Helical Conjugated Ladder Polymers: Tuning the Conformation and

Article Cite This: Macromolecules XXXX, XXX, XXX-XXX

pubs.acs.org/Macromolecules

Helical Conjugated Ladder Polymers: Tuning the Conformation and Properties through Edge Design Maxime Daigle and Jean-François Morin* Département de Chimie and Centre de Recherche sur les Matériaux Avancés, Université Laval, 1045 Avenue de la Médecine, Québec City, Québec G1V 0A6, Canada S Supporting Information *

ABSTRACT: Two helical conjugated ladder polymers (CLPs) have been synthesized using the photochemical cyclodehydrochlorination (CDHC) reaction on polychlorinated polymer derivatives. UV−vis and photoluminescence spectroscopy revealed that the outer chlorinated rings (phenyl or thiophene) used for the ladderization step have a significant impact on the conformation and electronic properties of the resulting polymers. The thiophene-embedded CLP exhibits strong intermolecular interactions and excimer-like emission due to a loose coil conformation while the all-phenyl CLP exhibits a tightly packed coil conformation. The helical CLPs also show good affinity toward HiPco carbon nanotubes (CNTs) as stable dispersions were prepared.

■

INTRODUCTION Conjugated ladder polymers (CLPs) are well-known to adopt a planar, rigid conformation that allows optimal π-electron delocalization along the polymer backbone.1 The planarization of a dihedral angle between the monomeric units leads to conjugated polymers with lower bandgap, better solid-state organization, and enhanced stability compared to their noncyclized precursors.2−9 Although the CLP approach may seem ideal for the planarization of conjugated polymer backbone, it is much less popular than other methods such as the use of weak intramolecular H-bonding10 and heteroatoms interactions.11 Yet, the covalent bonds that hold the monomeric units in the same plane in the case of CLPs are much stronger, leading to more kinetically and thermodynamically stable materials. One of the main reasons for the lack of interest in the CLP strategy is the rather small number of efficient cyclization reactions that could be used to lock the planar structure through covalent bonds. Because the “ladderization” reactions are mostly performed on a polymeric precursor, clean, highyielded reactions are needed to avoid structural defects. Up to now, cyclization methods including Friedel−Crafts,12 metalcatalyzed cyclization of alkyne,13 carbonyl olefination,14 Mallory reaction,15 amine−carbonyl (Schiff base) condensation,16 and, more recently, ruthenium-catalyzed olefin metathesis17 have been used to prepare CLPs. While valuable, some of these methods use harsh conditions while others necessitate the use of specific functional groups that can be difficult to install on the monomers prior to the polymerization. Thus, the development of new ladderization methods is needed to expand the chemists’ toolbox and to make the CLP strategy an attracting one for the synthesis of rigid, low-bandgap polymers. © XXXX American Chemical Society

We report herein the use of the photochemical cyclodehydrochlorination (CDHC) reaction as an efficient tool for the synthesis of two helical CLPs with either phenyl (L-P1) or thiophene (L-P2) rings in the outer edge (Figure 1). The CDHC reaction, involving a 6π electrocyclization mechanism, is convenient for the straightforward synthesis of CLPs since it is performed in mild conditions without the use of a base, acid, or metal and only requires the presence of chlorine atoms on one of the monomers. We have shown in previous reports that this reaction proceeds quite fast without side-reaction.18,19 To the best of our knowledge, only a few examples of helical CLPs have been reported.20−23 The CLPs have been characterized using 1H NMR, FT-IR, UV−vis, and photoluminescence spectroscopy. Because of their rigid helical shape, the two CLPs successfully dispersed HiPco single-wall carbon nanotubes (SWCNTs), and the resulting composites have been characterized by Raman and fluorescence spectroscopy. Surprisingly, the nature of the outer ring has a tremendous impact on the conformation and properties of the CLPs.

■

RESULTS AND DISCUSSION The synthesis of the CLPs is shown in Scheme 1. Starting from 1,3-dibromo-4,6-diiodobenzene, alkylated phenyls and thiophenes were installed using chemoselective Suzuki−Miyaura coupling to yield compounds 1 and 3, respectively. Then, a double borylation on the bromine positions provided the monomers 2 and 4 according to a previously reported procedure.24 Polymerization of monomers 2 and 4 with 2,3Received: August 10, 2017 Revised: November 10, 2017

A

DOI: 10.1021/acs.macromol.7b01722 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Figure 1. Structure of the conjugated ladder polymers (a) L-P1 and (b) L-P2.

Scheme 1. Synthesis of L-P1 and L-P2

125 °C. These reaction conditions are necessary to efficiently remove oxygen and the hydrochloric acid formed during the CDHC reaction that could lead to side reactions.18 Heated solutions of P1 and P2 were then irradiated with an argon flow for 48 h with low-pressure mercury lamps at 254 and 308 nm, respectively. The irradiation wavelength has been selected to maximize the light absorption of the respective precursor. Upon irradiation, solutions of P1 and P2 underwent dramatic color change, from colorless to yellow for L-P1 and from light yellow to deep orange for L-P2, indicating a significant modification of

dichloro-1,4-diiodobenzene25 and Pd2dba3/SPhos as catalyst system afforded polychlorinated precursors P1 and P2 with 90% and 87% yield, respectively. As reported previously, these reaction conditions are mild, highly selective for C−I bond vs C−Cl bond upon oxidative addition, and especially effective to prepare poly(m-phenylenes)s with few defects.26,27 As for the ladderization procedure, P1 and P2 were dissolved in anhydrous decalin at a concentration of 0.002 M in a dried round-bottom quartz flask. Prior to irradiation, both polymer solutions were degassed with an argon stream and heated to B


Article

Macromolecules

Figure 2. Molecular structures of L-P1 (a, top view; b, side-view) and L-P2 (c, top view; d, side view). Hydrogen atoms have been omitted for clarity.

Figure 3. (a) (top) 1H NMR spectra of the chlorinated poly(m-phenylene) P1 precursor (298 K) and (bottom) L-P1 (333 K). (b) (top) 1H NMR spectra of the chlorinated poly(m-phenylene) P2 precursor (383 K) and (bottom) L-P2 (383 K).

the π-conjugation along the polymer chains. After purification, yellow and orange solids were obtained for L-P1 and L-P2,, respectively. High-temperature size-exclusion chromatography (SEC) was conducted on both precursors and irradiated polymers using polystyrene standards and 1,3,4-trichlorobenzene as eluent. As depicted in Figure S13, P1 exhibits a bimodal molecular weight distribution with a value Mn of 9800 g/mol, corresponding to a degree of polymerization (DP) of 14 and a polydispersity index (PDI) of 1.7. We hypothesize that the lower mass distribution peak centered at 15.5 min is the result of oligo-(m-phenylene) produced during the polymerization.26 On the other hand, LP1 (Figure S14) shows a slightly lower Mn value (9400 g/mol, PDI = 2.2) than P1 due to the loss of HCl molecules and a contraction of the polymer backbone upon cyclization.18,28 Compared to P1, P2 exhibits a rather broad unimodal peak and higher molecular weight with a Mn value of 11 100 g/mol and a higher polydispersity index of 2.6. From Figure S15, it is somewhat difficult to confirm whether the formation of small

oligomers occurred or not, as we suspect for P1. Once irradiated, L-P2 shows a larger Mn value (12 200 g/mol) than its precursor P2, which is in contradiction with the observation made previously for L-P1. One could think that both ladder polymers adopt the same conformation in solution, but due to thiophene-annulated backbone, a five-membered ring, L-P2 is subjected to a higher strain upon cyclization. This forces the polymers to stretch longitudinally, as calculated by molecular mechanic, and average dihedral angles of the bay regions located along the inner edge of the coils are higher for L-P2 (14.6°) than L-P1 (8.5°), which is a direct consequence of LP2’s higher ring strain caused by the embedded thiophenes units.29 As shown in Figure 2, which highlights optimized structure of both CLPs, L-P2 structure has a helical pitch of 18.1 Å compared to 3.6 Å for L-P1. This results in a higher hydrodynamic radius and molecular mass distribution for L-P2. 1 H NMR analysis of P1 and L-P1 was conducted in tetrachloroethane-d2 (TCE-d2) at 383 K, and the spectra are shown in Figure 3. P1 presents broadened doublet centered at 7.12 ppm associated with protons Ha and Hb. Two other broad C


Article

Macromolecules

Figure 4. (a) UV−vis spectra of P1, P2, L-P1, and L-P2 in THF solutions and thin films. (b) Emission spectra of L-P1 and L-P2 in THF excited at 315 and 345 nm, respectively.

cm−1 decreases significantly as a considerable number of HCl molecules are eliminated of L-P1 structure (Figure S20). For L-P2, the intensity of the bands associated with C−H stretching mode of aromatic thiophene rings at 3066 and 3019 cm−1 diminishes upon irradiation for the same reasons as for LP1 (Figure S22). Also, the intensity of the bands associated with C−H stretching of alkyl chains at 2920 and 2849 cm−1 remains constant after irradiation, demonstrating their integrity (Figure S22). Although the bands associated with the CC bond vibration of chlorinated aromatics could not be attributed with certainty, the intensity of the bands associated with opla C−H deformation at 797, 830, and 902 cm−1 diminishes significantly (Figure S23). This clearly indicates the loss of chlorine atoms upon cyclo-dehydrochlorination. Optical properties have been characterized by UV−vis and photoluminescence spectroscopy, and the spectra are depicted in Figure 4. L-P1 and L-P2 present absorption between 300 and 500 nm with their respective maximum wavelength located at 317 and 344 nm. The red-shifted absorption of L-P2 (27 nm) compared to L-P1 is attributed to the presence of two electron-donating thiophene units. Optical bandgaps measured at the absorption band onset range from 3.11 eV for L-P1 to 2.83 eV for L-P2. Such high bandgap ladder polymers have also been reported by Fang et al. in their study of ladderized poly-mcarbazoles and by us for helical graphene nanoribbons.17,18 The linkage of the monomers in the meta position likely hinders an optimal conjugation of the π-electrons over the whole structure, resulting in higher bandgap. L-P1 exhibits two vibronic bands centered at 307 and 323 nm while L-P2 exhibits a featureless absorption band. Likewise, only a small red-shift of 6 nm is observed in the absorption spectrum of L-P1 from solution to solid state, as its 3D compact helical structure effectively restrain the aggregation of the polymer chains. Such a phenomenon has also been reported by Bo et al. for spirobridged ladder-type poly(p-phenylenes) whose absorption spectrum remains unchanged from solution to solid state.37 Unlike L-P1, L-P2 undergoes a significant bathochromic shift (38 nm) from solution to solid state. We hypothesize that intermolecular interactions are more likely responsible for this feature as the extended helical pitches of L-P2 allow interdigitation of the polymer backbones, leading to intermolecular π interactions in the solid state. For L-P1, solution and solid-state spectra are similar, indicative of a rigid structure in both states.

singlets can be distinguished at 7.33 and 7.58 ppm, accounting for protons Hc and Hd, respectively. As expected, irradiation of the precursor P1 generally flattens the 1H NMR spectra of LP1, especially the peaks located in the aromatic region due to a more compact and rigid structure.30 Because of the creation of a more delocalized π-conjugated structure, most of the signals are shifted downfield up to 8.56 ppm. Such a result is also observed in the case of similar indeno[1,2,3-cd]fluoranthene where the signal associated with a proton located in a cove region is strongly shifted downfield compared to its uncyclized counterpart.31 This result strongly indicates that the reaction went to near completion. Also, disparity in symmetries and conformations is thought to broaden the signals. For example, this phenomenon is well documented in the case of highly twisted hexabenzotriphenylenes32,33 and fused helicene chains.34 1 H NMR analysis of P2 and L-P2 has also been conducted in TCE-d2 at 383 K (Figure 3). Compared to P1, the P2 1H NMR spectrum is far simpler as only three broad peaks can be found. Upon irradiation, the same trend is observed than for L-P1. The spectrum flattens and stretches downfield as a rigid and more conjugated backbone is obtained. Interestingly, the L-P2 1 H NMR spectrum is even more broadened and flattened than L-P1. As discussed previously, since L-P2 bears five-membered ring thiophene cycles, the whole structure is more rigid than that of L-P1, which diminishes significantly its degree of freedom in solution. Under such circumstances, the 1H NMR signals resolution decreases considerably.30 Again, these results strongly suggest that the CDHC reaction went to near completion and led to the proposed structure. The completeness of the CDHC reactions upon irradiation of P1 can be attested by FTIR (see Figure S18). Indeed, almost complete vanishing of the band at 4054 cm−1, ascribed to the free rotation of phenyl rings, confirms that the CDHC reaction went to near completion since the whole structure is finally fixed.35,36 As expected, the intensity of aromatic C−H stretching triad at 3084, 3048, and 3023 cm−1 diminishes, as fewer aromatic C−H bonds are present in L-P1 (Figure S19). After irradiation, the alkyl chains remain untouched since the intensity of the bands associated with C−H stretching modes of alkyl chains at 2950 and 2918 cm−1 remains essentially the same (Figure S19). Furthermore, the intensity of the bands associated with opla aromatic C−H deformation at 908 and 826 D


Article

Macromolecules

Figure 5. (a) Photoluminescence spectrum of L-P2 in THF at different concentrations and (b) at fixed concentration (1.1 × 10−5 M) in different solvents.

Figure 6. (a) 2D photoluminescence mapping of a dispersion of HiPco CNTs with L-P2 and (b) absorption spectrum of L-P2/HiPco CNTs dispersion in toluene. Dispersion of CNTs/L-P2 (left inset) and the same solution without CNTs (right inset).

In contrast with P1 and P2, L-P1 and L-P2 show strong photoluminescence properties in solution. The PL maxima of L-P1 and L-P2 are centered at 429 and 480 nm with quite large Stokes shifts of 112 and 136 nm, respectively. Interestingly, the photoluminescence spectrum of L-P2 in THF exhibits a large full width at half-maximum (fwhm) value of 180 nm, compared to only 62 nm for L-P1, with a defined vibronic structure with shoulders at 455 and 480 nm. Broad emission bands as observed for L-P2 has already been reported for large planar aggregating polymers exhibiting excimer/exciplex behavior.38 To assess the presence of intermolecular interaction that could promote the formation of excimers, photoluminescence spectra were recorded at different concentrations. As shown in Figure 5a, the shape of the emission band is strongly affected by the concentration as the band associated with the presence of excimer at ca. 480 and 540 nm decreased significantly upon dilution while the intensity of the emission band attributed to the noninteracting polymer chains at 455 nm increased. This observation is in line with intermolecular interactions rather than intramolecular ones. The intermolecular interactions observed for L-P2 compared to L-P1 can be explained by its larger helical pitch, which allows interdigitation of the coils to

overlap each other, enabling excimer formation in solution. This result is in perfect line with the molecular structure obtained by calculations that showed a more open conformation for L-P2 (see Figure 2). Although we do not rule out the effect of temperature and solubility on excimer formation in this study, we focused our work on the effect of solvent viscosity by investigating L-P2’s emission behavior in different solvent systems.39 As depicted in Figure 5b, the emission spectrum of L-P2 is solvent-dependent. Although minimal changes are observed for photoluminescence spectra recorded in THF, toluene and chloroform (similar viscosity), an important contribution of the excimer to the emission spectrum is noticeable in dichloromethane. Indeed, as dichloromethane presents the lowest viscosity, it allows for faster reorganization of the media in the excited states, thus enabling faster excimer formation upon irradiation. On the contrary, a more viscous solvent would stabilize less effectively an excimer being slower to reorganize in solution. Thus, we observe a smaller contribution to the excimer emission in chlorobenzene, which is in line with his intrinsic higher viscosity. E


Article

Macromolecules

hand, both s- and c-SWCNTs can penetrate inside the helical polymer, which would lead to the dispersion of both conducting and semiconducting SWCNTs and explain the present results, as shown in Figure S25b. Further investigations will focus on the synthesis of an electron-rich helical ladder polymer with smaller cavities.

To explore potential applications of helical ladder polymers, we studied their properties as dispersant of single-walled carbon nanotubes (SWCNT). Macromolecular dispersion of SWCNT has proved to be an effective way to sort semiconducting SWCNTs (s-SWCNTs) but still lacks of specificity toward different chiralities. Recently, Loo et al. demonstrated the use of contorted octabenzocircumbiphenyl to separate (10,3)SWCNT from HiPco and CoMoCAT synthesized CNTs.40 The interactions with nonplanar hydrocarbons as well as side chains wrapping of the carbon nanotubes enhance the chances to sort selectively SWCNT. Since helical ladder polymers L-P1 and L-P2 present such a nonplanar/contorted surface, we envisioned that they could play a role in the endeavor of dispersing s-SWCNT as well as sorting s-SWCNT chiralities. Thus, dispersions of HiPco CNTs with L-P1, L-P2, and sodium dodecyl sulfate (SDS, for the sake of comparison) as dispersants were prepared according to a slightly modified procedure developed by Loo et al.40 After dispersion and centrifugation (see Supporting Information), a dispersion of CNTs with L-P2 was obtained (Figure 6b, see insets). As one may expect from the optimized molecular structure, dispersion of CNTs with L-P1 did not afford stable dispersions since CNTs aggregated after 48 h at rest. As stated previously, the structure of L-P1 is rather dense, stiff, and not flexible. Figure 2b clearly demonstrates how L-P1’s helical pitch is tight and cannot allow CNTs to penetrate between each helical pitch. On the other hand, dispersions of HiPco CNTs with L-P2 did afford stable suspensions for months, as the helical pitch of L-P2 is large enough to accommodate CNTs. To further investigate the properties of the dispersion, we performed photoluminescence 2D excitation spectroscopy to assess dispersant specificity over different CNTs chiralities.42 Figure 6a demonstrates that L-P2/HiPco CNTs dispersion contains a higher content of (9,4) and (8,6) s-SWCNTs as their characteristic photoluminescence peaks are more intense than average. Indeed, diameters of (9,4) and (8,6) SWCNTs are expected to be 10.1 and 10.6 Å,42 respectively, which is reasonable to fit in L-P2’s helical pitch of 18.1 Å. UV−vis−NIR absorption spectroscopy has also been conducted on L-P2/CNTs dispersion. Figure 6b shows defined peaks located between 600−900 nm and 900−1600 nm, which are attributed to the presence of s-SWCNTs from S11 and S22 transitions, respectively, for HiPco and CoMoCAT SWCNTs.41,42 Significantly weaker signals can be observed in the 450−650 nm region, recognized as M11 transitions of metallic SWCNTs, although it overlaps slightly with the absorption of L-P2 (onset located at 450 nm). Unfortunately, this analysis is not conclusive enough to doubtlessly confirm whether L-P2 selectively disperses s-SWCNTs or not. Raman spectroscopy is a powerful tool to determine the content of semiconducting and conducting SWCNTs dispersed in solution depending on the excitation wavelength.43 Indeed, both conducting and semiconducting SWCNTs are resonant with an excitation wavelength of 633 nm. Unfortunately, Figure S25a reveals the presence of c-SWCNTs in the blend as signals of conducting SWCNTs are found below 235 nm. The same trend is also observed in SDS/CNTs dispersion, which is not selective to s-SWCNTs. As one may point out, such a result demonstrates that many dispersion mechanisms can be possible with this particular helical ladder polymerthe most obvious being that SWCNTs can be entangled in helical pitches of the polymers. This mechanism should sort specifically s-SWCNTs as it does for other electron-rich systems.44−48 On the other

■

CONCLUSION In summary, we have applied the cyclo-dehydrochlorination (CDHC) reaction for the synthesis of helical CLPs bearing msubstituted terphenyl and electron-rich m-phenylenedithiophene units based on our previous reported procedure. Both 1H NMR and FT-IR showed ladderization to nearcompletion. According to geometrical optimization of the polymers, L-P1 and L-P2 present a helical pitch of 3.61 and 18.1 Å, respectively. Because of its larger helical pitch, L-P2 demonstrated intermolecular interactions, which has been fully characterized by photoluminescence spectroscopy. L-P2 showed characteristic excimer photoluminescence behavior, which is strongly influenced by concentration and solvent viscosity. Moreover, we have demonstrated that L-P2 showed good dispersion properties of HiPco CNTs. A good selectivity over (9,4) and (8,6) s-SWCNTs was observed, although it does not effectively discriminate semiconducting CNTs from metallic CNTs. This can be explained by a nonselective dispersion mechanism in which the inner cavity of L-P2 can host both type of CNTs. Future investigations will focus on the selective dispersions of s-CNTs by eliminating the inner cavity of the CLPs to avoid any parasitizing dispersion mechanisms.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.7b01722. Experimental procedures and characterization data (1H and 13C NMR, HRMS, FTIR) for all new compounds (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (J.-F.M.). ORCID

Jean-François Morin: 0000-0002-9259-9051 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank the CQMF (Centre Québécois sur le Matériaux Fonctionnels) and the CERMA (Centre de Recherche sur les Matériaux Avancés). This research has been supported by NSERC (Natural Sciences and Engineering Research Council of Canada) through a Discovery Grant. Maxime Daigle thanks the FRQ-NT for a PhD scholarship. We thank Alexandre Douaud and Yannick Ledemi from the Centre d’Optique, Photonique et Laser (COPL) of Université Laval for his Raman analysis expertise as well as Alexandre Grégoire for his help in UV−vis analysis of CNTs dispersions. F


Article

Macromolecules

■

(21) Dai, Y.; Katz, T. J. Synthesis of Helical Conjugated Ladder Polymers. J. Org. Chem. 1997, 62, 1274−1285. (22) Iwasaki, T.; Kohinata, Y.; Nishide, H. Poly(thiaheterohelicene): A Stiff Conjugated Helical Polymer Composed of Fused Benzothiophene Rings. Org. Lett. 2005, 7, 755−758. (23) Iwasaki, T.; Katayose, K.; Kohinata, Y.; Nishide, H. A Helical Ladder Polymer: Synthesis and Magnetic Circular Dichroism of Poly[phenylene-4,6-bis(methylsulfonio)-1,3-diyl triflate]. Polym. J. 2005, 37, 592−598. (24) Murata, M.; Sambommatsu, T.; Watanabe, S.; Masuda, Y. An efficient catalyst system for palladium-catalyzed borylation of aryl halides with pinacolborane. Synlett 2006, 2006, 1867−1870. (25) Vollhardt, K.; Shen, H. Remarkable Switch in the Regiochemistry of the Iodination of Anilines by N-Iodosuccinimide: Synthesis of 1,2-Dichloro-3,4-diiodobenzene. Synlett 2012, 2012, 208− 214. (26) Hohl, B.; Bertschi, L.; Zhang, X.; Schlüter, A. D.; Sakamoto, J. Suzuki Polycondensation toward High Molecular Weight Poly(mphenylene)s: Mechanistic Insights and End-Functionalization. Macromolecules 2012, 45, 5418−5426. (27) Walker, S. D.; Barder, T. E.; Martinelli, J. R.; Buchwald, S. L. A Rationally Designed Universal Catalyst for Suzuki−Miyaura Coupling Processes. Angew. Chem., Int. Ed. 2004, 43, 1871−1876. (28) Hecht, S.; Khan, A. Intramolecular Cross-Linking of Helical Folds: An Approach to Organic Nanotubes. Angew. Chem., Int. Ed. 2003, 42, 6021−6024. (29) Ten dihedral angles have been mesured for each CLPs. See the Supporting Information for further details. (30) Bovey, F. A. The high resolution nuclear magnetic resonance spectroscopy of polymers. Polym. Eng. Sci. 1967, 7, 128−136. (31) Amsharov, K. Y.; Merz, P. Intramolecular Aryl−Aryl Coupling of Fluoroarenes through Al2O3-Mediated HF Elimination. J. Org. Chem. 2012, 77, 5445−5448. (32) Peña, D.; Cobas, A.; Pérez, D.; Guitián, E.; Castedo, L. Kinetic Control in the Palladium-Catalyzed Synthesis of C2-Symmetric Hexabenzotriphenylene. A Conformational Study. Org. Lett. 2000, 2, 1629−1632. (33) Pradhan, A.; Dechambenoit, P.; Bock, H.; Durola, F. Highly Twisted Arenes by Scholl Cyclizations with Unexpected Regioselectivity. Angew. Chem., Int. Ed. 2011, 50, 12582−12585. (34) Pradhan, A.; Dechambenoit, P.; Bock, H.; Durola, F. Fused Helicene Chains: Towards Twisted Graphene Nanoribbons. Chem. Eur. J. 2016, 22, 18227−18235. (35) Li, G.; Yoon, K.-Y.; Zhong, X.; Zhu, X.; Dong, G. Efficient Bottom-Up Preparation of Graphene Nanoribbons by Mild Suzuki− Miyaura Polymerization of Simple Triaryl Monomers. Chem. - Eur. J. 2016, 22, 9116−9120. (36) Narita, A.; Verzhbitskiy, I. A.; Frederickx, W.; Mali, K. S.; Jensen, S. A.; Hansen, M. R.; Bonn, M.; De Feyter, S.; Casiraghi, C.; Feng, X.; Mullen, K. Bottom-up synthesis of liquid-phase-processable graphene nanoribbons with near-infrared absorption. ACS Nano 2014, 8, 11622−11630. (37) Wu, Y.; Zhang, J.; Fei, Z.; Bo, Z. Spiro-Bridged Ladder-Type Poly(p-phenylene)s: Towards Structurally Perfect Light-Emitting Materials. J. Am. Chem. Soc. 2008, 130, 7192−7193. (38) Jenekhe, S. A.; Osaheni, J. A. Excimers and Exciplexes of Conjugated Polymers. Science 1994, 265, 765−768. (39) Salom, C.; Semlyen, J. A.; Clarson, S.; Hernandez Fuentes, I.; Macanita, A. L.; Horta, A.; Pierola, I. F. Viscosity dependence of the excimer to monomer fluorescence ratio. Cyclic and linear polysiloxanes. Macromolecules 1991, 24, 6827−6831. (40) Gao, J.; Sengar, N.; Wu, Y.; Jockusch, S.; Nuckolls, C.; Clancy, P.; Loo, Y. L. Contorted Octabenzocircumbiphenyl Sorts Semiconducting Single Walled Carbon Nanotubes with Structural Specificity. Chem. Mater. 2017, 29, 595−604. (41) Bachilo, S. M.; Strano, M. S.; Kittrell, C.; Hauge, R. H.; Smalley, R. E.; Weisman, R. B. Structure-Assigned Optical Spectra of SingleWalled Carbon Nanotubes. Science 2002, 298, 2361−2366.

REFERENCES

(1) Lee, J.; Kalin, A. J.; Yuan, T.; Al-Hashimi, M.; Fang, L. Fully conjugated ladder polymers. Chem. Sci. 2017, 8, 2503−2521. (2) Zou, Y.; Ji, X.; Cai, J.; Yuan, T.; Stanton, D. J.; Lin, Y.-H.; Naraghi, M.; Fang, L. Synthesis and Solution Processing of a Hydrogen-Bonded Ladder Polymer. Chem. 2017, 2, 139−152. (3) Rao, M. R.; Desmecht, A.; Perepichka, D. F. π-Extended Indenofluorenes. Chem. - Eur. J. 2015, 21, 6193−6201. (4) Roncali, J. Synthetic Principles for Bandgap Control in Linear πConjugated Systems. Chem. Rev. 1997, 97, 173−206. (5) Wu, J.-S.; Cheng, S.-W.; Cheng, Y.-J.; Hsu, C.-S. Donor-acceptor conjugated polymers based on multifused ladder-type arenes for organic solar cells. Chem. Soc. Rev. 2015, 44, 1113−1154. (6) Forster, M.; Annan, K. O.; Scherf, U. Conjugated Ladder Polymers Containing Thienylene Units. Macromolecules 1999, 32, 3159−3162. (7) Briseno, A. L.; Kim, F. S.; Babel, A.; Xia, Y.; Jenekhe, S. A. nChannel polymer thin film transistors with long-term air-stability and durability and their use in complementary inverters. J. Mater. Chem. 2011, 21, 16461−16466. (8) Huang, H.; Yang, L.; Facchetti, A.; Marks, T. J. Organic and Polymeric Semiconductors Enhanced by Noncovalent Conformational Locks. Chem. Rev. 2017, 117, 10291−10318. (9) Zhu, C.; Fang, L. Locking the Coplanar Conformation of πConjugated Molecules and Macromolecules Using Dynamic Noncovalent Bonds. Macromol. Rapid Commun. 2017, 1700241. (10) Delnoye, D. A. P.; Sijbesma, R. P.; Vekemans, J. A. J. M.; Meijer, E. W. π-Conjugated Oligomers and Polymers with a Self-Assembled Ladder-like Structure. J. Am. Chem. Soc. 1996, 118, 8717−8718. (11) Guo, X.; Zhou, N.; Lou, S. J.; Hennek, J. W.; Ponce Ortiz, R.; Butler, M. R.; Boudreault, P.-L. T.; Strzalka, J.; Morin, P.-O.; Leclerc, M.; López Navarrete, J. T.; Ratner, M. A.; Chen, L. X.; Chang, R. P. H.; Facchetti, A.; Marks, T. J. Bithiopheneimide−Dithienosilole/ Dithienogermole Copolymers for Efficient Solar Cells: Information from Structure−Property−Device Performance Correlations and Comparison to Thieno[3,4-c]pyrrole-4,6-dione Analogues. J. Am. Chem. Soc. 2012, 134, 18427−18439. (12) Greiner, A. A Commentary on “Polyarylenes and poly(arylenevinylenes), 7. A soluble ladder polymer via bridging of functionalized poly(p-phenylene)-precursors” by U. Scherf, K. Müllen (Makromol. Chem., Rapid Commun. 1991, 12, 489−497). Macromol. Rapid Commun. 2005, 26, 1361−1370. (13) Goldfinger, M. B.; Swager, T. M. Fused Polycyclic Aromatics via Electrophile-Induced Cyclization Reactions: Application to the Synthesis of Graphite Ribbons. J. Am. Chem. Soc. 1994, 116, 7895− 7896. (14) Chmil, K.; Scherf, U. A simple two-step synthesis of a novel, fully aromatic ladder-type polymer. Makromol. Chem., Rapid Commun. 1993, 14, 217−222. (15) Yuan, Z.; Xiao, Y.; Yang, Y.; Xiong, T. Soluble Ladder Conjugated Polymer Composed of Perylenediimides and Thieno[3,2b]thiophene (LCPT): A Highly Efficient Synthesis via Photocyclization with the Sunlight. Macromolecules 2011, 44, 1788−1791. (16) Zhang, C. Y.; Tour, J. M. Synthesis of Highly Functionalized Pyrazines by Ortho-Lithiation Reactions. Pyrazine Ladder Polymers. J. Am. Chem. Soc. 1999, 121, 8783−8790. (17) Lee, J.; Rajeeva, B. B.; Yuan, T.; Guo, Z.-H.; Lin, Y.-H.; AlHashimi, M.; Zheng, Y.; Fang, L. Thermodynamic synthesis of solution processable ladder polymers. Chem. Sci. 2016, 7, 881−889. (18) Daigle, M.; Miao, D.; Lucotti, A.; Tommasini, M.; Morin, J. F. Helically Coiled Graphene Nanoribbons. Angew. Chem., Int. Ed. 2017, 56, 6213−6217. (19) Daigle, M.; Picard-Lafond, A.; Soligo, E.; Morin, J. F. Regioselective Synthesis of Nanographenes by Photochemical Cyclodehydrochlorination. Angew. Chem., Int. Ed. 2016, 55, 2042−7. (20) Dai, Y.; Katz, T. J.; Nichols, D. A. Synthesis of a Helical Conjugated Ladder Polymer. Angew. Chem., Int. Ed. Engl. 1996, 35, 2109−2111. G


Article

Macromolecules (42) Wang, P.-I.; Tsai, C.-Y.; Hsiao, Y.-J.; Jiang, J.-C.; Liaw, D.-J. High-Purity Semiconducting Single-Walled Carbon Nanotubes via Selective Dispersion in Solution Using Fully Conjugated Polytriarylamines. Macromolecules 2016, 49, 8520−8529. (43) Dresselhaus, M. S.; Dresselhaus, G.; Saito, R.; Jorio, A. Raman spectroscopy of carbon nanotubes. Phys. Rep. 2005, 409, 47−99. (44) Liang, S.; Subrahmanyam, A. V.; Khadem, M.; Zhao, Y.; Adronov, A. Selective dispersion of single-walled carbon nanotubes with electron-rich fluorene-based copolymers. RSC Adv. 2016, 6, 25733−25740. (45) Imit, M.; Imin, P.; Adronov, A. Supramolecular interactions of fluorene-based copolymers containing 3,4-propylenedioxythiophene and phenazine units with SWNTs. Polym. Chem. 2016, 7, 5241−5248. (46) Liang, S.; Zhao, Y.; Adronov, A. Selective and Reversible Noncovalent Functionalization of Single-Walled Carbon Nanotubes by a pH-Responsive Vinylogous Tetrathiafulvalene−Fluorene Copolymer. J. Am. Chem. Soc. 2014, 136, 970−977. (47) Wang, H.; Bao, Z. Conjugated polymer sorting of semiconducting carbon nanotubes and their electronic applications. Nano Today 2015, 10, 737−758. (48) Wang, H.; Koleilat, G. I.; Liu, P.; Jiménez-Osés, G.; Lai, Y.-C.; Vosgueritchian, M.; Fang, Y.; Park, S.; Houk, K. N.; Bao, Z. High-Yield Sorting of Small-Diameter Carbon Nanotubes for Solar Cells and Transistors. ACS Nano 2014, 8, 2609−2617.

H


Helical Conjugated Ladder Polymers: Tuning the Conformation and

Recommend Documents