Subscriber access provided by UCL Library Services Article Doubly Encapsulated Perylene Diimides: Effect of Molecular Encapsulation on Photophysical Properties. Jeroen Royakkers, Alessandro Minotto, Daniel G. Congrave, Weixuan Zeng, Adil Patel, Andrew D. Bond, Dejan-Krešimir Bu#ar, Franco Cacialli, and Hugo Bronstein J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b02597 • Publication Date (Web): 04 Nov 2019 Downloaded from pubs.acs.org on November 19, 2019 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. 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ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts. is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties. Page 1 of 9 The Journal of Organic Chemistry 1 2 3 4 5 6 7 Doubly Encapsulated Perylene Diimides: Effect of Molecular Encap- 8 sulation on Photophysical Properties. 9 10 Jeroen Royakkers†, Alessandro Minotto‡, Daniel G. Congrave†, Weixuan Zeng†, Adil Patel‡, Andrew D. Bond†, Dejan-Krešimir 11 Bučar§, Franco Cacialli‡, Hugo Bronstein†Δ* 12 † 13 Department of Chemistry University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom. ΔCavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom. 14 ‡ 15 Department of Physics and Astronomy and LCN, University College London, Gower Street, London WC1E 6BT, United Kingdom. §Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom. 16 17 18 ABSTRACT: Intermolecular interactions play a fundamental role on the performance of conjugated materials in organic electronic 19 devices, as they heavily influence their optoelectronic properties. Synthetic control over the solid state properties of organic optoe- 20 lectronic materials is crucial to access real life applications. Perylene diimides (PDIs) are one of the most highly studied classes of 21 organic fluorescent dyes. In the solid state, π-π stacking suppresses their emission, limiting their use in a variety of applications. Here 22 we report the synthesis of a novel PDI dye that is encapsulated by four alkylene straps. X-ray crystallography indicates that intermo- 23 lecular π-π stacking is completely suppressed in the crystalline state. This is further validated by the photophysical properties of the dye in both solution and solid state, and supported by theoretical calculations. However, we find that the introduction of the encap- 24 sulating ‘arms’ results in the creation of charge-transfer states which modify the excited state properties. This article demonstrates 25 that molecular encapsulation can be used as a powerful tool to tune intermolecular interactions and thereby gain an extra level of 26 control over the solid state properties of organic optoelectronic materials. 27 28 29 30 INTRODUCTION This can undesirably influence the photophysical properties of 11 31 Perylene diimides (PDIs) are one of the most highly studied the dye. 32 classes of organic fluorescent dyes.1 They were initially primar- Alternatively, it is also possible to shield the PDI core from 33 ily used as high-grade colorants in the pigment and textile in- intermolecular communication without disrupting its planarity 34 dustry, but have recently attracted great interest as materials for through functionalizing the imide positions with bulky substit- uents that shield both faces of the aromatic perylene.12 This 35 application in optoelectronic devices, such as organic solar cells (OSCs), light-emitting diodes (OLEDs), transistors and lasers.1– method was recently demonstrated by Wong and coworkers4. 36 3 The widespread use of PDI derivatives can be mainly at- They reported the synthesis of a series of PDI derivatives with 37 tributed to their desirable optoelectronic properties (e.g. high varying degrees of bulk on the imide positions, ranging from 38 photoluminescence quantum yields (PLQYs), tunable absorp- simple phenyl moieties to more congested 3,5-di-tert-bu- 39 tion and emission and high electron mobilities), photothermal tylphenyl and trityl groups.4 While their X-ray crystal data con- 40 stability and synthetic versatility.3 firm that increasing the bulk of the substituents leads to more 41 spatially shielded dyes, the UV-vis absorption data still indicate However, PDI chromophores have an inherently strong pro- 4 42 pensity to aggregate through π-π stacking.4 While sometimes significant aggregation for these molecules. Therefore, incor- 43 desirable for certain properties, such as charge transport, this porating bulky groups at the imide positions of PDIs does not 44 also limits their potential applications because it can greatly di- completely preclude the formation of aggregates, and hence 45 minish their photoluminesence at higher concentrations or in only offers limited control over their photophysical properties. 46 the solid state.4–6 As a result, it is extremely important to en- As a third option, we propose a strategy whereby the PDI core 47 hance our understanding of the structure-property relationships is surrounded by encapsulating alkylene straps, as has been demonstrated in other conjugated materials.13–22 This method 48 in PDIs towards obtaining higher levels of control over their aggregation behavior and photophysical properties in both the makes use of recently developed chemistry on the ortho-posi- 49 solution and solid state. tions (2,5,8,11) of PDIs23,24 to install 1,3-dimethoxybenzene 50 groups. These are then further functionalized to fully sheath the 51 Overall, there are three major strategies to suppress aggrega- tion through π-π stacking in PDI dyes. The first approach relies PDI core with two encapsulating rings. This article discusses 52 on the incorporation of steric bulk at the bay positions (1,6,7,12) the synthesis of a novel, doubly-encapsulated PDI and investi- 53 of the perylene core. Sterically demanding moieties can be in- gates the structural influence of molecular encapsulation on the 54 corporated via the facile nucleophilic aromatic substitution photophysical properties of the PDI chromophore. 55 (S Ar) of halogenated PDI cores.7,8 Although, incorporating N 56 steric hinderance at the bay positions reduces π-π stacking, it SYNTHESIS & CHARACTERIZATION 57 commonly imparts a twist in the planar aromatic PDI core.9,10 The synthesis of the doubly-encapsulated perylene diimide 58 (PDI-Encap) is demonstrated in Scheme 1. Perylene-3,4,9,10- 59 60 ACS Paragon Plus Environment The Journal of Organic Chemistry Page 2 of 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Scheme 1. Synthesis of the doubly-encapsulated perylene diimide (PDI-Encap). 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 1 1 1 56 Figure 1. (top) Fragment of H NMR spectra of PDI-OMe and PDI-Encap. (bottom left) H- H ROESY spectrum of PDI-Encap. 57 (bottom right) Structural NMR assignment. The shifts are reported in ppm and referenced against residual CHCl3 in CDCl3. 58 59 60 ACS Paragon Plus Environment Page 3 of 9 The Journal of Organic Chemistry tetracarboxylic dianhydride (PDA) was reacted with 2-oc- is in contrast to conventional PDI dyes that regularly engage in 1 tyldodecylamine to form the corresponding PDI (1) in 93% π-stacking in the crystalline state.26,27 Instead, it appears that the 2 yield after column chromatography. Upon iridium-catalyzed di- chromophore orientation is dictated by the crystallization of the 3 rect tetraborylation, PDI-BPin (2) was formed in a respectable encapsulating chains (Figure 4). The absence of π···π interac- 4 yield of 51%. During the direct borylation reaction, the catalyst tions in the PDI-Encap crystal structure is clearly attributable 5 is expected first to coordinate to one of the carbonyl oxygens, to steric hindrances caused by the peripheral aryl groups and the 6 which is then used to direct the BPin groups onto the ortho po- horizontally aligned alkylene chains. sitions of the perylene core through a concerted metalation 7 The structurally related tetra-arylated perylene (PDI-OMe) deprotonation.23 The cycle repeats itself until all four BPin crystallizes in the monoclinic P21/c space group with one PDI- 8 groups are installed.23 Further reaction with 2-bromo-1,3-di- 9 OMe and two CHCl3 molecules in the asymmetric unit. The methoxy-benzene under standard Suzuki-Miyaura cross cou- PDI-OMe molecules stack along the (011) Miller plane (Figure 10 pling conditions with Pd2dba3 and SPhos afforded the tetra-ar- 4), whereby its PDI cores display 10.2 Å centroid-to-centroid 11 ylated product PDI-OMe (3) in excellent yield (79%).