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Advances in Condensed Matter Physics
Volume 2018, Article ID 9427460, 9 pages
Research Article

Synthesis and Characterization of a Multifunctional Conjugated Polymer

1Paulo Scarpa Polymer Laboratory (LaPPS), Federal University of Parana (UFPR), Curitiba 81531-970, Brazil
2São Carlos Institute of Physics (IFSC), University of São Paulo (USP), São Carlos 13566-590, Brazil

Correspondence should be addressed to Leni C. Akcelrud; moc.liamg@kainelka

Received 27 February 2018; Revised 11 April 2018; Accepted 10 May 2018; Published 7 June 2018

Academic Editor: Gary Wysin

Copyright © 2018 Emerson C. G. Campos et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This work reports the synthesis and characterization of a conjugated polymer based on fluorene and terpyridine, namely, poly[(9,9-bis(3-((S)-2-methylbutylpropanoate))fluorene-alt-6,6′-(2,2′:6′,2′′-terpyridin-6-yl)] (LaPPS71). The structure was characterized by 1H and 13C nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopy. The molar mass was measured by gel permeation chromatography (GPC). As thermal characterization, the glass transition temperature (Tg) was measured by differential scanning calorimetry (DSC). The polymer structure contains two sites capable of complexation with metallic ions, affording the possibility of obtainment of independent or electronically coupled properties, depending on the complexation site. The photophysical properties were fully explored in solution and solid state, presenting ideal results for the preparation of various metallopolymers, in addition to potential application as a metamaterial, due to the presence of the chiral center in the side chains of the polymer.

1. Introduction

In the last decades semiconducting polymers have emerged as promising structures with a wide range of photonic and electronic applications, such as flexible light-emitting displays, sensors for a variety of purposes, and solar panels, among many others [1, 2]. Their main advantages encompass the combination of semiconducting properties with the ease of processing, flexibility, and lightweight characteristics of polymer materials [25]. Nowadays, a new class has emerged which apart from the mentioned features also add metallic properties to the system [6]. This new class, the metallopolymers, are composed by a conjugated polymer backbone containing a metallic center that can occur in three main configurations, according to Wolf’s classification [7]: the metallic center is attached to a ramification of the main chain (Type I) coordinated directly to a ligand which is part of the repeating unit of the polymer (Type II) or still can be itself a monomeric unit of the polymer (usually as a co-monomer), (Type III). This way, metallic properties arise such as optical, magnetic, electrochromism and new paths for light emission, to mention the most relevant. The optical properties of these systems may or may not be a result of electronic coupling between the metal and the conjugated backbone, and each possibility offers a set of advantages [710]. It is worth mentioning that in Type III ill-defined structures may result due to the possibility of chain growth in several directions that are associated with the coordination state of the metal, leading to ramifications and crosslinking [8].

In this paper we report on the synthesis and characterization of a precursor to a metallopolymer, which apart from adequate site for metal insertion, also bears a chiral center. This characteristic has been used to produce chiro-optical materials that represent a new class of polymers with very special behavior, giving rise to the obtainment of exceptional electromagnetic properties. The applications of chiral polymers are wide, allowing the manipulation of electromagnetic radiations for the achievement of superlenses, electromagnetic invisibility (invisibility cloak), and super-resolution in optical images [11, 12], as examples. The most representative parameter to characterize a chiro-optical material is the chirality parameter (), which can be measured by various means [13, 14].

The material explored here contains a twofold functionality; it can be used to prepare a metallopolymer or a chiro-optical material. The structure, an alternated copolymer of fluorene and terpyridine, namely, poly[(9,9-bis(3-((S)-2-methylbutylpropanoate))fluorene-alt-6,6′-(2,2′:6′,2′′-terpyridin-6-yl)] (LaPPS71), is depicted in Figure 1.

Figure 1: Structure of LaPPS71.

The complexation with metals can be performed according to two paths, one uses the ester site or alternatively the terpyridine moiety. This last one is straightforward and can be accomplished as described elsewhere [9]. The resulting complexed product belongs to Type II. The tridentate ligand is one of the most used for the preparation of lanthanide complexes [9, 1517]. Alternatively, a Type I could be also prepared by using the ester group pendant to the main chain. The ester site needs a conventional hydrolysis process to afford a carboxylic acid [18, 19], providing the site for the insertion of the metal [20, 21].

2. Materials and Methods

2.1. Materials

Potassium carbonate (Vetec, 99%), 6,6′′-dibromo-2,2′:6′,2′′-terpyridine (Aldrich, 90%), 2,7-bis(4,4′,5,5′-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis(3-((S)-2 methylbutylpropanoate))fluorene, tetrakis(triphenylphosphine)palladium(0) (Aldrich, 99%), and sodium hydroxide (Biotec, P. A.) were used. Dichloromethane (Synth, 99.5%), tetrahydrofuran (Synth, 99.8%), chloroform (Vetec, P.A.), ethyl acetate (Synth, 99.5%), toluene (Aldrich, 99.3%), methanol (Aldrich, 99.6%.), and ethanol (Synth, 99.5%) were used. Deuterated chloroform, containing 1% (v/v) TMS (Sigma-Aldrich, P.A.) as standard for the NMR analyses, was used. For purification, a chromatographic column, 15 cm in height and 2 cm diameter, with silica as a stationary phase, was used.

2.2. Equipment

The structural characterization of the polymer was performed by 1H and 13C NMR spectroscopy, recorded on a Varian Inova-400 Instrument (399.65 MHz for 1H, 100.40 MHz for 13C) using polymer solutions containing deuterated chloroform (CDCl3) and TMS as reference. The simulated data for 1H NMR and 13C NMR were obtained by ChemDraw Ultra 12.0 software. The FTIR spectra were acquired using KBr pellets with the BOMEM (Hartmann & Braun) MB-Series equipment scanning rate of 4000 – 400 cm–1 and 24 scans/min. The molar mass of polymer was determined by gel permeation chromatography (GPC) using polystyrene as standards and THF as eluent at 1 mL/min flow rate in an Agilent 1100 liquid chromatography system with Plgel Mixed-B and Mixed-C columns. Thermal characterization was performed by DSC technique and was measured on a Netzsch DSC 204 F1. All samples were heated from 20 to 200°C in a nitrogen atmosphere and then cooled to 20 at 10°C min−1 with scanning of the 10°C min−1 and nitrogen flow 15 ml · min−1. UV-Vis spectra were measured on a Shimadzu UV-3101PC spectrometer. Emission spectra were acquired with on a Shimadzu RF–5301PC spectrophotometer in THF solution. The UV-Vis and emission measurements were performed in THF solution.

2.3. Synthesis of the Polymer

The LaPPS71 was synthesized via Suzuki coupling. The synthesis and structural characterization of the chiral monomer precursor were shown in an earlier work published by our group [13]. The general procedure for the synthesis of LaPPS71 was the following: 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis(3-((S)-2-methylbutyl propanoate))fluorene (0.2 g, 0.285 mmol) and 6,6′′-dibromo-2,2′:6,2′′-terpyridine (0.123 g, 0.314 mmol) were added to a 2 mol · L–1 solution of K2CO3 (12 mL) and toluene (36 mL). The mixture was subjected to argon atmosphere. After 30 minutes, tetrakis(triphenylphosphine)-palladium(0) (0.02 g, 0.017 mmol) was added to the mixture and the temperature adjusted at 110°C. The reaction proceeded under constant stirring for 48 hours. After that, the organic phase was separated from the aqueous one and the product was extracted and washed three times with chloroform. The organic phase was separated from the aqueous one and the product was extracted and washed three times with chloroform. The product of the reaction was mixed with anhydrous MgSO4 for retention of water traces. Subsequently, the product was purified in a chromatography column using silica as the stationary phase and as mobile phase a combination of dichloromethane/ethyl acetate (4:1) was used. At the end of the procedure the solvent was removed to give 141 mg of pale yellow solid with a 72.2 % yield. 1H NMR (CDCl3, δ): 8.87–8.23 (m, 8H); 8,22–8,10 (m, 1H); 8.08–7.88 (m, 6H) 3.85–3.60 (m, 4H); 2.90–2.49 (s, 4H); 1.93–1.67 (s, 4H); 1.35–1.17 (m, 6H); 0.84–0.72 (t, 12H). 13C NMR (CDCl3, δ): 173.58; 156.26; 156.02; 155.41; 148.98; 141.81; 139.18; 137.95; 137.75; 136.86; 127.08; 127.05; 121.45; 120.72; 120.53; 69.08; 54.07; 33.93; 29.70; 29.10; 25.90; 16.30; 11.10. For solid state studies, these films were prepared via spin-coating at 1100 rpm using chloroform/chlorobenzene (10:1 v/v) solutions, at 10 mg · mL–1, which were annealed at 25°C, 100°C, 150°C, 175°C, and 200°C, in a vacuum oven for 2 h.

2.4. Computational Methods

The optimized geometry and frontier levels of the tetramer structure of alternated fluorene and terpyridine copolymer (LaPPS71) were simulated with density functional theory (DFT), using Becke, Three-Parameter, Lee–Yang–Parr functional B3LYP [22] functional, with 6-311G(d, p) split-valence basis set. Tetramer geometries were used because they represent satisfactorily the effective conjugation length for this kind of structure [23]. The structure was submitted to a vibrational analysis, and no imaginary frequency modes were obtained. Based on the optimized structure, the electronic spectra calculation was performed using ZINDO/S (Zerner’s Intermediate Neglect of Differential Overlap/Single) parametrization, using the first three singlet excited states, and the transition energies were weighted by the oscillator strength values (f) in the study of organic compounds [24]. All simulations were performed using GAUSSIAN 09 program [25].

3. Results and Discussion

3.1. Synthetic Route

The synthesis followed the Suzuki cross-coupling polycondensation as described in detail above and is illustrated schematically in Figure 2.

Figure 2: Synthesis route for LaPPS71.
3.2. Structural Characterization

The molar mass of LaPPS71 was determined by GPC method, presenting values of = 18000 g · mol–1 and polydispersity (PDI) of 1.9. DSC runs gave for glass transition temperature the value of 98°C. The material presented good solubility in common organic solvents as chloroform, THF, and dichloromethane. Figure 3 shows the most significant FTIR absorptions, which can be associated with the stretching (), asymmetric stretch (), symmetric stretching (), and out-of-plane deformation (). In the range 1426 and 1561 cm−1, related to ν(CC; CN) bond is attributed to the terpyridine groups [9, 26, 27]. The band at 794 cm−1 is associated with the (C—H) p-substituted ring of the fluorene group and 2947 cm−1 refers to (C—H) sp2 [28]. All those bands are attributed to chemical species absorption in the aromatic region of the polymer structure. The strong band at 1730 cm−1 is characteristic of the (C=O) of the ester group of the alkyls [29]. There is also the ν(C—O) bond at 1160 cm−1 and 2873 cm−1 attributed to the (C—H) sp3 of the polymer [26, 29]. These absorptions belong to the aliphatic chain of the structure.

Figure 3: FTIR spectrum (KBr) of LaPPS71.

1H and 13C NMR analyses of the polymer were also performed. Figure 4 shows the 1H NMR spectrum of the structure, in which the numbers in the polymer chain of the spectrum correspond to the hydrogen atoms for the corresponding carbon atom.

Figure 4: Assigned 1H NMR spectrum of LaPPS71.

Table 1 shows the chemical shifts observed in the 1H NMR spectrum, as well as the simulated and experimental integrations correlated to the polymer structure. The upfield region between 0.72 to 3.85 ppm refers to the hydrogen atoms bonded to the aliphatic carbon atoms from 1 to 7. The chemical shifts seen for the protons of the carbon atoms 5 and 6 are due to the inductive effect of the oxygen atom, strongly electronegative element. Hydrogen atoms of the aromatic chain absorb energy in a magnetic downfield with signs in the region between 7.88 and 8.87 ppm [26, 28, 3032].

Table 1: Chemical shifts of 1H NMR of the LaPPS71.

The polymer structure was also confirmed by the 13C NMR spectrum, shown in Figure 5, in which the singlet signals stand for the chemical shifts at 137.95 and 136.86 ppm, related to the carbon atoms 1 of the fluorene (see the polymer’s structure in the figure). According to the simulated structure of the precursor monomer, the equivalent peaks to carbon atoms 1 would have chemical shifts at 130.9 ppm. The carbon atoms 2 highlighted in the terpyridine showed peaks in the range between 155.41 and 156.26 ppm of the spectrum, while those of the unpolymerized simulated structure possess chemical shifts at 143.1 ppm [26, 27, 32]. A more detailed and accurate analysis of the IR and NMR data about conjugated polymers can be done as described in previous literature [33].

Figure 5: 13C NMR spectrum of the LaPPS71, aromatic region.
3.3. Photoluminescence Studies

Photophysical studies were performed in THF solutions and film form. Figure 6 shows the absorption spectra in a range of concentrations at room temperature, in which the main bands were seen at 245 nm and 345 nm. For solutions, those bands can be related to the π-π transitions, composed by the pyridine-fluorene-pyridine chromophore, as supported by theoretical calculations.

Figure 6: Absorption spectra of LaPPS71 in solution and solid state.

Theoretical calculations were performed to study the nature of the electronic transitions involved. Table 2 brings the results obtained by the DFT calculations.

Table 2: Calculation data for the electronic structure of the LaPPS71.

The calculated absorption spectra are characterized by two main contributions at 352 nm and 364 nm, associated with the 250 nm and 350 nm empirically observed. The transitions are mainly characterized as of the π-π type, in which the main chromophore in all transitions is composed of pyridine-fluorene-pyridine unit. The first one (352 nm) is associated with the transition HOMO-2→LUMO, which occurs between orbitals presenting in the same atoms, while the other transition, HOMO-1→LUMO+1, takes place between different segments of the chain. Figure 7 brings the compositions of the frontier orbitals of LaPPS71 obtained by the calculations. It is noteworthy that more accurate results could have been obtained using the TD-DFT method instead of the semiempirical ZINDO/S [34]. Nevertheless, the former was chosen because it is computationally more rapid, giving a satisfactory cost/benefit ratio, considering the quality of results required for the polymer characterization here.

Figure 7: Selected frontier orbitals of the LaPPS71 tetramer with hydrogen atoms omitted.

It is possible to verify that the conjugation is confined to the segment pyridine-fluorene-pyridine. This is accounted for the terpyridine unit mobility, which can adopt different conformations, breaking the chain conjugation. According to the literature [35] three different conformations can be assigned to this group: cis-cis, trans-trans and cis-trans which in turn would result in changes of the energy levels in the excited state, depending on the chemical environment.

The emission spectra run in THF solutions of various concentrations and in the solid state at room temperature are shown in Figure 8. The spectra are characterized by three bands: the first two show a well-defined profile peaking at 370 nm and 380 nm, whereas the third one covers the 390-500 nm range, depending on the concentration. The first band decreases in intensity and redshifts with increasing concentration. The opposite trend is observed for the second band: for 10−6, 10−5, and 10−4 mol · L−1 solutions, the position of the transition does not change, but intensity increases substantially, indicating an increase in the concentration of emitting units. When the concentration attains 10−3 mol · L−1 a redshift is clearly observed. This behavior can be attributed to the formation of intermolecular excited states brought about by π- π stacking, leading to the formation of new ππ excitation bands, consequently lowering the band gap [36, 37]. The decrease of the bands intensity with increases in solution concentration is accounted to the inner-filter effect (IFE), important phenomenon in fluorescence, which basically occurs due the reabsorption of the emitted light by the fluorophore itself, thus decreasing the intensity of emission [38]. Additionally, the shoulder presented at 420 nm in all samples turns progressively more evident with concentration increases. In the solid state, the first band is suppressed, and the second one predominates, presenting a broadening on the shoulder, which seems to envelop various emitting states, corresponding to the various conformational states of the chain, mainly due to the terpyridine group.

Figure 8: Spectra of the light-emitting of the polymer LaPPS71 in different concentrations of solution and solid state ( = 345 nm).

The emitting profile of LaPPS71 makes the polymer an excellent material for lanthanide complexation, especially Eu and Tb ions [9, 39]. The ligands associated with these ions generally are chromophores capable of sensitizing of the lanthanide light emission. β-diketones, for example, absorb energy in a region of the ultraviolet-visible and then transfer efficiently to the lanthanide, via intersystem crossing process. This mechanism, called the “antenna effect” [39, 40], could be explored here, since the polymer emits in the same region where the chromophore compound linked to the metal is absorbed [68].

The effect of thermal annealing was also studied to see how the photophysical properties would be affected using this treatment. The results are shown in Figure 9(a) for absorption and Figure 9(b) for emission.

Figure 9: Absorption (a) and emission (b) of annealed samples of LaPPS71 ( = 345 nm).

The annealing temperatures were varied in the range 25°C to 200°C. The higher absorption and emission intensities were obtained around 100°C. This result is expected, bearing in mind that this value is near to (98°C), and was attributed to the long range segmental motion acquired around this point, helping the chains to get close to each other and thus accommodating the π-π stacking state [13, 41]. It is noteworthy that the spectra profiles of absorption and emission did not change, indicating that the number of stacked chains increased, or the size of the stacks also increased, but their length (meaning the length of the associated packs) attained an equilibrium. Otherwise the conjugation length would be larger and a bathochromic shift would be observed.

4. Conclusions

The synthesis and characterization of a novel conjugated polymer based on fluorene and terpyridine were described. The photophysical properties of the material were exploited and their structure confirmed by NMR and FTIR spectroscopy. The structure is a promising conjugated polymer, providing the multifunctional properties of an emitting material, presenting at the same time the possibility of complexation with metallic ions in two configurations. Moreover, the chiral center in the polymer side chain could provide a useful material for several applications in the field of optoelectronics.

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.


The authors wish to acknowledge INEO (National Institute for Organic Electronics) CAPES (Coordination for the Improvement of Higher Education Personnel) for financial support, UFPR (Federal University of Parana), and PIPE (Materials Science and Eng. Graduate Program).


  1. X. Guo, M. Baumgarten, and K. Müllen, “Designing π-conjugated polymers for organic electronics,” Progress in Polymer Science, vol. 38, no. 12, pp. 1832–1908, 2013. View at Publisher · View at Google Scholar · View at Scopus
  2. L. Dou, Y. Liu, Z. Hong, G. Li, and Y. Yang, “Low-Bandgap Near-IR Conjugated Polymers/Molecules for Organic Electronics,” Chemical Reviews, vol. 115, no. 23, pp. 12633–12665, 2015. View at Publisher · View at Google Scholar · View at Scopus
  3. L. Lan, G. Zhang, Y. Dong, L. Ying, F. Huang, and Y. Cao, “Novel medium band gap conjugated polymers based on naphtho[1,2-c:5,6-c]bis[1,2,3]triazole for polymer solar cells,” Polymer (United Kingdom), vol. 67, pp. 40–46, 2015. View at Publisher · View at Google Scholar · View at Scopus
  4. Z. Lu, J. Zhang, C. Li, F. Feng, and Z. Bo, “The effect of meta-substituted or para-substituted phenyl as side chains on the performance of polymer solar cells,” Synthetic Metals, vol. 220, pp. 402–409, 2016. View at Publisher · View at Google Scholar · View at Scopus
  5. X. Wang, Q. Su, Y. Li et al., “Synthesis and photovoltaic properties of donor – acceptor conjugated silole,” Synthetic Metals, vol. 220, pp. 433–439, 2016. View at Google Scholar
  6. G. Taupier, M. Torres-Werlé, A. Boeglin et al., “Optically active sum-frequency generation as an advanced tool for chiral metallopolymer material,” Applied Physics Letters, vol. 110, no. 2, Article ID 021904, 2017. View at Publisher · View at Google Scholar · View at Scopus
  7. M. O. Wolf, “Recent advances in conjugated transition metal-containing polymers and materials,” Journal of Inorganic and Organometallic Polymers and Materials, vol. 16, no. 3, pp. 189–199, 2006. View at Publisher · View at Google Scholar · View at Scopus
  8. J. M. Stanley and B. J. Holliday, “Luminescent lanthanide-containing metallopolymers,” Coordination Chemistry Reviews, vol. 256, no. 15-16, pp. 1520–1530, 2012. View at Publisher · View at Google Scholar · View at Scopus
  9. D. A. Turchetti, M. M. Nolasco, D. Szczerbowski, L. D. Carlos, and L. C. Akcelrud, “Light emission of a polyfluorene derivative containing complexed europium ions,” Physical Chemistry Chemical Physics, vol. 17, no. 39, pp. 26238–26248, 2015. View at Publisher · View at Google Scholar · View at Scopus
  10. W. Feng, Y. Zhang, Z. Zhang et al., “Near-infrared (NIR) luminescent metallopolymers based on Ln4(Salen)4 nanoclusters (Ln = Nd or Yb),” Journal of Materials Chemistry C, vol. 2, no. 8, pp. 1489–1499, 2014. View at Publisher · View at Google Scholar · View at Scopus
  11. H.-T. Chen, W. J. Padilla, M. J. Cich, A. K. Azad, R. D. Averitt, and A. J. Taylor, “A metamaterial solid-state terahertz phase modulator,” Nature Photonics, vol. 3, no. 3, pp. 148–151, 2009. View at Publisher · View at Google Scholar · View at Scopus
  12. B.-X. Wang, X. Zhai, G.-Z. Wang, W.-Q. Huang, and L.-L. Wang, “A novel dual-band terahertz metamaterial absorber for a sensor application,” Journal of Applied Physics, vol. 117, no. 1, Article ID 014504, 2015. View at Publisher · View at Google Scholar · View at Scopus
  13. B. Nowacki, H. Oh, C. Zanlorenzi et al., “Design and synthesis of polymers for chiral photonics,” Macromolecules , vol. 46, no. 18, pp. 7158–7165, 2013. View at Publisher · View at Google Scholar · View at Scopus
  14. A. Baev and P. N. Prasad, “Chiral polymer photonics,” Optical Materials Express , vol. 7, no. 7, pp. 2432–2439, 2017. View at Publisher · View at Google Scholar · View at Scopus
  15. A. M. W. Cargill Thompson, “The synthesis of 2,2:6,2-terpyridine ligands - Versatile building blocks for supramolecular chemistry,” Coordination Chemistry Reviews, vol. 160, pp. 1–52, 1997. View at Publisher · View at Google Scholar · View at Scopus
  16. M. A. Halcrow, “The synthesis and coordination chemistry of 2,6-bis(pyrazolyl)pyridines and related ligands - Versatile terpyridine analogues,” Coordination Chemistry Reviews, vol. 249, no. 24, pp. 2880–2908, 2005. View at Publisher · View at Google Scholar · View at Scopus
  17. A. De Bettencourt-Dias, S. Bauer, S. Viswanathan, B. C. Maull, and A. M. Ako, “Unusual nitro-coordination of europium(III) and terbium(III) with pyridinyl ligands,” Dalton Transactions, vol. 41, no. 36, pp. 11212–11218, 2012. View at Publisher · View at Google Scholar · View at Scopus
  18. A. R. Ramya, D. Sharma, S. Natarajan, and M. L. P. Reddy, “Highly luminescent and thermally stable lanthanide coordination polymers designed from 4-(Dipyridin-2-yl)aminobenzoate: Efficient energy transfer from Tb3+ to Eu3+ in a mixed lanthanide coordination compound,” Inorganic Chemistry, vol. 51, no. 16, pp. 8818–8826, 2012. View at Publisher · View at Google Scholar · View at Scopus
  19. A. Helal, S. H. Kim, and H.-S. Kim, “A highly selective fluorescent turn-on probe for Al3+ via Al3+-promoted hydrolysis of ester,” Tetrahedron, vol. 69, no. 30, pp. 6095–6099, 2013. View at Publisher · View at Google Scholar · View at Scopus
  20. A. Balamurugan, M. L. P. Reddy, and M. Jayakannan, “Single polymer photosensitizer for Tb3+ and Eu3+ ions: An approach for white light emission based on carboxylic-functionalized poly(m-phenylenevinylene)s,” The Journal of Physical Chemistry B, vol. 113, no. 43, pp. 14128–14138, 2009. View at Publisher · View at Google Scholar · View at Scopus
  21. J. J. Henkelis, T. K. Ronson, and M. J. Hardie, “Lanthanide coordination polymers with pyridyl-N-oxide or carboxylate functionalised host ligands,” CrystEngComm, vol. 16, no. 18, pp. 3688–3693, 2014. View at Publisher · View at Google Scholar · View at Scopus
  22. C. Lee, W. Yang, and R. G. Parr, “Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density,” Physical Review B: Condensed Matter and Materials Physics, vol. 37, no. 2, pp. 785–789, 1988. View at Publisher · View at Google Scholar · View at Scopus
  23. C. Zanlorenzi and L. Akcelrud, “Theoretical studies for forecasting the power conversion efficiencies of polymer-based organic photovoltaic cells,” Journal of Polymer Science Part B: Polymer Physics, vol. 55, no. 12, pp. 919–927, 2017. View at Publisher · View at Google Scholar · View at Scopus
  24. C. Zanlorenzi, S. M. Cassemiro, I. R. Grova, and L. Akcelrud, “Photophysical behavior of block copolymers containing EDOT, thiophene, and benzodiathiazole units linked to fluorene,” Journal of Polymer Science Part B: Polymer Physics, vol. 54, no. 9, pp. 908–915, 2016. View at Publisher · View at Google Scholar · View at Scopus
  25. M. J. Frisch, G. W. Trucks, H. B. Schlegel et al., Gaussian 09, 2009.
  26. Z. Demircioğlu, A. E. Yeşil, M. Altun, T. Bal-Demirci, and N. Özdemir, “X-ray structure determination, Hirshfeld surface analysis, spectroscopic (FT-IR, NMR, UV–Vis, fluorescence), non-linear optical properties, Fukui function and chemical activity of 4-(2,4-dimethoxyphenyl)-2,2:6,2-terpyridine,” Journal of Molecular Structure, vol. 1162, pp. 96–108, 2018. View at Publisher · View at Google Scholar
  27. M. Klessinger, Angewandte Chemie International Edition, Wiley, New York, NY, USA, 7 edition, 1968. View at Publisher · View at Google Scholar
  28. D. L. Pavia, G. M. Lampman, and G. S. Kriz, Introduction to Spectroscopy. A Guide for Students or Organic Chemistry, 3rd edition, 2001.
  29. A. M. Gumel, M. S. M. Annuar, and T. Heidelberg, “Growth kinetics, effect of carbon substrate in biosynthesis of mcl-PHA by Pseudomonas putida Bet001,” Brazilian Journal of Microbiology, vol. 45, no. 2, pp. 427–438, 2014. View at Publisher · View at Google Scholar · View at Scopus
  30. W.-J. Li, B. Liu, Y. Qian et al., “Synthesis and characterization of diazafluorene-based oligofluorenes and polyfluorene,” Polymer Chemistry, vol. 4, no. 6, pp. 1796–1802, 2013. View at Publisher · View at Google Scholar · View at Scopus
  31. J.-J. Wang, Y.-N. Zhou, P. Wang, and Z.-H. Luo, “The synthesis and enhancement of the surface properties of polyfluorene-based photoelectric materials by introducing fluoromonomers,” RSC Advances, vol. 3, no. 15, pp. 5045–5055, 2013. View at Publisher · View at Google Scholar · View at Scopus
  32. J. Ding, M. Day, G. Robertson, and J. Roovers, “Synthesis and characterization of alternating copolymers of fluorene and oxadiazole,” Macromolecules , vol. 35, no. 9, pp. 3474–3483, 2002. View at Publisher · View at Google Scholar · View at Scopus
  33. G. V. Baryshnikov, V. A. Minaeva, B. F. Minaev, V. Sun, and M. Grigoras, “Analysis of the electronic, IR, and 1H NMR spectra of conjugated oligomers based on 4,4-triphenylamine vinylene,” Optics and Spectroscopy, vol. 121, no. 3, pp. 348–356, 2016. View at Publisher · View at Google Scholar
  34. L. L. G. Justino, M. Luísa Ramos, P. E. Abreu et al., “Structural and electronic properties of poly(9,9-dialkylfluorene)-based alternating copolymers in solution: An NMR spectroscopy and density functional theory study,” The Journal of Physical Chemistry C, vol. 117, no. 35, pp. 17969–17982, 2013. View at Publisher · View at Google Scholar · View at Scopus
  35. D. Li, Q. Zhang, P. Wang et al., “Studies of the isomerization and photophysical properties of a novel 2,2:6,2-terpyridine-based ligand and its complexes,” Dalton Transactions, vol. 40, no. 32, pp. 8170–8178, 2011. View at Publisher · View at Google Scholar · View at Scopus
  36. U. Lemmer, S. Heun, R. F. Mahrt et al., “Aggregate fluorescence in conjugated polymers,” Chemical Physics Letters, vol. 240, no. 4, pp. 373–378, 1995. View at Publisher · View at Google Scholar · View at Scopus
  37. S. M. Cassemiro, C. Zanlorenzi, T. D. Z. Atvars, G. Santos, F. J. Fonseca, and L. Akcelrud, “Light emitting mechanisms in an alternated fluorene EDOT copolymer - A theoretical and photophysical study,” Journal of Luminescence, vol. 134, pp. 670–677, 2013. View at Publisher · View at Google Scholar · View at Scopus
  38. A. V. Fonin, A. I. Sulatskaya, I. M. Kuznetsova, and K. K. Turoverov, “Fluorescence of dyes in solutions with high absorbance. Inner filter effect correction,” PLoS ONE, vol. 9, no. 7, Article ID e103878, 2014. View at Publisher · View at Google Scholar
  39. D. Singh, K. Singh, S. Bhagwan et al., “Preparation and photoluminescence enhancement in terbium(III) ternary complexes with B-diketone and monodentate auxiliary ligands,” Cogent Chemistry, vol. 2, no. 1, 2016. View at Publisher · View at Google Scholar
  40. L. Armelao, S. Quici, F. Barigelletti et al., “Design of luminescent lanthanide complexes: from molecules to highly efficient photo-emitting materials,” Coordination Chemistry Reviews, vol. 254, no. 5-6, pp. 487–505, 2010. View at Publisher · View at Google Scholar · View at Scopus
  41. B. Nowacki, C. Zanlorenzi, A. Baev, P. N. Prasad, and L. Akcelrud, “Interplay between structure and chiral properties of polyfluorene derivatives,” Polymer (United Kingdom), vol. 132, pp. 98–105, 2017. View at Publisher · View at Google Scholar · View at Scopus