Letter Cite This: Org. Lett. 2018, 20, 6117−6120
pubs.acs.org/OrgLett
Selective Ortho-π-Extension of Perylene Diimides for Rylene Dyes Jiajun Wu,† Dezhi He,† Yujiao Wang,‡ Feng Su,† Zongxia Guo,‡ Jianbin Lin,† and Hui-Jun Zhang*,† †
Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People’s Republic of China ‡ School of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China
Org. Lett. 2018.20:6117-6120. Downloaded from pubs.acs.org by UNIV OF SUNDERLAND on 10/05/18. For personal use only.
S Supporting Information *
ABSTRACT: A range of ortho-π-extended PDI derivatives are straightforwardly synthesized in good yields through highly regioselective heteroannulations of ortho-alkynylsubstituted PDI derivatives with sulfur, selenium, or nitrogen nucleophiles. Successful synthesis of pyrrole-fused rylene dyes by using primary amines as nucleophiles indicates the great synthetic potential of this facile annulation route. Further opto-electrochemical study of these novel thiophene-, selenophene-, and pyrrole-fused PDIs suggests that effective π-conjugation enlargement combined with distortion of the perylene core renders these PDI derivatives tunable and desirable physical properties.
A
perylene dyes are greatly enhanced due to their structural planarity, which can lead to much lower solubilities and increased charge recombination as well as excimer formation. Incorporating a twisting structure represents a useful strategy to disrupt π−π interactions.8 As of now, there are only a few reports concerning π-expanded perylene dyes with unusual conformations due to the synthetic challenge.9 Like π-fusion of naphthalene diimides (NDIs) with (hetero)arenes (Scheme 1b) which affords remarkable bathochromically shifted absorptions as well as higher stabilities and solubilities,10 lateral ortho-π-extension of PDIs with (hetero)aromatic rings (Scheme 1c) may not only increase the number of aromatic sextets on their electronic structures but also lead to more stable and diversified rylene derivatives. Moreover, repulsive interactions between the sterically encumbered bay-substituents may lead to twisted conformations of the π-systems. More importantly, the number, position, and valence state of different heteroatoms within the π-skeleton of ortho-π-extended PDIs may also have significant influence on their optical and electrochemical properties. Recently, we have reported a Rh(III)-catalyzed highly regioselective direct ortho-iodination of PDIs,11 which can provide key intermediates for the preparation of various ortho-functionalized PDIs including ortho-alkynyl substituted PDIs. Herein, we present our further efforts on the design and synthesis of a range of thiophene-, selenophene-, and pyrrolefused PDIs through highly regioselective and convenient annulations of the alkynyl substituted PDIs with different nucleophiles.
s key building blocks for achieving novel organic semiconductors with exciting performance, perylene diimides (PDIs) have received considerable research interest from both academia and industry.1 Significant efforts were devoted to the development of new powerful synthetic strategies toward diversified PDI derivatives.2 Conjugation enlargement of perylene cores is a promising approach to achieve higher rylene chromophores with superior properties such as narrow HOMO−LUMO gaps, long-wavelength absorptions/emissions, lower oxidation/reduction potentials, and enhanced electron transfer abilities.3 However, the syntheses of π-extended PDI skeletons, especially the longitudinal extended ones, are very cumbersome and challenging.4 Recently, a number of laterally π-extended perylene dyes, such as coronene diimides,5 dibenzocoronene diimides,6 and their heterocyclic analogues,7 were readily synthesized. However, a common feature of their structures is π-extension in the bay-region of PDI cores (Scheme 1a), which normally results in hypsochromically shifted absorptions. In addition, the π-stacking and crystallinities of most π-extended Scheme 1. Core-Expanded Rylene Diimides
Received: August 9, 2018 Published: September 25, 2018 © 2018 American Chemical Society
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DOI: 10.1021/acs.orglett.8b02557 Org. Lett. 2018, 20, 6117−6120
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Organic Letters
of trimethylsilylethynyl-substituted PDI 2b′ with different sulfur reagents were also conducted. With the addition of S8 as a sulfur source, both trimethylsilyl-substituted product 3b′ and the corresponding desilylation product 3b were formed as a mixture. The vacant thiophene α-position in 3b is important for further modifications. Notably, the reaction of 2b′ with 3 equiv of Na2S·9H2O led to the selective formation of 3b in 85% yield (entry 6). Ethynyl-substituted PDI 2b also reacted with Na2S·9H2O affording 3b in relatively lower yield (58%, entry 7). Subsequently, the annulation of much less reactive 2c with K2S was performed, which also produced 3c in moderate yield (58%, entry 8). Compared with the sulfur atom, the selenium atom has a bigger and looser outermost electron cloud that is advantageous for better orbital overlap and charge transport.14 Therefore, the reaction of 2a with 4 equiv of Se powder was conducted, which led to the formation of corresponding selenophene-fused PDI 3d in 62% yield (entry 9). Having these interesting results in hand, we then investigated the thienannulations of tetra-alkynyl-substituted PDIs 4 with S8 and K2S, respectively (Scheme 2). For
Because the high polarizability of sulfur atoms gives rise to strong S···S and S···π intermolecular interactions which may contribute to high charge mobilities,12 thiophene-fused NDIs such as naphtho[2,3-b:6,7-b′]dithiophene diimide (NDTI) and naphtho[2,3-b]thiophene diimide (NTI) were developed by Takimiya et al. as efficient building blocks for n-type and ambipolar organic semiconductors. Recently, Itami et al. reported a simple but efficient method for the synthesis of thiophene-fused π-systems via a thienannulation of arylethynylsubstituted polycyclic arenes with elemental sulfur (S8).13 In this context, we envisioned selective construction of thiophenefused PDIs through the thienannulation of ortho-alkynylsubstituted PDIs. Initially, three monoalkynyl-substituted PDIs 2a, 2b′, and 2c were prepared in high yields through Pd-catalyzed Sonogashira couplings of ortho-iodinated PDI 1 with three terminal alkynes (Table 1; for details, see the Supporting Information). Table 1. Heteroannulation of 2a−c and 2b′ with Different Sulfur and Selenium Reagentsa
Scheme 2. Synthesis of Tetrathiophene-Fused PDI 5
entry
PDI (mmol)
[Nu] (equiv)
t (°C)
3, yield (%)b
c
2a (0.1) 2a (0.05) 2a (0.1) 2a (0.05) 2a (0.1) 2b′ (0.05) 2b (0.05) 2c (0.05) 2a (0.05)
S8 (1) K2S (3) Na2S·9H2O (3) KSAc (3) KSAc (3) Na2S·9H2O (3) Na2S·9H2O (3) K2S (3) Se (4)
140 80 80 80 140 80 80 80 140
3a, 77 3a, 70 3a, 63 3a, 54 3a, 69 3b, 85 3b, 58 3c, 58 3d, 62
1 2 3 4d 5 6d 7d 8 9c,e
phenylethynyl substituted 4a, addition of S8 or K2S as the sulfur source resulted in the formation of tetrathiophene-fused PDI 5a in 85% or 45% yield. However, the thienannulation of 1-hexynyl substituted 4b proceeded smoothly only in the presence of K2S and afforded the desired product 5b in 20% yield. Compared to thiophene-fused rylenes, pyrrole-fused analogues have rarely been reported partly due to the lack of effective routes toward these compounds.15 Motivated by the facile synthesis of thiophene-fused PDIs through annulations of ortho-alkynyl substituted PDIs with nucleophilic sulfur reagents, we expected to construct similar pyrrole-fused rylenes via the annulation of 2 with primary amines. After a very careful screening of reaction conditions, we found that performing the reaction of 2a with BnNH2 and BuNH2, respectively, in the presence of tBuOK could lead to the formation of desired products 6a and 6b in good yields (Scheme 3). It is noteworthy that treatment of 2a with BnNH2 in the absence of tBuOK only afforded a formal hydration product 6′, which indicated the attack of nitrogen on the alkyne group followed by the formation of an imine intermediate during the reaction.16 Perhaps due to the strong steric repulsions between neighboring N-substituents, our attempt to prepare the corresponding tetrapyrrole-fused PDIs has failed. Based on these experimental results and literature precedents,17 we depict a plausible mechanism for the present transformations (see Scheme S1). Regioselective [1,6]-
a
Reaction conditions: 2, chalcogen sources (S8, K2S, Na2S·9H2O, KSAc, and Se powder), solvent (DMF, 0.5 mL for 0.05 mmol scale reaction; 1.0 mL for 0.1 mmol scale reaction) at 80 or 140 °C under Ar for 20 h. bIsolated yield of 3. cDMAC as solvent. d12 h. eReact for 36 h.
Treatment of 2b′ with K2CO3 in MeOH/CHCl3 provided the corresponding ortho-ethynyl-substituted PDI 2b in 99% yield. Then the reactions of 2a−c and 2b′ with different sulfur reagents were investigated (Table 1). Interestingly, although the electron-deficient PDI 2a is actually not an ideal substrate for an electrophilic thienannulation process,13 treatment of 2a with 1.0 equiv of S8 at 140 °C indeed afforded the desired product 3a in 77% yield (entry 1). Moreover, the annulation of 2a with potassium sulfide (K2S) or sodium sulfide (Na2S· 9H2O) instead of S8 proceeded smoothly even at 80 °C and produced 3a in good yields (entries 2 and 3). Potassium thioacetate (KSAc) was also effective for this thienannulation reaction (entries 4 and 5). The annulation of 2a with KSAc at 140 °C afforded 3a in 69% yield (entry 5). Then the reactions 6118
DOI: 10.1021/acs.orglett.8b02557 Org. Lett. 2018, 20, 6117−6120
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Organic Letters Scheme 3. Synthesis of Pyrrole-Fused PDI 6
Figure 2. HPLC traces of compound 5a on a Daicel Corporation IE Chiral Column at ambient conditions using n-hexane/chloroform (13:7) as eluent.
conjugate additions of sulfur, selenium, or nitrogen nucleophiles on the alkynyl substituent of PDIs may initiate the heteroannulations. This is different from the mechanism proposed by Itami et al. for the thienannulation of diarylacetylenes,13 because an electrophilic attack of S8 on the electron-deficient 2a would be rather difficult. All these ortho-π-extended PDIs showed enhanced solubility in common organic solvents, such as dichloromethane, chloroform, and tetrahydrofuran. The optophysical properties of compounds 3a−d, 5a, and 6a−b were studied by UV− visible spectroscopy. Compared to PDI-ref, substantial red shifts in the spectra of 3a−d indicated effective expansion of the π systems even through the fusion with only one thiophene or selenophene ring (Figure 1a−c). Substituents on the
Thereafter, electronic structures of these ortho-π-extended PDIs were also evaluated (Table 2, Figure S1). Compared to Table 2. Summary of Electrochemical Properties of PDIs PDIs
Ered1 [V]a
Ered2 [V]a
Eg [eV]b
LUMO [eV]c
HOMO [eV]d
PDI-ref 3a 3b 3c 3d 5a 6a 6b
−1.16 −1.04 −1.04 −1.07 −1.04 −0.89 −1.14 −1.15
−1.33 −1.25 −1.25 −1.26 −1.24 −1.03 −1.34 −1.37
2.29 1.92 1.91 1.90 1.94 1.55 1.82 1.80
−3.67 −3.76 −3.76 −3.73 −3.76 −3.91 −3.66 −3.65
−5.96 −5.68 −5.67 −5.63 −5.70 −5.46 −5.48 −5.45
a
Estimated from onset potentials, determined by cyclic voltammetric measurement in 0.1 M solution of Bu4NPF6 in DCM: vs Fc/Fc+. bEg = optical gap, calculated from the optical absorption data. cEstimated vs vacuum level from LUMO = 4.80 eV − Ered1. dEstimated from HOMO = LUMO − Eg.
the parent unsubstituted PDI-ref, they all possess much lower HOMO−LUMO gaps. The ring fusion of PDI with thiophene and selenophene can both lower the LUMO levels and increase the HOMO levels. Tetrathiophene-fused PDI 5a exhibited the lowest HOMO−LUMO gap. The ring fusion of PDI with more electron-rich pyrrole endowed 6a and 6b with both raised HOMO and LUMO values. The extent of raising the HOMO is much larger than raising the LUMO, which has also been observed for the core-extended NDIs.3c All these results suggest that not only the electrochemical properties but also the conformations of ortho-π-extended PDIs can be tailored by the extent of π-conjugation and the nature of different heteroatoms within the π-skeleton. To gain better insight into the molecular orbitals of these fused PDIs, the structures and frontier molecular orbital profiles of 3a, 3d, and 6b were optimized by density functional theory (DFT) calculations at the B3LYP/6-31G(d) level in the Gaussian 09 suite of programs. According to the optimized structures (Figure 3), the C13C14C1X (X = S in 3a, Se in 3d, and N in 6b) dihedral angles are 8.2°, 10.0°, and 14.5°, respectively. The frontier molecular orbital profiles shown in Figure 3 also indicate that the LUMO of these fused PDI tends to localize on the perylene core, whereas the HOMO tends to delocalize in the lateral direction. This implies that ortho-πextension of PDIs can provide a good opportunity to finely affect the HOMO but keep the LUMO almost intact. In conclusion, the facile and selective annulation of orthoalkynyl-substituted PDI derivatives with sulfur, selenium, or
Figure 1. UV−visible absorption spectra of (a) PDI-ref, (b) 3a−c, (c) 3d, (d) 5a, and (e) 6a−b in chloroform (10 μM).
thiophene ring only displayed slight influence on the optical absorption properties of 3a−c (Figure 1b). This is different from the remarkable substituent effects observed for thiophene-fused NDI skeletons.18 Moreover, the spectra of 3a−d showed well-resolved vibronic structures (0−0, 0−1, and 0−2 transitions, Figure 1b,c), which implied their almost planar and rigid conformations. In contrast, the spectra of 5a and 6a−b exhibited broadened absorption bands and partially resolved vibrational progression (Figure 1d,e), which indicated their twisted structures originated from the steric repulsion between bay-substituents. Chiral HPLC analysis of 5a also suggested the significant distortion of the perylene core (Figure 2).19 In addition, introduction of four thiophene rings induced a substantial bathochromic shift in the absorption spectrum of 5a due to the largely extended πconjugation (Figure 1d). Compounds 6a and 6b that were fused with more electron-rich pyrrole rings displayed ∼30 nm red shifts compared to the thiophene-fused PDI 3a (Figure 1e). 6119
DOI: 10.1021/acs.orglett.8b02557 Org. Lett. 2018, 20, 6117−6120
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Int. Ed. 2017, 56, 11144−11164. (c) Takimiya, K.; Nakano, M. Bull. Chem. Soc. Jpn. 2018, 91, 121−140. (d) Zhylitskaya, H.; Stępień, M. Org. Chem. Front. 2018, 5, 2395−2414. (4) Chen, L.; Li, C.; Mullen, K. J. Mater. Chem. C 2014, 2, 1938− 1956. (5) Rohr, U.; Schlichting, P.; Böhm, A.; Gross, M.; Meerholz, K.; Bräuchle, C.; Müllen, K. Angew. Chem., Int. Ed. 1998, 37, 1434−1437. (6) Muller, S.; Mullen, K. Chem. Commun. 2005, 4045−4046. (7) (a) Langhals, H.; Kirner, S. Eur. J. Org. Chem. 2000, 2000, 365− 380. (b) Qian, H.; Liu, C.; Wang, Z.; Zhu, D. Chem. Commun. 2006, 4587−4589. (8) (a) Jiang, W.; Li, Y.; Wang, Z. Acc. Chem. Res. 2014, 47, 3135− 3147. (b) Jiang, W.; Ye, L.; Li, X.; Xiao, C.; Tan, F.; Zhao, W.; Hou, J.; Wang, Z. Chem. Commun. 2014, 50, 1024−1026. (c) Zhong, Y.; Trinh, M. T.; Chen, R.; Purdum, G. E.; Khlyabich, P. P.; Sezen, M.; Oh, S.; Zhu, H.; Fowler, B.; Zhang, B.; Wang, W.; Nam, C.-Y.; Sfeir, M. Y.; Black, C. T.; Steigerwald, M. L.; Loo, Y.-L.; Ng, F.; Zhu, X. Y.; Nuckolls, C. Nat. Commun. 2015, 6, 8242. (d) Hartnett, P. E.; Matte, H. S. S. R.; Eastham, N. D.; Jackson, N. E.; Wu, Y.; Chen, L. X.; Ratner, M. A.; Chang, R. P. H.; Hersam, M. C.; Wasielewski, M. R.; Marks, T. J. Chem. Sci. 2016, 7, 3543−3555. (9) (a) Désilets, D.; Kazmaier, P. M.; Burt, R. A.; Hamer, G. K. Can. J. Chem. 1995, 73, 325−335. (b) Avlasevich, Y.; Müller, S.; Erk, P.; Müllen, K. Chem. - Eur. J. 2007, 13, 6555−6561. (c) Yao, J. H.; Chi, C.; Wu, J.; Loh, K.-P. Chem. - Eur. J. 2009, 15, 9299−9302. (d) Yue, W.; Jiang, W.; Böckmann, M.; Doltsinis, N. L.; Wang, Z. Chem. - Eur. J. 2014, 20, 5209−5213. (e) Chaolumen; Enno, H.; Murata, M.; Wakamiya, A.; Murata, Y. Chem. - Asian J. 2014, 9, 3136−3140. (f) Regar, R.; Mishra, R.; Mondal, P. K.; Sankar, J. J. Org. Chem. 2018, 83, 9547−9552. (g) Zeng, C.; Xiao, C.; Feng, X.; Zhang, L.; Jiang, W.; Wang, Z. Angew. Chem., Int. Ed. 2018, 57, 10933−10937. (10) (a) Fukutomi, Y.; Nakano, M.; Hu, J.-Y.; Osaka, I.; Takimiya, K. J. Am. Chem. Soc. 2013, 135, 11445−11448. (b) Osaka, I.; Shinamura, S.; Abe, T.; Takimiya, K. J. Mater. Chem. C 2013, 1, 1297−1304. (c) Yue, W.; Gao, J.; Li, Y.; Jiang, W.; Di Motta, S.; Negri, F.; Wang, Z. J. Am. Chem. Soc. 2011, 133, 18054−18057. (d) Li, C.; Lin, Z.; Li, Y.; Wang, Z. Chem. Rec. 2016, 16, 873−885. (e) Fan, W.; Liu, C.; Li, Y.; Wang, Z. Chem. Commun. 2017, 53, 188− 191. (11) (a) Zhang, L.; He, D.; Liu, Y.; Wang, K.; Guo, Z.; Lin, J.; Zhang, H.-J. Org. Lett. 2016, 18, 5908−5911. (b) Wu, J.; He, D.; Zhang, L.; Liu, Y.; Mo, X.; Lin, J.; Zhang, H.-J. Org. Lett. 2017, 19, 5438−5441. (12) Cinar, M. E.; Ozturk, T. Chem. Rev. 2015, 115, 3036−3140. (13) Meng, L.; Fujikawa, T.; Kuwayama, M.; Segawa, Y.; Itami, K. J. Am. Chem. Soc. 2016, 138, 10351−5. (14) Meng, D.; Sun, D.; Zhong, C.; Liu, T.; Fan, B.; Huo, L.; Li, Y.; Jiang, W.; Choi, H.; Kim, T.; Kim, J. Y.; Sun, Y.; Wang, Z.; Heeger, A. J. J. Am. Chem. Soc. 2016, 138, 375−380. (15) (a) Suraru, S.-L.; Zschieschang, U.; Klauk, H.; Würthner, F. Chem. Commun. 2011, 47, 11504−11506. (b) Qiu, L.; Yu, C.; Zhao, N.; Chen, W.; Guo, Y.; Wan, X.; Yang, R.; Liu, Y. Chem. Commun. 2012, 48, 12225−12227. (16) The ketone product 6′ may be derived from the hydrolysis of an imine intermediate (see the Supporting Information). (17) Mishra, R.; Panini, P.; Sankar, J. Org. Lett. 2014, 16, 3994−7. (18) Nakano, M.; Osaka, I.; Hashizume, D.; Takimiya, K. Chem. Mater. 2015, 27, 6418−6425. (19) (a) Osswald, P.; Reichert, M.; Bringmann, G.; Würthner, F. J. Org. Chem. 2007, 72, 3403−3411. (b) Osswald, P.; Würthner, F. J. Am. Chem. Soc. 2007, 129, 14319−143.
Figure 3. Optimized structures and frontier molecular orbital profiles of molecules based on DFT (B3LYP/6-31G(d)) calculations: (a) optimized structures, (b) HOMO, and (c) LUMO.
nitrogen nucleophiles provides an efficient pathway toward thiophene-, selenophene-, or pyrrole-fused PDIs. The unique and versatile physical properties of these novel ortho-πextended PDIs demonstrated the significance of this annulation strategy as well as our previous work on Rh(III)catalyzed direct ortho-iodination of PDIs. Further development and applications of the ortho-π-extended PDI derivatives are currently underway in our group.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.8b02557. Experimental procedures, full characterization data (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Jianbin Lin: 0000-0002-0064-3079 Hui-Jun Zhang: 0000-0001-9567-3010 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We are grateful for financial support from the Natural Science Foundation of China (Nos. 21572188, 21772162, 21772165), the Fundamental Research Funds for the Central Universities (Nos. 20720160049, 20720180031), and the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (21521004).
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REFERENCES
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DOI: 10.1021/acs.orglett.8b02557 Org. Lett. 2018, 20, 6117−6120
