Abstract
In this paper, the synthesis of terpolymers bearing carbazole, coumarin and 8-hydroxyquinoline moiety as pendant groups with content of coumarin and 8-hydroxyquinoline between 0.5 and 4 mol% was elaborated. Then the terpolymers underwent complexation reactions with aluminum bis(8-hydroxyquinoline)isopropoxylate (Alq2ispr) to form polymeric hybrid materials with aluminum tris(8-hydroxyquinoline) (Alq3) as side groups. The presence of carbazole, coumarin (MK) and 8-hydroxyquinoline (QM) as well as Alq3 in the terpolymers was confirmed by NMR, UV, photoluminescence, and size exclusion chromatography. The results indicates that these hybrid polymers have moderate molecular weights and solubility in common organic solvents. For photoluminescence spectra, an evidence for energy transfer from carbazole to coumarin and Alq3 groups was observed and highest relative fluorescence intensity was exhibited by solutions of the terpolymers containing the lowest content of MK, QM and Alq3.
Introduction
Aluminum tris(8-hydroxyquinoline) (Alq3) is a common element in the construction of optoelectronic multilayer devices [1], [2]. It owes its application to very stable and efficient luminescence in the solid state, which is the effect of increased electron conductivity [3], [4]. The methods of producing thin Alq3 layers under vacuum conditions are not suitable for larger scale applications because of the possibility of thermal degradation of chelates and difficulty in obtaining repeatability of luminescent properties. An alternative, fast and less expensive technique for producing elements of optoelectronic devices in academic and industrial laboratories are spincoating, deepcoating, ink-jet printing, printing from a coil to a coil [5], [6]. The incorporation Alq3 material into a polymer is one of solution for employing low-cost solution-processing techniques. Moreover, Alq3-functionalized polymers also should be suitable for the fabrication of flexible displays with long-term mechanical stability. Hybrid polymers with Alq3 can be obtained in the form of: polymer blends and covalently incorporated into the structure of polymers of coordination compounds. The first method consists in the physical dispersion of the chelate in a selected polymer matrix: polystyrene (PS) [7], polymethacrylate (PMMA) [8], poly (N-vinylcarbazole) PVK [9], [10], poly(2,5)-dioctyloxy-p-phenylenevinylene (ROPPV-8) [11], poly (3,4-ethylene-1,4-dioxythiophene) (PEDOT) [12]; however, it often suffers from the low solubility of Alq3 in a polymer matrix and phase separation or formation of local ordered domains due to dipole–dipole interaction which can lead to poor optical properties in these systems [13], [14].
For the first time, Hay et al. successfully prepared Alq3-containing polymer by the attachment of 8-hydroxyquinoline moieties to poly(arylene ether) as a side chain and a subsequent reaction with triethylaluminum to form Alq3 complexes [15]. As the result, very rigid (Tg=203 °C) and resistant (Td>500 °C) hybrid polymers were obtained that formed a transparent and tough film up to 20 wt% concentration of Alq3 in the material.
Then Meyers and Weck synthesized functional coordination complex of Alq3 containing norbornene ligand allowing polymerization by ROMP mechanism [16]. Performing copolymerization with other non-functionalized alkyl derivatives of norbornene in the presence of Grubbs catalyst, they obtained non-crosslinked CHCl3 soluble copolymers (PDI=1.53–1.74,
Later, Kudo et al. presented the concept of synthesis of soluble polyacrylates containing Alq3 [18]. Polymethacrylate having a pendent Alq3 moiety was prepared using Kelex-100 (7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline) as a starting material. Solutions and films made of hybrid homopolymers showed similar optical properties to Alq3 i.e. λAbs=406–410 nm and λEx=537 nm. Another method to obtained soluble polyacrylates with Alq3 pendant group was introduced by Lu et al. by copolymerization with MMA monofunctional Alq3.The copolymers with 25 wt% Alq3 were still dissolved in common solvents without crosslinking, while photoluminescence efficiency reached ca. 20 % [19].
Eventually, improve the hole-transporting properties of Alq3, carbazole was attached to 8-hydroquinoline to obtain a polymerizable bipolar quinoline aluminum monomer. Moreover, N-vinylcarbazole was also chosen as a component to construct the copolymer backbone. The copolymers exhibited excellent thermal stability (Td>363 °C) and higher glass transition temperature (Tg>211°) than the common used light-emitting conjugated polymers. In particular, due to the energy transfer from carbazole units to the Alq3 moieties, the bipolar copolymers have good PL properties [20].
Because carbazole and its derivatives are one of the main interests in our laboratory [21], [22], [23], in the present paper, we report for the first time the synthesis of terpolymers containing Alq3 moiety together with carbazole and coumarin as the pendant groups and spectral characterization of these copolymers in comparison the spectral characterization of the monomers.
Experimental
Characterization
FT-IR spectra in the range of 4000–650 cm−1 were recorded on a Perkin Elmer Spectrum ATR apparatus.
1H, 13C NMR spectra were recorded on a Tesla 487C (80 MHz) and a Varian® Mercury-VX 300 MHz instruments with TMS as the internal standard.
Gas Chromatography (GC-FID) – Agilent® 6850 instrumentation column HP-1 30 m, 0.25 mm×0.25 μm, FID detector, qualitative analysis, preliminary determination of the purity of the compounds obtained.
Liquid chromatography with a mass spectrometer (LC-ESI-MS) – The analyzes were carried out on an ultrahigh performance liquid chromatographic Aquity UPLC from Waters® with a UV-VIS detector coupled with a ACQUITY TQD tandem mass spectrometer. The separation was carried out in gradient elution mode (MeCN: H2O) in the reversed phase system.
Size Exclusion Chromatography (SEC) – molecular weight and molecular weight distributions of polymers were determined on a Knauer® instrument using a five-column PL-gel system (250×8 mm), particle size 10 μm, refractometer or UV-VIS detector. Calibration of the columns was based on Watters® polystyrene standards. The data processing was based on a specific polynomial standard equation using the Chroma program.
Preparation of polymers
Monomer synthesis
9-(2-Hydroxyethyl)carbazole
In a flask equipped with a stirrer, 500 mL of dehydrated DMF were placed and carbazole (90 g, 0.54 mol) was dissolved therein. Subsequently, fresh well powdered KOH (60 g) was added in portions to the mixture during 1 h. Then 2-chloroethanol (40 mL, 0.57 mol) was added dropwise to the mixture at room temperature for 3 h. After 72 h, the mixture was poured into 5 L of water, and the resulting white precipitate was filtered, rinsed with water and dried. In the next step, the precipitate was dissolved in 300 mL of 70 % methanol with stirring for 2 h, and insoluble impurities were filtered off. Water was added to the filtrate to completely precipitate the compound, which was then filtered, washed with water and dried. Further purification of the product was carried out by recrystallization twice from ethanol. Yield: 80 %, m.p. 76–78 °C [24].
ESI-MS m/z=212.21 [M-H]+.
FTIR (KBr, [cm−1]): ν=3419 (w), 3213 (w), 3048 (w), 2976 (w), 2955 (w), 2937 (w), 2918 (w), 2868 (w), 1687 (m), 1656 (m), 1595 (m), 1485 (s), 1458 (s), 1388 (m), 1364 (s), 1350 (s), 1326 (s), 1245 (m), 751 (s), 720 (s), 559 (w), 491 (m), 423 (m).
1H NMR (300 MHz, CDCl3), δ [ppm]: 8.06–8.11 (d, J=7.7 Hz, 2H), 7.42–7.48 (t, J=7.5 Hz, 2H), 7.38–7.41 (d, J=8.1 Hz, 2H), 7.17–7.23 (t, J=6.5 Hz, 2H), 4.33–4.41 (q, J=7.2 Hz, 2H), 1.41–1.48 (t, J=7.2 Hz, 3H).
2-(Carbazol-9-yl)ethyl methacrylate (CEM)
A 1,2-dichloroethene solution was prepared containing: 2 (21 g, 0.098 mol), methacrylic acid (9.1 g, 0.106 mol) and 4-pyrrolidinopyridine (2.1 g, 0.02 mol, 5 wt%). A solution of DCC (2.0 g, 0.014 mol) in 90 mL of dichloromethylene was then added dropwise over 20 min. The reaction was carried out at room temperature for a further 24 h. Then, the by-product (i.e. dicyclohexylurea) formed during the reaction was separated from the solution, which was left to crystallize white crystals. Purification of the compound was made by recrystallization from ethanol. Evaluation of the progress of the reaction was carried out by means of a coupled chromatographic method GC-FID. Yield: 93 %, m.p. 81–82 °C, lit. 81.5–82.5 °C [21].
ESI-MS: m/z=280.21 [M-H]+.
1H NMR (300 MHz, DMSO), δ [ppm]: 1.79–1.82 (3H, s, CH2=C-CH3), 4.53–4.60 (4H, m, CH2–CH2), 5.45–5.49 (1H, m, trans C=CH2) 7.13–7.50 (6H, m), 8.03–8.01 (2H, m).
FTIR (KBr, [cm−1]): (3072 (w), 2949 (w), 2933 (w), 1746 (s), 1648 (m), 1569 (m), 1485 (m), 1424 (w), 1357 (w), 1294 (w).
7-Diethylaminocoumarin-3-carboxylic acid
The reaction vessel, equipped with a magnetic stirrer, was charged with 4-diethylamino-2-hydroxybenzaldehyde (1.9 g, 0.01 mol) and diethyl malonate (1.6 g, 0.01 mol). The mixture was heated for 5 min. at 130 °C in the microwave reactor (Prolabo, France) using 90 W power setting. After complete homogenization, a catalytic amount of piperidine (0.158 g, 0.002 mol) was added into the vessel. Then the synthesis was carried out for 15 min. using continuous microwave heating mode with power 150 W, reaching the temperature of 190 °C.
After cooling down, the reaction mixture was transferred into a solution containing: 50 mL of methanol and 50 mL of 0.1 M NaOH solution. The hydrolysis reaction was carried out in the microwave reactor (Ertec, Poland) using microwave heating with 150 W for a period of 30 min. The product, was then precipitated by adding the reaction mixture to distilled water and, under continuous stirring, a hydrochloric acid solution was added dropwise until pH of the solution reached 6.5. The resulting dark-yellow precipitate was filtered and dried. Purification was carried out by three recrystallizations from ethanol. The total synthesis yield was 70 %, m.p. 186–189 °C [24].
ESI-MS: m/z=280.21 [M-H]+.
1H NMR (300 MHz, DMSO), δ [ppm]: 8.44 (s, 1H), 7.47 (s, 1H), 6.61 (s, 1H), 6.52 (s, 1H), 3.65–3.44 (m, 2H), 3.39–3.17 (m, 2H), 1.23–1.17 (m, 6H).
FTIR (KBr [cm−1]): 3429 (s), 2978 (w), 2936 (w), 1737 (s), 1666 (w), 1619 (s), 1577 (w), 1513 (s), 1478 (w), 1451 (w), 1404 (m), 1356 (w), 1313 (w), 1295 (w), 1266 (w), 1208 (w), 1190 (w), 1130 (w), 1082 (w), 1008 (w), 960 (w), 830 (w), 802 (m), 477 (m).
2-(methacryloxy)ethyl ester of 7-diethylamino-coumaric-3-carboxylic acid (MK)
7-Diethylaminocoumarin-3-carboxylic acid (1.6 g, 6.0 mmol), 2-hydroxyethyl methacrylate (1.26 g, 6 mmol), 4-pyrrolidinopiperidine (0.24 g, 1.5 mmol) were dissolved in 50 mL of THF. Then a DCC solution (1.86 g. 6 mmol) in 20 mL THF was added for 0.5 h to the reaction mixture. The reaction was carried out at room temperature with stirring for 24 h. The resulting precipitate (i.e. dicyclohexylurea) was separated by filtration, and solvent was allowed to evaporate until the product precipitated as a yellow powder. Purification was carried out by recrystallization from ethanol. Yield. 84 %, m.p. 210–211 °C [24].
ESI-MS: m/z=374.12 [M-H]+.
1H NMR (300 MHz, dDMSO), δ [ppm]: 8.51 (s, 1H), 7.59 (d, J=9.0 Hz, 1H), 6.75 (d, J=9.0 Hz, 1H), 6.51 (s, 1H), 6.03 (s, 1H), 5.67 (s, 1H), 4.40 (dd, J=15.3, 5.7 Hz, 4H), 3.46 (q, J=7.0 Hz, 4H), 1.86 (s, 3H), 1.12 (t, J=7.0 Hz, 6H).
FTIR (KBr [cm−1]): 3123 (w), 2976 (s), 2932 (m), 1760 (s), 1714 (s), 1625 (s), 1586 (s), 1518 (s), 1485 (m), 1424 (m), 1357 (m), 1294 (s), 1220 (s), 1186 (s), 1176 (s), 1101 (s), 1037 (m), 962 (m), 950 (m), 857 (m), 818 (m), 795 (s), 695 (s), 523 (m), 476 (m).
5-Chloromethyl-8-hydroxyquinoline hydrochloride (CCH)
The compound was prepared according to the procedure described in literature [25]. 8-Hydroxyquinoline (23.36 g, 0.2 mol) was dissolved in concentrated HCl (200 mL) and 37 % formaldehyde solution (25.6 mL, 0.32 mol) was added dropwise over 2 h while stirring. The temperature was maintained at ca. 21 °C throughout the whole time. Then the solution was flushed for 10 h with HCl gas. After 24 h the precipitated yellow precipitate was filtered off, washed with 10 mL concentrated HCl, 3×10 mL acetone and allowed to dry under vacuum. Light yellow crystals were obtained with a yield of about 92 %, m.p. 280 °C [25].
ESI-MS: m/z=195.63 [M-H]+.
1H NMR (300 MHz. D2O), δ [ppm]: 9.12 (td, J=8.8, 1.4 Hz, 2H), 8.87 (dt, J=5.5, 1.4 Hz, 2H), 8.01–7.85 (m, 2H), 7.61 (dd, J=8.0, 3.5 Hz, 2H), 7.27 (dd, J=8.0, 1.4 Hz, 2H), –CH2Cl 3.32 (s, 2H).
FTIR (KBr [cm−1]): 3300 (–OH), 2837–2548 (s), 2023 (w), 1925 (w), 1626 (m), 1597 (s), 1562 (s), 1496 (m), 1390 (m), 1357 (m), 1307 (s), 1281 (m), 1242 (m), 1227 (w), 1154 (m), 1083 (w), 1056 (w), 1029 (m), 858 (m), 813 (m), 696 (s).
5-Methyl(2-methacryloyloxy)-8-hydroxyquinoline (QM)
In a flask equipped with a reflux condenser and magnetic stirrer, (40 g, 0.30 mol) of 2-hydroxyethyl methacrylate (HEMA), 0.4 g of hydroquinone and anhydrous sodium acetate (3.56, 4.34 mmol) were placed. The mixture was stirred at 50 °C for 1.5 h under inert atmosphere to give a suspension. Then (10 g, 0.0434 mol) CCH was added in portions and the reaction was continued at 80 °C for 2 h. After cooling down, the contents of the flask were poured into ice water and neutralized with dilute ammonia solution. Next the white precipitate was filtered, washed with large amount water and dried. Purification of the compound was carried out by crystallization from petroleum ether (medium fraction). The reaction yield was 91 %. m.p. 86–87 °C [26].
ESI-MS: m/z=288.15 [M-H]+.
1HNMR (300 MHz. CDCl3), δ [ppm]: 8.79 (dd, J=4.2, 1.5 Hz, 1H), 8.58–8.40 (m, 1H), 7.54–7.31 (m, 2H), 7.23–7.01 (m, 1H), C=CH2 6.05 (s, 1H), C=CH2 5.54 (t, J=1.6, Hz, 1H), 4.89 (s, 2H), 4.30 (t, 2H), 3.72 (t, 2H), 1.91 (s, 3H).
FTIR (KBr [cm−1]: 3300 (m), 2956 (w), 1718 (s), 1633 (m), 1613 (m), 1581 (s), 1506 (m), 1475 (m), 1384 (m), 1319 (m).
Terpolymer synthesis
In the Egertz tubes, successive amounts of three monomers are placed: CEM, QM, MK (the molar ratios of the substrates are shown in Table 1) and AIBN; 1.5 mol% of the total number of moles of monomers used. Then 7 mL of anhydrous 1,4-dioxane was added to the vessels, and, after the dissolution of the monomers, the system was purged with argon for 15 min. The tubes were finally sealed under an argon shield and placed in a thermostatic chamber where copolymerization was carried out at 50 °C for 72 h. In the next step, the polymers were precipitated in MeOH, filtered and dried. Purification was carried out by dissolving the polymers in THF and reprecipitating in MeOH.
The molar ratios of CEM, QM, MK in the reaction mixtures.
| Akronym | CEM [% mol] | QM [% mol] | MK [% mol] | Yield [%] |
|---|---|---|---|---|
| CEM-0.5QM-0.5MK | 99 | 0.5 | 0.5 | 93 |
| CEM-1QM-0.5MK | 98.5 | 1 | 0.5 | 94 |
| CEM-1QM-1MK | 98 | 1 | 1 | 93 |
| CEM-2MK-1MK | 97 | 2 | 1 | 96 |
| CEM-3QM-1MK | 96 | 3 | 1 | 92 |
| CEM-2.5QM-2.5MK | 95 | 2.5 | 2.5 | 91 |
| CEM-12QM-4MK | 84 | 12 | 4 | 88 |
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Polymerization conditions: t=72 h, T=50 °C, AIBN 1.5 % mol, Vsolvent=7 mL.
Synthesis of terpolymers containing Alq3 – CEM-QM-MK_ (Q)
The synthesis consisted of preparing solutions of terpolymers CEM, QM, MK in anhydrous THF at concentrations of ~5.6×10−4 mol/L, to which was added dropwise over 8 h, 100 mL of bis(8-hydroxy-quinoline)isopropoxylate (Alq2ispr) solution in anhydrous THF using in each case 1.5 molar stoichiometric stoichiometry of the chelate. The solutions containing Alq2ispr were prepared on the basis of previously made findings of the actual composition. After completion of the reaction, the solutions were centrifuged (20 min, 8000 rpm) to separate solid residues. The polymers were then precipitated with methanol, centrifuged and dried. The purification procedure was repeated three times.
Results and discussion
In the present work, 2-(9-carbazolyl)ethyl methacrylate (CEM) was prepared in the two-step method. The first reaction was N-alkylation of carbazole with 2-chloroethanol. The product was then subject to an esterification reaction with methacrylic acid by the activated ester method in the presence of DCC. The functional 2-(9-carbazolyl) ethyl methacrylate (CEM) monomer will be the main component of all the copolymers investigated in the paper (Fig. 1).
Synthesis of 2-(9-carbazolyl)ethyl methacrylate (CEM).
Then the preparation of 2-(methacryloxy)ethyl ester of 7-diethylamino-coumaric-3-carboxylic acid (MK) was carried out in two stages as well. In the first stage, 7-diethylaminocoumarin-3-carboxylic acid was obtained by the Knovenagel condensation reaction of 4-diethylaminosalicylaldehyde with diethyl malonate under microwave irradiation [27] followed by a hydrolysis reaction (Fig. 2).
Preparation of 7-diethylaminocoumarin-3-carboxylic acid.
7-Diethylaminocoumarin-3-carboxylic acid was then subject to an esterification reaction with 2-hydroxyethyl methacrylate by the activated ester method in the presence of DCC. The monomer 2-(methacryloxy)ethyl ester of 7-diethylamino-coumaric-3-carboxylic acid (MK) will be the component of all the copolymers described in the paper (Fig. 3).
Synthesis of 2-(methacryloxy)ethyl ester of 7-diethylamino-coumaric-3-carboxylic acid (MK).
The third monomer, 5-methyl(2-methacryloyloxy)-8-hydroxyquinoline (QM), was also prepared in two-step method. In the first step, chloroformylation of 8-hydroxyquinoline in the presence of formaldehyde/HCl was carried out to give 5-chloromethyl-8-hydroxyquinoline hydrochloride (CCH). The final step was the etherification reaction of CCH by Williamson method which resulted in 5-methyl(2-methacryloyloxy)-8-hydroxyquinoline (QM). The QM monomer was used to complex Alq3 in all the copolymers (Fig. 4).
Preparation of 5-methyl(2-methacryloyloxy)-8-hydroxyquinoline (QM).
Terpolymer containing CEM, QM, and MK were obtained by free-radical copolymerization of CEM, QM, and MK by a solution polymerization method that was used successfully for the synthesis of similar systems and coordination complexes of Alq3 [21], [28]. Molar ratios of the monomers in the reaction mixtures are shown in Table 1 (Fig. 5).
Structure of terpolymers containing CEM, QM, and MK.
Finally, the terpolymers of CEM-QM-MK containing covalently linked aluminum complexes with 8-hydroxyquinoline were prepared by the reaction of bis(8-hydroxy-quinoline)isopropoxylate (Alq2ispr) solution in anhydrous THF using in each case 1.5 molar stoichiometric stoichiometry of the chelate. The amount of the solutions containing Alq2ispr were estimated on the basis of previously made investigations of the real compositions of the terpolymers (Fig. 6).
Synthesis and structure of terpolymers of CEM-QM-MK containing Alq3.
In the literature, there examples of calculations of copolymer compositions that consists of two comonomers in the main chain [29], [30]. In the case of CEM-QM-MK terpolymers, it was possible to arrange the equation for determination of their compositions since 1NMR spectra of the mers and terpolymers are slightly different. The terpolymers are consisted of three types of mers, which structurally show considerable similarity: they contain aromatic systems. Each mer has one nitrogen atom of different chemical constitution and spacers between the rings and the methacrylic rest. The methylene bridges present in the spacers, in each case, possess an unique chemical environment in the form of strongly electron-accepting substituents: N−, RC(O)O−, RO−, as a result of which they are easily differentiated on NMR spectra of the monomers. Nevertheless, for terpolymers, these protons included in the methylene groups give the extended signals, merged into a whole and as a result are not possible to individualize.
Eventually, the compositions of the terpolymers were determined based on the analysis of 300 MHz 1HNMR spectra recorded in deuterated DMSO. In the first stage, chemical shifts for the proton signals occurring in the CEM, QM, MK spectra were thoroughly identified and the correct location on 1HNMR spectra was assigned to them. Then, using the Mestrenova® program, the appropriate spectral ranges were integrated to obtain the surface area values for the signals of the following protons:
aromatic rings in CEM, QM and MK (6.4–9.0 ppm),
hydroxyl groups in QM (9.5–10.00 ppm),
methylene groups in MK (0.67–0.87 ppm).
The most significant groups of proton signals in the range of offsets from 6.4 to 9.0 ppm gave a signal proportional to the number of protons in all the aromatic rings, but did not provide information on the molar participation of the three mers. Therefore, in 1H NMR spectra of the QM a proton signal from the OH (9.5–10.00 ppm), which was present in all 1HNMR spectra of monomer and terpolymers was used to calculate the content of QM in the terpolymers. Similarly, the signals of two methyl groups in 7-diethylamino moiety of MK (0.67–0.87 ppm) was used to calculate the content of MK in the terpolymers. The comparison of 1H NMR spectra for monomers: CEM, QM, MK and for CEM-2QM-1MK terpolymer is shown in Fig. 7.
The comparison of 1HNMR spectra for monomers: CEM, QM, MK and for CEM-2QM-1MK terpolymer. The groups and their chemical shifts are marked with color.
The compositions of the terpolymers were calculated using the Mathcad®, in which a set system of equations with three unknowns and appropriate commands adapted to the working environment of the program used are presented below. The procedure was used for the calculations of content of all the terpolymers, and the results are summarized in Table 2.
The content of CEM, QM, MK in the terpolymers calculated from NMR spectra.
| Acronym | AH(6H.MK) [j2] | ∑AHarom. [j2] | AH(OH.QM) [j2] |
1HNMRa |
||
|---|---|---|---|---|---|---|
| xCEM [%] | yQM [%] | zMK [%] | ||||
| CEM-0.5QM-0.5MK | 1155.96 | 2 07 329.00 | 124.08 | 98.90 | 0.47 | 0.63 |
| CEM-1QM-0.5MK | 840.21 | 19 693.58 | 299.28 | 98.25 | 1.19 | 0.56 |
| CEM-1QM-1MK | 1928.79 | 2 75 542.18 | 247.99 | 98.36 | 0.71 | 0.79 |
| CEM-2QM-1MK | 1199.62 | 1 99 936.69 | 489.43 | 97.28 | 1.93 | 0.93 |
| CEM-3QM-1MK | 782.57 | 1 02 428.39 | 327.77 | 96.48 | 2.54 | 0.98 |
| CEM-2.5QM-2.5MK | 1655.21 | 77 386.31 | 278.56 | 95.79 | 2.12 | 2.09 |
| CEM-12QM-4MK | 2000.12 | 61 100.39 | 321.47 | 91.74 | 4.06 | 4.20 |
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ax, y, z values calculated from 1HNMR spectra.
where
x, y, z – mole fraction of CEM, QM, MK in the terpolymers
AH(OH,QM) – proton signal area of –OH (9.65–9.87 ppm) of QM [j2].
AH(6H,MK) – area of the signal of 6 protons at 2(CH3) groups (1.13–1.30 ppm) at MK [j2].
∑AHarom. – total surface area of proton signals in the aromatic rings of CEM, QM and MK [j2].
It can be stressed that real contents of CEM, QM and MK mers in the terpolymers are in a good correlation with expected values i.e. concentration of CEM, QM and MK in reaction mixtures during polymerization. The only terpolymer in which the content of QM is much lower than expected value is CEM-12QM-4MK.
The obtained terpolymers and their complexes with Alq3 were subjected to SEC analysis on the basis of which the appropriate molecular weights and degree of polydispersity were calculated. It was observed an increase in the degree of polydispersity (PDI), Mw and Mn of the terpolymers with increase of the content of QM and MK both before and after the complexation reactions (Table 3).
Molecular weights and molecular weight distribution (PDI) of the terpolymers and their complexes with Alq3.
| Acronym |
|
|
PDI | ||||||
|---|---|---|---|---|---|---|---|---|---|
| CEM-0.5QM-0.5MK (Q) | 18 600 | 20 600 | 9100 | 8900 | 2.0 | 2.3 | |||
| CEM-1QM-0.5MK (Q) | 16 200 | 27 700 | 7200 | 11 000 | 2.2 | 2.5 | |||
| CEM-1QM-1MK (Q) | 20 400 | 28 400 | 8000 | 10 000 | 2.6 | 2.8 | |||
| CEM-2QM-1MK (Q) | 28 900 | 55 600 | 10 900 | 18 500 | 2.6 | 3.0 | |||
| CEM-3QM-1MK (Q) | 30 200 | 60 900 | 11 500 | 19 200 | 2.6 | 3.2 | |||
| CEM-2.5QM-2.5MK (Q) | 30 000 | 55 600 | 11 200 | 19 700 | 2.7 | 2.8 | |||
| CEM-12QM-4MK (Q) | 25 300 | 8900 | 2.8 | ||||||
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Green – the terpolymers; white – Alq3 complexes.
By comparing the respective mass distributions of terpolymers, it is shown that the complexation reaction increases their degree of polydispersity, which is determined by physicochemical properties of polymers and the content of QM because it forms active coordination centers capable of covalently binding Alq3 molecules.
The analysis of absorption and emission spectra was performed for THF solutions of the terpolymers after their complexation reactions with Alq3 (Fig. 8). The absorption spectra include: easily distinguishable bands having two distinct maxima in the region from 300 nm to 355 nm assigned to carbazole rings (CEM), and wide bands extending from 355 to 500 nm with one maximum at 416 nm, assigned to coumarin (MK).
Absorption and emission spectra of CEM-QM-MK terpolymers containing Alq3.
The emission spectra is shown after normalizing the remaining emission spectra against the absorption value CEM-0.5QM-0.5MK occurring at 457 nm. All the spectra were recorded using excitation source at 320 nm, which can be absorbed by CEM, QM as well as Alq3 pending groups. The emission spectrum reaches local maximum values of 352 and 365 nm due to emission of carbazole groups (CEM). Moving towards longer wavelength the most intense fluorescent band originating from the coumarin (MK) and Alq3 were recorded ca. 457 nm, which can be observed in comparison with emission spectra of the monomers (Fig. 9).
Absorption and emission spectra of monomers CEM, QM, MK and Alq2ispr (QM_Abs – absorption of QM; CEM_Abs – absorption of CEM; MK_Abs – absorption of MK; Alq2ispr_Abs – absorption of Alq2ispr; CEM_EM_Ex-320 nm – emission spectra of CEM excited at 320 nm; MK_EM_Ex_360 nm – emission spectra of MK excited at 360 nm; Alq2ispr_EM_Ex_360 nm – emission spectra of Alq2ispr excited at 360 nm. All the spectra were taken in a DMF solution – c=10−5 mol/dm3.
It is worth of stressing that the highest relative fluorescence intensity was exhibited by solutions of terpolymers containing the lowest content of MK, QM and Alq3. The maximum fluorescence shift from 453 to 461 nm was also observed along with increase of coumarin (MK) content from 0.5 to 2.5 m% in terpolymers.
Conclusions
The methods for the preparation of methacrylates containing carbazole, coumarin, and hydroxyquinoline used for the preparation of novel series of hybrid copolymers having Alq3 as pendant groups were elaborated. Moreover, syntheses of the monomers (CEM, QM, MK) consist of simple reaction procedures; the monomers CEM, QM, an MK were prepared in two-step reactions i.e. alkylation and esterification, chloromethylation and Williamson alkylation, Knoevenagel condensation and esterification, respectively. Free-radical polymerization reactions allowed obtaining a series of terpolymers with the content of QM and MK between 0.5 and 4 mol%. The fluorescence quantum yields measured in solid states with standard sample of BaMgAl10O17:Eu increase from 22 to 37 % for copolymers with coumarin (MK) content 2.5–0.5 %, respectively. Further investigation and characterization of the hybrid polymers as organic emitters are continued.
Article note
A collection of papers presented at the 17th Polymers and Organic Chemistry (POC-17) conference held 4–7 June 2018 in Le Corum, Montpelier, France.
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