai 200237, People’s Republic of China

Abstract Three novel polymeric materials containing isolated naphthalimide and oxadiazole moieties as part of the polymer main chain were prepared by polycondensation. The contents of chromophore moieties were characterized using various spectroscopic techniques, such as the standline method of UV–Vis spectra and 1 H-NMR. The luminescent properties of these polymers have been also studied. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Condensed polymers; Naphthalimide; Oxadiazole moiety; Luminescent property

1. Introduction Much attention has been devoted to develop new polymeric materials for application in electroluminescent ŽEL. devices. Considering that the dispersion of small organic molecules in a polymer would less likely exhibit long-term morphological stability, new oxadiazole polymers for EL devices have been reported to enhance the electron-transporting capability, which have high thermal stability and excellent film forming properties w1x. A variety of polyester containing oxadiazole moiety at the side chain for EL device had also been synthesized w2x. Here, we report a novel condensed polymer containing emitter moiety Žnaphthalimide, NA. and electron-transporting moiety Žoxadiazole, OXZ. within the polymer main chain Žshown in Fig. 1.. Such assembling polymers based on isolated chromophores within the main chain would have high electron injection efficiency than that of chromophores at the side chain.

2. Experimental A typical polymerization ŽPŽNA1-OXZ.. was carried out as follows: NA Ž0.30 g, 1.0 mmol., OXZ Ž0.25 g, 1.0

)

Corresponding author. E-mail address: [email protected] ŽH. Tian..

mmol., 1,4-butandiol Ž0.36 g, 4.0 mmol. and 10 ml N, Ndimethylacetamide were placed into a dry flask. The solution was stirred and cooled to 08 and 1,10-decanedioyl chloride Ž1.44 g, 6.0 mmol. was then added all at once. The solution was stirred for an hour and then the temperature was permitted to rise to 258C. After 8 h, the polymerization was assumed to be complete and the resulting solution was poured into 150 ml water and the precipitate was filtered and washed with water and tetrahydrofuran to give greenish yellow solid PŽNA1–OXZ. 1.5 g. The average molecular weight determined by using gel permeation chromatography ŽGPC. method based on polystyrene standards was about 12 000. PŽNA2–OXZ., PŽNA3–OXZ. were synthesized in a similar way. UV–Vis spectra were recorded on a Shimdatzu UV-260 spectrometer and fluorescence spectra were determined with a Hitachi-850 fluorescence spectrometer. 1 H-NMR spectra were recorded on a Brucker AM500 spectrometer with tetramethylsilane as internal reference. The average molecular weight of copolymer was obtained with a Waters 410 GPC. The monomers of N,4-bis Ž2-hydroxyethyl.-1, 8-naphthalimide and 2,5-bis Ž4-aminophenyl.-1,3,5-oxadiazole were synthesized as described in the literature w3,4x, respectively. NA: m.p.: 222–2248C. 1 H-NMR Žin d 6-DMSO.: 3.36 Žs, 2H., 3.47 Žt, 2H, J s 5.3 Hz, 5.4 Hz., 3.57 Žt, 2H, J s 6.6 Hz, 6.5 Hz., 3.70 Žt, 2H, J s 5.9 Hz, 5.6 Hz., 4.12 Žt, 2H, J s 6.6 Hz, 6.5 Hz., 6.81 Žd, 1H, J s 8.6 Hz., 7.68 Žm, 1H., 8.25 Žd, 1H, J s 8.5 Hz., 8.42 Žd, 1H, J s 7.2 Hz., 8.68 Žd, 1H, J s 8.4 Hz.. OXZ: m.p.: 260–2628C. 1 H-

0379-6779r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 Ž 9 9 . 0 0 4 2 2 - 1

W. Zhu et al.r Synthetic Metals 111–112 (2000) 477–479 478

Fig. 1. The schematic chemical structures of polymers.

Fig. 2. UV–Vis absorption standline of 2,5-bisŽ4-acetylamino phenyl.1,3,5-oxadiazole Žsolid line . and N,4-bisŽ2-hydroxyethyl. -1,8naphthalimide Ždot line..

NMR Žin d 6-DMSO.: 5.88 Žs, 4H., 6.70 Žd, 4H, J s 8.3 Hz., 7.71 Žd, 4H, J s 8.3 Hz..

3. Results and discussion The content of naphthalimide and oxadiazole moieties in the condensed polymers is determined using the standline method of UV-spectra Žshown in Fig. 2., which is based on the hypothesis that the absorption of NA and OXZ moieties are the same absorption as N,4-bisŽ2-hydroxyethyl.-1,8-naphthalimide and 2,5-bis Ž4-acetylaminophenyl.-1,3,5-oxadiazole, respectively. Hence, we can determine the content of NA and OXZ moieties Žlisted in Table 1.. We also apply the 1 H-NMR to determine that the mole ratio of NA and OXZ in PŽNA1–OXZ. is 1.78, which is

similar to the ratio obtained by standline method of UVspectra Ž1.62. and demonstrates that our above hypothesis is reasonable. Using the same analytic method, we also obtain the mole ratio of NA and OXZ in PŽNA2–OXZ. and PŽNA3–OXZ. are 0.86 and 1.07, respectively. Fig. 3 illustrates the UV–Vis absorption and PL spectra of PŽNA1–OXZ. in DMF. Comparing with absorption spectra of the corresponding mixture of 1,8-naphthalimide and oxadiazole, the absorption of the polymer in DMF is the exact sum of that of the constituent chromophores. This indicates that there is little or no interaction between chromophores in their ground state, so that their individual characteristics should be maintained. As to PL spectra, two peaks Ž377 and 524 nm. can be observed, which are the emission of OXZ and NA moieties, respectively. Due to the larger overlap between the absorption of NA moiety and emission of OXZ moiety in the condensed polymers, there exists an effective intramolecular singlet–singlet energy transfer, so, the emission of OXZ is quenched and the peak of OXZ emission Ž377 nm. is very low. It is consistent with our previous organic small dyad molecules w5,6x. With respect to the complication and instability of doping, these polymers could be hopeful to be utilized in EL devices. We also observe the phenomenon in the PL spectrum of thin solid film on ITO. However, owing to the

Table 1 The content of NA and OXZ moieties in the condensed polymers Žwrw%.

PŽNA1–OXZ. PŽNA2–OXZ. PŽNA3–OXZ.

NA moiety Ž%.

OXZ moiety Ž%.

13.2 16.8 19.6

6.9 16.2 15.2

Fig. 3. UV–Vis absorption spectrum Žcurve a. and PL spectra of PŽNA1– OXZ. in DMF Žcurve b. and thin solid film on ITO Žcurve c. Žexcited at 320 and 441.6 nm, respectively..

W. Zhu et al.r Synthetic Metals 111–112 (2000) 477–479 479

solid aggregative effect, the PL peak of thin solid film shifts bathochromically from 524 nm to 540 nm compared with PL spectrum in DMF solution Žshown in Fig. 3.. The copolymers of PŽNA2–OXZ. and PŽNA3–OXZ. also show the similar PL properties.

Acknowledgements This work was supported by NFSC ŽProject No. 29625611..

References w1x E. Buchwald, M. Meier, S. Karg, P. Poesch, P. Strohriegel, W. Riess, M. Schwoerer, Adv. Mater. 7 Ž1995. 839. w2x X.C. Li, F. Cacialli, M. Giles, R.H. Friend, A.B. Holmes, S.C. Moratti, T.M. Yong, Adv. Mater. 7 Ž1995. 898. w3x T. Philipova, Rev. Roum. Chim. 41 Ž1996. 591. w4x J. Preton, J. Heterocycl. Chem. 2 Ž1965. 441. w5x W.H. Zhu, C. Hu, H. Tian, Synth. Met. 96 Ž1998. 151. w6x H. Tian, W.J. Ni, J.H. Su, K.C. Chen, J. Photochem. Photobiol. A: Chem. 109 Ž1997. 213.