Letter pubs.acs.org/OrgLett
Bay- and Ortho-Octasubstituted Perylenes Youpeng Li,†,∥ Youhua Hong,†,∥ Jing Guo,† Xiaobo Huang,‡ Haipeng Wei,† Jun Zhou,† Tiancheng Qiu,† Jishan Wu,§ and Zebing Zeng*,† †
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, PR China ‡ College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, PR China § Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore S Supporting Information *
ABSTRACT: A key intermediate compound, 2,5,8,11-tetrabromo-1,6,7,12-tetrabutoxyperylene (Per-4Br), was synthesized from 3,6-dibromo-2,7-dioxylnaphthalene via simple regioselective oxidative radical−radical coupling, followed by reduction and nucleophilic substitution. Various bay- and ortho-octasubstituted perylenes containing cyano, methoxy and aryl groups were then obtained by nucleophilic substitution or Pd-catalyzed coupling reactions. X-ray crystallographic analyses reveal that these new perylene molecules process a twisted structure due to steric congestion at the bay-regions and there is no obvious intermolecular π−π interaction. As a result, they exhibit moderate fluorescence quantum yields even in solid state. Therefore, Per-4Br can serve as a versatile building block for various functional perylene dyes with tunable optoelectronic property.
P
2,5,8,11-perylene tetraboronic ester by Ir-catalyzed direct borylation of perylene with B2(pin)2 by taking advantage of the different steric hindrance of the peri-, ortho- and baypostions.12 Poor solubility is another obstacle in the chemical functionalizations as well as their applications.13 Recently, functionalization of PDIs with four methoxy groups was achieved at bay-areas.14 So far, the approach toward functional perylenes at peri- or bay- or ortho-positions commonly relies on the substrate of perylene dianhydride or PDIs. Thus, a rather limited number of perylenes without carboximides has been synthesized so far, especially for the functionalization at the ortho-positions (2,5,8,11-sites).15 To solve the chemical selectivity and solubility problems, and to enrich the perylene family, in this Letter, a 2,5,8,11tetrabromo-1,6,7,12-tetrabutoxyperylene (Per-4Br) was designed and synthesized as a versatile building block of perylene based dyes (Scheme 1). The 3,6-dibromo-2,7 dihydroxynaphthalene 1 was used as a reaction substrate, which is also useful for preparation of other challenging polycyclic aromatic hydrocarbons.16 Intermolecular oxidative coupling of compound 1 gave the dihydroxyperylenequinone as two tautomers (trans-2 and cis-2). A rational mechanism for this intermolecular oxidative cyclodehydrogenation was also proposed (Scheme 1). It involves an initial formation of 3,6dibromonaphthalene-2,7-dioxyl diradical species upon oxidation,17 which is in resonance with several carbon-centered
erylene and its vast amount of derivatives have gained tremendous attention in the field of dye chemistry and materials science.1 The chemical structure of parent perylene can be viewed as two peri-fused naphthalene units,2 in which the inner peri-bond length is unusually longer3 compared to other linearly fused aromatic hydrocarbons such as acenes. In this respect, the π-electrons have partially delocalized over the entire perylene skeleton. Thanks to the rigid framework, perylene captures light strongly in the UV−vis region (λmax = 434 nm),4 and displays intense blue fluorescence in solution. For perylene derivatives, their fluorescence spectra are commonly being a mirror image of absorption, leading to a small Stokes shift.4 However, strong fluorescence cannot be maintained in the concentrated solution or solid state due to aggregation-caused quenching (ACQ). To explore chemical versatility and attractive physical properties of perylene, much attention has been given to its functional derivatives.5 For instance, perylene-3,4,9,10-tetracarboxylic acid diimides (PDIs) were exploited as structural motifs of dyes, pigments,6 semiconductors7 and supramolecular assemblies8 due to the unique π-conjugation structure and optoelectronic properties. Additionally, chromophores derived from perylene exhibit excellent chemical, thermal and photochemical stability.9 Although perylene skeleton was first synthesized by oxidatively fusing two peri-positions of 1,1′-dinaphthyl in 1910,10 it was not until the 1990s that a more applicable preparation method was developed, starting from perylene3,4,9,10-tetracarboxylic dianhydride.11 However, direct functionalization of perylene aromatic core is quite difficult due to the lack of regioselectivity. One rare example is the synthesis of © 2017 American Chemical Society
Received: July 31, 2017 Published: September 13, 2017 5094
DOI: 10.1021/acs.orglett.7b02370 Org. Lett. 2017, 19, 5094−5097
Letter
Organic Letters Scheme 2. Chemical Functionalizations of Per-4Bra
Scheme 1. Synthetic Route of Per-4Br
diradicaloids. The two bromine atoms effectively block the reactive sites at 3- and 6-positions on the naphthalene moiety and suppress possible oligomeric and polymeric side-products. Subsequently, the intermolecular radical−radical coupling reaction18 afforded dimeric product in high yield, followed by simultaneous dehydrogenation. In case of no bromine atom at ortho-position, oligomeric byproduct (i.e., trimer) was found (Figure S1). The possible one-step biradical coupling reaction was also investigated by additional experiments (Figure S2− S4). It turned out that the dimerization worked very well when dilute potassium permanganate solution in methanol and water (v/v = 1:3) was used during the screening of various equivalent oxidant for optimized coupling conditions (Table S1), and compounds trans-2 and cis-2 were obtained in a total yield of 97%. For Compound 2, only 10 resonances were observed in the 13C NMR (see SI), favoring to compound trans-2 due to stabilization of dipole−dipole interactions. Nevertheless, our recent experiments showed trans-to-cis tautomerization was allowed at room temperature in case of reaction with hydrazine hydrate.17 One interpretation is that the dihydroxy compound 2 exists as a mixture of both cis and trans-forms, and that transcompound dominates in the mixture. Both tautomers were mildly reduced into 2,5,8,11-tetrabromo-1,6,7,12-tetrahydroxyperylene 3 by Na2S2O4 (Scheme 1) or possibly oxidized into tetraone by electrochemistry (Figure S5). Without further purification, flexible n-butyl chains were then introduced to the hydroxyl groups at the bay-region by nucleophilic substitution under basic condition, and the desired Per-4Br was obtained in 83% yield. To the best of our knowledge, this is the first time that perylene core possess substitutions not only at baypositions but also with bromo functional groups at orthopositions, favoring postmodication. Per-4Br exhibited good solubility in common organic solvents. Nucleophilic substitution reaction of compound Per-4Br with copper cyanide or sodium methoxide, afforded directly the ortho-functionalized perylenes Per-4CN in 82% yield or Per-4OMe in 80% yield (Scheme 2). Attaching of electron-withdrawing cyano group or electron-donating methoxy group is expected to significantly tune the optoelectronic properties. In addition, the palladium-catalyzed Suzuki coupling of Per-4Br with arylboronic acid (i.e., 4-formyl or 4diphenylamino phenylboronic readily gave the ortho-substituted Per-4CHO/4TPA in high yield (85%). These compounds in solid state showed different colors, from a light yellow to yellowish red (inset in Scheme 1). In some cases, fluorescence color in solid-state are red-shifted relative to that in solution (i.e., Per-4OMe). In addition, Per-4CHO possibly endows as a new soluble and functionalizable building block, for example, for imine-linked covalent organic framework19 based on perylene core.
a
Inset: photos of the each solid sample at room light (left) and images of solid-state emission (right) excited at 365 nm.
The UV−vis absorption spectra of these new perylene dyes were recorded in CH2Cl2 (Figure 1a). Per-4Br showed a well-
Figure 1. (a) UV−vis and (b) normalized emission spectra of the new perylene derivatives in CH2Cl2. Inset: images of solution emission excited at 365 nm.
resolved vibronic structure similar to other perylene dyes, with absorption maximum (λmax) at 443 nm. The λmax (454 nm) of Per-4CN exhibited a red-shift of 1015 cm−1 with respect to that of parent perylene (434 nm),4 likely due to the intramolecular donor−acceptor (D−A) interaction. A similar electronic absorption band structure was observed for compounds Per4CHO and 4TPA, with λmax at 452 and 451 nm, respectively. Compound Per-4OMe displayed a major absorption at 395 nm, with a shoulder at 422 nm, which is blue-shift (2275 cm−1) in comparison with that of parent perylene. Such blue shift can be explained by the twisted structure, which can diminish the πconjugation through the perylene backbone. From the lowestenergy absorption edge, the optical energy gap of Per-4OMe was determined to be 2.8 eV, while relatively smaller gaps of about 2.5−2.6 eV were found for other derivatives (Table S2). All these compounds exhibited one emission band in CH2Cl2 (Figure 1b), with emission maxima (λem) at 489, 514, 500, 474 and 490 nm for Per-4Br, Per-4CN, Per-4CHO, Per-4OMe and Per-4TPA, respectively. The fluorescence quantum yield (Φ) was determined as of 0.30, 0.48, 0.25, 0.63, 0.67, respectively (Table S2). The emission profiles are quite different from that of typical perylenes, which usually resembles the absorption band in a mirror image with a very small Stokes shift. A relatively larger Stokes shift of 2277, 2571, 2124, 2600 5095
DOI: 10.1021/acs.orglett.7b02370 Org. Lett. 2017, 19, 5094−5097
Letter
Organic Letters and 1765 cm−1 was determined for Per-4Br, Per-4CN, Per4CHO, Per-4OMe and Per-4TPA, respectively, presumably due to the twisted backbone and the donor/acceptor substituting effect. Notably, except Per-4CHO (0.03), moderate solid-state photoluminescence quantum yields were measured for others (0.10, 0.21, 0.13 and 0.11 for Per-4Br, Per-4CN, Per-4OMe and Per-4TPA, respectively), and their photoluminescence color ranged from yellow to green (inset in Scheme 2). This feature appears to be an attractive characteristic of these perylene series since most perylene dyes tend to quench fluorescence in solid state. To elucidate the influence of the ortho-substituents on the energy levels of the molecular orbitals, the electrochemical properties of the new perylenes were investigated by cyclic voltammetry (CV) (Figure 2 and Table S2). Compounds Per-
Figure 3. ORTEP drawing of (a) Per-4CN, (b) Per-4CHO and (c) Per-4OMe with selected bond lengths (in Å), hydrogen atoms are omitted for clarity; (d) packing structures of Per-4CN. Thermal ellipsoids are shown at 50% probability; hydrogen atoms are omitted for clarity.
bay substituents.20 The random conformation with diminishing dihedral angle possibly exists and resembles a transition state, which may be stabilized by the short contacts (i.e, C···O···H interactions in the eight alkoxyl groups functionalizd Per4OMe). Such feature is likely responsible for red-shift fluorescence in the solid state relative to solution. However, the dynamic equilibria are not easy to be observed in the crystal state. To understand the electronic structure and the observed physical properties, density functional theory (DFT) calculations were carried out at B3LYP/6-31G (d, p) level. The optimized geometries are consistent with their single crystallographic structures (Figure S11). As shown in Figure 4, both the HOMO and LUMO were mainly delocalized over the perylene backbone, with some coefficients at the OR (HOMO) or CN/ −CHO (LUMO) groups. The calculated HOMO energy levels showed similar energy trends to the experimental date. TDDFT calculations (at B3LYP/6-311G (d, p) level) were also performed (Figure S12−S21 and Table S3−S7). In all cases,
Figure 2. Cyclic voltammograms of the new perylene dyes in CH2Cl2 (10−3 mol L−1); scan rate 100 mVs−1, vs Fc/Fc+.
4Br, Per-4CHO, Per-4OMe and Per-4TPA all displayed two reversible oxidation waves, indicative of stepwise formation of radical cations and dications upon electrochemical oxidation. The perylenes substituted with donors at ortho-positions such as Per-4OMe and Per-4TPA exhibited significantly lowered first oxidative potentials and higher lying HOMO energy levels. On the other hand, compound Per-4CN showed one irreversible oxidative wave and one reduction wave with the onset potential at 0.69 V and −1.63 V (vs Fc/Fc+), respectively. Both HOMO and LUMO are decreased due to the strong electron-withdrawing effect of the cyano groups. Single crystals of Per-4CN, Per-4CHO and Per-4OMe suitable for X-ray crystallographic analysis were obtained by slow diffusion of hexane to their chloroform solutions. As illustrated in Figure 3, in all cases, the perylene skeletons are highly twisted out of planarity due to the steric congestion at the bay-regions (Figure S6−S10). The average dihedral angle of the two naphthalene rings at the bay-area was determined as about 30.99°, 32.25° and 32.08° for Per-4CN, Per-4CHO and Per-4OMe, respectively. The average length of the C−C bonds linking the two naphthalene units was found as about 1.46− 1.47 Å, comparable to that of typical perylene (1.47 Å).3 Both the P-enantiomer and M-enantiomer were present in the unit cell, and besides some intramolecular [CH···NC] (e.g., in Per4CN) or [CH···π] and [CH···O] short contacts, there is no π−π interaction. Such packing structure well explains the observed moderate photoluminescence in solid state. The twist scaffold induces molecular flexibility, while the activation barrier for interconversion of (P)- and (M)-enantiomers depends on
Figure 4. Calculated molecular orbital profiles and energy diagrams of the HOMOs and LUMOs of the new perylenes. 5096
DOI: 10.1021/acs.orglett.7b02370 Org. Lett. 2017, 19, 5094−5097
Letter
Organic Letters the lowest-energy absorption band is correlated to HOMO → LUMO electronic transition, while its higher energy shoulder can be assigned to HOMO−1 → LUMO and HOMO → LUMO+1 transitions. It is worth noting that the substituents at ortho position affect the higher energy transitions. For example, a coefficient separation between HOMO−1 and LUMO was observed in Per-4TPA, indicative of a charge-transfer band for this compound. The differences on substituent’s contribution to the higher energy transitions would be attributable to the minor variations in absorption of these perylenes. In summary, we have developed a facile synthetic approach to make a 2,5,8,11-tetrabromo-substituted perylene building block, which allows various functionalization at the orthopositions via either nucleophilic substitution or Pd-catalyzed coupling reaction. The new ortho- and bay-octasubstituted perylenes have highly twisted structure and nicely suppress the intermolecular π−π interactions. As a result, they are all highly soluble and show moderate fluorescence quantum yield even in the solid state. They exhibit tunable electronic and optical properties with large Stokes shift, and thus have potential applications as organic optoelectronic materials.21 In addition, Per-4Br and Per-4CHO possibly can be used as new structural motifs for the construction of organic dyes based 2D and 3D covalent organic frameworks in future.
■
(4) Berlman, I. B. Handbook of Fluorescence spectra of Aromatic Molecules; Academic Press: New York, 1971. (5) Markiewicz, J. T.; Wudl, F. ACS Appl. Mater. Interfaces 2015, 7, 28063. (6) (a) Nagao, Y. Prog. Org. Coat. 1997, 31, 43. (b) Chen, L.; Li, C.; Müllen, K. J. Mater. Chem. C 2014, 2, 1938. (7) (a) Jones, B. A.; Ahrens, M. J.; Yoon, M. H.; Facchetti, A.; Marks, T. J.; Wasielewski, M. R. Angew. Chem., Int. Ed. 2004, 43, 6363. (b) Zhan, X.; Facchetti, A.; Barlow, S.; Marks, T. J.; Ratner, M. A.; Wasielewski, M. R.; Marder, S. R. Adv. Mater. 2011, 23, 268. (c) Jiang, W.; Li, Y.; Wang, Z. Acc. Chem. Res. 2014, 47, 3135. (8) Würthner, F.; Saha-Mö ller, C. R.; Fimmel, B.; Ogi, S.; Leowanawat, P.; Schmidt, D. Chem. Rev. 2016, 116, 962. (9) (a) Yuan, Z.; Xiao, Y.; Qian, X. Chem. Commun. 2010, 46, 2772. (b) Yan, Q.; Zhou, Y.; Zheng, Y.; Pei, J.; Zhao, D. Chem. Sci. 2013, 4, 4389. (10) Scholl, R.; Seer, C.; Weitzenböck, R. Ber. Dtsch. Chem. Ges. 1910, 43, 2202. (11) van Dijk, J. T. M.; Hartwijk, A.; Bleeker, A. C.; Lugtenburg, J.; Cornelisse, J. J. Org. Chem. 1996, 61, 331. (12) Coventry, D. N.; Batsanov, A. S.; Goeta, A. E.; Howard, J. A.; Marder, T. B.; Perutz, R. N. Chem. Commun. 2005, 36, 2172. (13) (a) Avlasevich, Y.; Li, C.; Müllen, K. J. Mater. Chem. 2010, 20, 3814. (b) Jiménez, Á . J.; Lin, M. J.; Burschka, C.; Becker, J.; Settels, V.; Engels, B.; Würthner, F. Chem. Sci. 2014, 5, 608. (c) Robb, M. J.; Newton, B.; Fors, B. P.; Hawker, C. J. J. Org. Chem. 2014, 79, 6360. (14) Leowanawat, P.; Nowakkról, A.; Würthner, F. Org. Chem. Front. 2016, 3, 537. (15) Zagranyarski, Y.; Chen, L.; Jänsch, D.; Gessner, T.; Li, C.; Müllen, K. Org. Lett. 2014, 16, 2814. (16) (a) Kitamura, C.; Abe, Y.; Ohara, T.; Yoneda, A.; Kawase, T.; Kobayashi, T.; Naito, H.; Komatsu, T. Chem. - Eur. J. 2010, 16, 890. (b) Miyoshi, H.; Miki, M.; Hirano, S.; Shimizu, A.; Kishi, R.; Fukuda, K.; Shiomi, D.; Sato, K.; Takui, T.; Hisaki, I. J. Org. Chem. 2017, 82, 1380. (17) Wei, H.; Qiu, T.; Huang, X.; Zhou, J.; Guo, J.; Jiang, C.; Luo, S.; Zeng, Z.; Wu, J. Chem. Commun. 2017, 53, 6740. (18) Qiu, S.; Zhang, Y.; Huang, X.; Bao, L.; Hong, Y.; Zeng, Z.; Wu, J. Org. Lett. 2016, 18, 6018. (19) Selected examples: (a) Rabbani, M. G.; Sekizkardes, A. K.; Kahveci, Z.; Reich, T. E.; Ding, R.; El-Kaderi, H. M. Chem. - Eur. J. 2013, 19, 3324. (b) Huang, N.; Krishna, R.; Jiang, D. J. Am. Chem. Soc. 2015, 137, 7079. (c) Waller, P. J.; Lyle, S. J.; Osborn Popp, T. M.; Diercks, C. S.; Reimer, J. A.; Yaghi, O. M. J. Am. Chem. Soc. 2016, 138, 15519. (d) Zeng, Y.; Zou, R.; Zhao, Y. Adv. Mater. 2016, 28, 2855. (20) (a) Osswald, P.; Würthner, F. J. Am. Chem. Soc. 2007, 129, 14319. (b) Nowakkrol, A.; Röhr, M.; Schmidt, D.; Würthner, F. Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201705445. (21) (a) Yu, Y.-Q.; Zhang, H.-Y.; Chai, Y.-Q.; Yuan, R.; Zhuo, Y. Biosens. Bioelectron. 2016, 85, 8. (b) Liu, Y.; Gao, X.; Lu, F.; Hu, M.; Shi, L.; Zheng, L. Soft Matter 2017, 13, 3072.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.7b02370. Experimental details, single-crystal X-ray diffraction data, NMR spectra and calculations (PDF) X-ray crystallographic data for Per-4CN (CIF) X-ray crystallographic data for Per-4CHO (CIF) X-ray crystallographic data for Per-4OMe (CIF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Jishan Wu: 0000-0002-8231-0437 Zebing Zeng: 0000-0002-6246-3911 Author Contributions ∥
Y.L. and Y.H. contributed equally to this work.
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We thank the National Natural Science Foundation of China (21502049 and 51573040), start-up funding of Hunan University (531109020043) and the Singapore MOE Tier 3 programme (MOE2014-T3-1-004) for financial support.
■
REFERENCES
(1) (a) Wu, J.; Pisula, W.; Müllen, K. Chem. Rev. 2007, 107, 718. (b) Zaumseil, J.; Sirringhaus, H. Chem. Rev. 2007, 107, 1296. (2) Viruela-Martin, R.; Viruela-Martin, P. M.; Orti, E. J. Chem. Phys. 1992, 97, 8470. (3) Morgan, G. T.; Mitchell, J. G. J. Chem. Soc. 1934, 536. 5097
DOI: 10.1021/acs.orglett.7b02370 Org. Lett. 2017, 19, 5094−5097
