Article pubs.acs.org/joc
Microwave Synthesis of Thionated Naphthalene Diimide-Based Small Molecules and Polymers Paniz Pahlavanlu, Andrew J. Tilley, Bryony T. McAllister, and Dwight S. Seferos* Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada S Supporting Information *
ABSTRACT: Thionated naphthalene diimides (NDIs) are promising materials for n-type organic semiconductors; despite their potential, synthetic routes to thionated NDIs are generally lengthy, nonselective, and low yielding and their polymeric analogues have yet to be reported in the literature. Here, we describe the rapid and selective thionation of thiophene- and selenophene-flanked NDIs using microwave irradiation and excess Lawesson’s reagent. Remarkably, >99% conversion to the transdithionated product is observed by NMR within 45 min. Steric effects imparted by NDI core substituents prevent excess thionation, simplifying purification procedures. We apply this methodology to the postpolymerization thionation of NDI-based polymers to afford a series of polymers with varying degrees of thionation. Thionated NDIs exhibit bathochromic shifts of up to ∼100 nm in localized absorption maxima and increased electron affinities.
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INTRODUCTION
To this end, we synthesized a series of conjugated, coresubstituted NDI-based compounds that lend themselves to further functionalization or polymerization through terminating bromide groups (Figures 1 and S1). We compared thionation
Arylene diimides are among the most promising n-type organic semiconductors because they exhibit high electron affinity, high electron mobilities, and ambient stability.1−3 A further improvement in performance has been shown for their thioimide derivatives, which contribute larger coefficients to LUMOs and can improve electron affinity and intermolecular orbital overlap in the solid state through strong S−S interactions.4,5 Greater S−S intermolecular interactions can also compress solid-state packing, thereby reducing electron trapping and further promoting charge transport.4−7 Consequently, our group and others have shown that thionation of arylene diimides increases electron mobilities by up to 3 orders of magnitude5−8 and can improve ambient stability.5,8 Thionation of arylene diimides and structurally similar compounds has been investigated both in the absence of aromatic core substituents5−9 and in more structurally complex compounds.10−12 Notably, Ie et al. have reported the synthesis of arenedithiocarboxyimide dimers containing a conjugated covalent bridge,4 while Lévesque et al. have reported the effect of thionation in donor−acceptor−donor-type compounds involving 1,4-diketopyrrolopyrrole acceptor units.13 We wondered if we could employ thionation to modulate the optoelectronic properties of more extended conjugated systems, toward the synthesis of thionated arylene diimidebased polymers that remain elusive in the literature. In particular, we were interested in synthesizing thionated analogues of thiophene-flanked naphthalene diimides (NDIs)14,15 that have exhibited some of the highest electron mobilities of organic n-type materials.16 © 2017 American Chemical Society
Figure 1. Substrate scope for thionation studies. The rate and extent of thionation (X) are dictated by steric hindrance around thionation sites, invoked by a combination of bulky NDI core substituents (A) and branched alkyl chains (R). Full structures are available in the Supporting Information (Figure S1).
kinetics under traditional and microwave-assisted heating conditions to investigate the effect of core and imide substitution on the rate and selectivity of thionation. We applied optimized reaction parameters to the postpolymerization thionation of PNDIT2, a thiophene-flanked NDI-based polymer reported to exhibit an exceptional electron mobility.14 Finally, we investigated the effect of thionation on the electron Received: August 26, 2017 Published: October 26, 2017 12337
DOI: 10.1021/acs.joc.7b02162 J. Org. Chem. 2017, 82, 12337−12345
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It follows that thionation adjacent to the thiophene groups in Br-TNDIT-Br (2-OD) is sterically unfavorable, preventing the synthesis of cis-dithionated and higher order thionated products. We support this hypothesis through HMBC NMR experiments that illustrate exclusive coupling between naphthyl protons and neighboring thionyl carbons upon thionation (Figure 3a−c).11 To further elucidate the role of core substituents in the selective thionation of Br-TNDIT-Br (2-OD), we synthesized (Scheme S2) and monitored the microwave thionation of a model compound, NDI (2-OD), containing no core substituents. In the absence of core substituents, NDI (2-OD) thionation affords a mixture of products throughout the course of 1 h, including cis-S2 and S3 products (Figure 2b). We did not observe tetrathionation, which we attributed to the steric bulk imparted by alkyl branching at the 2-position of the imide substituent.7,8 A comparison of the thionation kinetics of NDI (2-OD) and Br-TNDIT-Br (2-OD) illustrates the utility of the latter compound. Selectivity invoked by bulky core substituents alleviates the synthetic challenges associated with arylene diimide thionation, namely the formation of a mixture of thionated products that must then be separated and purified through lengthy post-thionation procedures. Furthermore, moderately thionated arylene diimides benefit from improved solubility and have been shown to exhibit comparable, if not higher, electron mobilities in comparison to their higher order thionated analogues.6−8 Thus, a rapid and highly selective synthetic pathway toward trans-S2 NDI-based compounds is highly valuable. Having illustrated the importance of bulky core substituents in imparting synthetic selectivity, we wondered if thionation rates could be increased even further by decreasing the steric hindrance imparted by imide substituents, that is, by shifting alkyl branching positions further away from thionation sites. To that end, we synthesized a thiophene-flanked NDI incorporating a 3-hexylundecyl imide substituent, Br-TNDIT-Br (3-HU), and once again monitored the thionation kinetics (Figure 2c). Pleasingly, thionation kinetics increase 3-fold, reaching complete conversion to the trans-S2 product within just 15 min. We expect that thionation kinetics will increase further when using unbranched alkyl substituents, although this is expected to decrease the solubility of these compounds. While the focus of our study was on the synthesis of thionated thiophene-flanked NDIs, we wanted to determine whether our methodology could be extended to other NDIbased compounds of interest to the scientific community, namely the furan-24,25 and selenophene-flanked26,27 analogues of Br-TNDIT-Br (2-OD). Unfortunately, the furan-flanked analogue is photochemically unstable under ambient conditions, discolors when stored on the benchtop overnight, and decomposes rapidly in solution. The selenophene-flanked
affinities of NDI-based small molecules and polymers through optical absorption spectroscopy, cyclic voltammetry, and computational studies.
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RESULTS AND DISCUSSION Synthesis of Thionated Small Molecules. We synthesized Br-TNDIT-Br (2-OD), a bromothiophene-flanked NDI incorporating 2-octyldodecyl imide substituents, through adapted literature procedures (Scheme S1)17−21 and investigated its thionation using 5 mol equiv of Lawesson’s reagent in refluxing toluene.7,9 Thionation of the parent compound is evidenced by changes in naphthyl proton chemical shifts and splitting in crude 1H NMR spectra, and these peaks are then integrated, normalized, and compared to determine the relative composition of parent and thionated compounds in the crude mixture. Thionation proceeds slowly, reaching a near complete conversion to the trans-dithionated product after 3 days, while higher degrees of thionation were not observed. Slow thionation kinetics are not altogether surprising when considering the lengthy thionation procedures required for unsubstituted NDIs7,8 that bear significantly less steric bulk around thionation sites. Nonetheless, inspired by promising examples of microwave synthesis in the literature,22,23 we hypothesized that we could increase the rate and extent of thionation by heating the reaction mixture more efficiently and at higher temperatures using microwave irradiation. Again, we investigated Br-TNDIT-Br (2-OD) thionation kinetics using 5 mol equiv of Lawesson’s reagent, this time at 180 °C in a microwave reactor (Scheme 1). Remarkably, the Scheme 1. Microwave Thionation of Br-TNDIT-Br (2-OD)
parent compound (P) reacts rapidly to form about 45% monothionated product (S1) and 20% trans-dithionated product (trans-S2) within 5 min, reaching complete conversion to trans-S2 within 45 min (Figure 2a). We observed no trithionated product (S3) or tetrathionated product (S4), despite prolonged heating for up to 90 min in the presence of residual Lawesson’s reagent, nor did we observe the cisdithionated (cis-S2) product in the reaction mixture. Etheridge et al. have observed that carbonyl groups near the NDI core substituents do not undergo thionation due to steric hindrance. Likewise, Chen et al. have reported the selective cisdithionation of a thiophene-fused NDI at the distal carbonyls.
Figure 2. Microwave thionation kinetics of (a) Br-TNDIT-Br (2-OD), (b) NDI (2-OD), (c) Br-TNDIT-Br (3-HU), and (d) Br-SeNDISe-Br (2OD) using 5 mol equiv of Lawesson’s reagent at 180 °C, as measured through 1H NMR analysis of naphthyl core protons. 12338
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Figure 3. Low-field portion of HMBC NMR spectra of (a) P, (b) S1, and (c) trans-S2 Br-TNDIT-Br (2-OD). Bond coupling between naphthyl protons (HA, HA′) and neighboring carbons reflects the proximity of these protons to either carbonyl or thionyl carbons (∼160 and 190 ppm, respectively). α-Protons on the imide substituent (HB, HB′) serve as a frame of reference, since they are proximal to both carbonyl and thionyl carbons. Here, R = 1-octylundecyl.
Synthesis of Thionated Polymers. Motivated by the high degree of selectivity of our small molecule thionation studies, we wondered if we could directly apply our synthetic methodology to the postpolymerization thionation of PNDIT2. We envisioned extending our small molecule thionation kinetics to thionate PNDIT2 to varying degrees by varying the time frame of the reaction. For example, treating PNDIT2 with 5 mol equiv of Lawesson’s reagent at 180 °C for 1 h is expected to afford a polymer in which all the sterically unhindered carbonyls have been replaced with thionyl groups. Likewise, treating PNDIT2 for 5 min would afford a polymer with a statistical mixture of parent, monothionated, and transdithionated monomer units. In this way, we could quickly access a new class of polymer based on thionated NDIs and determine how thionation affects optoelectronic properties. To this end, we investigated the postpolymerization thionation of PNDIT2 (Scheme S3). The parent polymer was supplied as commercially available N2200 (Mn 36 kDa, Đ 3.3) by Flexterra Inc. and was used as received. We synthesized three thionated polymers by varying reaction times from 2.5 to 5 to 60 min, with the intention of reaching roughly 40% (S40PNDIT2), 60% (S60-PNDIT2), and 100% (S100-PNDIT2) thionation, where 100% thionation represents trans-dithionation of each monomer unit. To this end, PNDIT2 was treated with 5 mol equiv of Lawesson’s reagent in toluene under microwave irradiation (180 °C for 2.5, 5, and 60 min), to afford a series of thionated polymers. To determine the degree of thionation of each polymer, we first turned to 1H NMR spectroscopy, where clear spectral signatures for the different thionated derivatives allowed us to unambiguously assign the structures of the small molecule derivatives discussed earlier. However, the low solubility and broader peaks in the NMR spectra of both parent and partially thionated polymers prevented the quantitative determination of thionyl content by NMR analysis. We therefore turned to infrared (IR) spectroscopy to qualitatively assess the degree of thionation in the polymers, since carbonyls and thionyls exhibit distinct CO and CS vibrational stretching bands around 1670 and 1140 cm−1, respectively, and these measurements can be performed in the solid state. Since the structure and degree of thionation of the P, S1, and trans-S2 small molecules are well-defined, we used these compounds as a frame of reference for the thionated polymers. DFT frequency calculations on the optimized geometries of P, S1, and trans-S2 Br-TNDIT-Br (Me) predicted symmetric and asymmetric carbonyl stretches at 1754 and 1715 cm−1 for P and S1 Br-TNDIT-Br (2-OD) compounds (Figure S31), which appear in the experimentally obtained IR spectra at ∼1705 and ∼1665 cm−1 (Figure 4a,b,
analogue, Br-SeNDISe-Br (2-OD), is much more promising and was thus used for these studies. Thionation of BrSeNDISe-Br (2-OD) proceeds with similar kinetics to BrTNDIT-Br (2-OD), rapidly reacting to form the trans-S2 product within 1 h (Figure 2d). Having established thionation kinetics for Br-TNDIT-Br (2OD), Br-TNDIT-Br (3-HU), and Br-SeNDISe-Br (2-OD), we set out to synthesize and isolate S1 and trans-S2 analogues of each compound. The synthesis of trans-S2 compounds follows directly from the preceding kinetic studies: each parent compound was treated with 5 mol equiv of Lawesson’s reagent at 180 °C for either 1 h or 20 min (for 2-octyldodecyl and 3hexylundecyl substituted imides, respectively). Despite a near complete conversion to the trans-S2 product and no obvious sign of byproducts by crude 1H NMR analysis, isolated yields were only moderately high for each compound. For example, trans-S2 Br-TNDIT-Br (2-OD) was isolated in a 59% yield. Loss mechanisms are not immediately obvious since P, S1, and trans-S2 Br-TNDIT-Br (2-OD) all exhibit good thermal stability, up to at least 275 °C (95% decomposition for transS2) under a nitrogen atmosphere, as measured by thermogravimetric analysis (Figure S30). It is likely that the losses are a result of routine purification procedures. Optimization of synthetic parameters for the S1 synthesis required further research. From our previous thionation studies using 5 mol equiv of Lawesson’s reagent (Figure 2a), S1 BrTNDIT-Br (2-OD) reaches a maximum composition of about 45% after 5 min of heating, before being rapidly consumed to form the trans-S2 product. We wondered if we could obtain a higher S1 concentration in the crude mixture by decreasing the overall thionation kinetics, that is, by using 0.5 mol equiv of Lawesson’s reagent and decreasing the operating temperature. Despite investigating thionation kinetics at temperatures ranging from 50 to 180 °C, we again observed a maximum composition of about 45% S1 after 60 min of heating at 150 °C (Figure S2). Using these optimized conditions, each parent compound was treated with 0.5 mol equiv of Lawesson’s reagent at 150 °C for either 1 h or 20 min (for 2-octyldodecyl and 3-hexylundecyl substituted imides, respectively) and the P, S1, and trans-S2 compounds were separated through column chromatography. Interestingly, the isolated yields of each compound aligned well with crude compositions calculated from the 1H NMR spectra, after accounting for losses during purification; for example, isolated yields of P (34%), S1 (39%), and trans-S2 (13%) Br-TNDIT-Br (2-OD) were only slightly lower than those of the calculated crude compositions (40%, 45%, and 15% for P, S1, and trans-S2, respectively). 12339
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Figure 4. Infrared spectra of (a) P Br-TNDIT-Br (2-OD), (b) S1 Br-TNDIT-Br (2-OD), (c) trans-S2 Br-TNDIT-Br (2-OD), (d) PNDIT2, (e) S40PNDIT2, and (f) S60-PNDIT2, illustrating characteristic carbonyl (CO) and/or thionyl (CS) stretches.
Figure 5. Normalized solution absorption spectra of (a) P, S1, and trans-S2 Br-TNDIT-Br (2-OD) and (b) PNDIT2, S40-PNDIT2, and S60PNDIT2 in CHCl3. (c) Cyclic voltammetry plots of P, S1, and trans-S2 Br-TNDIT-Br (2-OD) in anhydrous dichloromethane (2.5 mM compound, 0.1 M TBAPF6).
respectively). In S1, the additional band at ∼1695 cm−1 is attributed to the carbonyl adjacent to the thionation site. The thionyl stretching band was observed at lower energies (∼1130 cm−1) and has a low oscillator strength, in agreement with the DFT predictions. Further thionation affords the trans-S2 compound that exhibits only one carbonyl stretching band, corresponding to a carbonyl adjacent to a thionyl group, and one thionyl stretching band (Figure 4c). Similar infrared spectra were observed for the Br-TNDIT-Br (3-HU) and BrSeNDISe-Br (2-OD) compounds (Figures S32 and S33). We observed similar carbonyl and thionyl stretching bands in the infrared spectra of the parent and thionated polymers. As expected, the infrared spectra of PNDIT2 exhibits carbonyl symmetric and asymmetric stretching bands (Figure 4d). We expected the infrared spectra of the partially thionated polymers to exhibit features corresponding to a mixture of parent and thionated diimides, like that of S1 Br-TNDIT-Br (2-OD) (Figure 4b). Thus, it is not unexpected that the infrared spectra of S40-PNDIT2 and S60-PNDIT2 contain both the symmetric (∼1705 cm−1) and asymmetric (∼1665 cm−1) carbonyl stretching bands of the parent polymer as well as the carbonyl (∼1695 cm−1) and thionyl (∼1130 cm−1) stretching bands associated with the onset of thionation (Figure 4e,f, respectively). Furthermore, the ratio of thionated to parent carbonyl stretching intensities increases in the infrared spectra
of S60-PNDIT2 relative to that of S40-PNDIT2, in agreement with the expected increase in degree of thionation. Perhaps not surprisingly,7 polymer solubility decreases drastically with increasing thionation; while S40-PNDIT2 and S60-PNDIT2 are fully soluble in refluxing chloroform and chlorobenzene, respectively, S100-PNDIT2 forms a gel in most organic solvents (Figure S3) and only dissolves with prolonged heating in 1,2,4-trichlorobenzene at 140 °C (1 mg/mL). While gel formation is in an interesting and somewhat unexpected phenomenon, which may suggest the formation of extended physical networks through S−S intermolecular interactions, it is beyond the scope of the present study. The remainder of our study thus focuses on the more soluble, lower order thionated polymers. Optoelectronic Properties and DFT Calculations. There are two main features in the optical absorption profiles of the parent and thionated Br-TNDIT-Br (2-OD) compounds: high-energy absorption bands exhibiting vibrational fine structure, characteristic of π−π* transitions of the NDI core,7,28 and lower energy, broader absorption bands, generally associated with intramolecular charge transfer interactions in core-substituted NDIs28−30 (Figure 5a). The absorption onset shifts bathochromically with increasing thionation, which has previously been reported for unsubstituted NDIs7,8 and perylene diimides.9 Interestingly, the S1 compound exhibits a significantly broader low-energy absorption band than that of 12340
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Table 1. Electrochemical Properties of P, S1, and trans-S2 Br-TNDIT-Br (2-OD)
either the parent or the trans-S2 compounds, which is an attractive feature for light-harvesting applications.31 We attribute this to the partial overlap of the high-energy absorption band, which shifts bathochromically with thionation,7,8 and the expected low-energy charge transfer band. We compared absorption spectra obtained in chloroform to that in cyclohexane and tetrahydrofuran (Figure S34) to identify solvatochromic effects associated with charge transfer interactions. Spectral variations are minimal, especially for the transS2 compound, which may indicate less intramolecular charge transfer character with increasing thionation in core-substituted NDIs. Lastly, we investigated photoluminescence of the parent and thionated compounds. Although a minor emission was observed for P Br-TNDIT-Br (2-OD), this sequentially decreased to near negligible intensities upon successive thionation to the S1 and trans-S2 compounds. Similar absorption and emission trends were observed for parent and thionated Br-TNDIT-Br (3-HU) and Br-SeNDISe-Br (2-OD) compounds (Figures S35 and S36). Significant fluorescence quenching has also been observed in other thionated NDI and perylene diimide derivatives and is attributed to rapid intersystem crossing to triplet states.9 We next investigated the optical absorption properties of parent and thionated polymers. The optical absorption spectrum of PNDIT2 features high- and low-energy bands corresponding, again, to π−π* transitions and intramolecular charge transfer interactions (Figure 5b).32 S40-PNDIT2 and S60-PNDIT2 absorption profiles are similar but are bathochromically shifted. Notably, the lower energy absorption maxima shift from 662 to 719 nm to 745 nm for PNDIT2, S40PNDIT2, and S60-PNDIT2, respectively, is consistent with increasing thionation. The n-type materials that absorb nearinfrared radiation are particularly useful acceptors for organic photovoltaics since they are able to absorb a greater portion of the solar spectrum.12 These preliminary findings illustrate the effect of even moderate degrees of thionation for achieving desirable optoelectronic properties for NDI-based polymers. Next, we investigated the redox properties of parent and thionated Br-TNDIT-Br (2-OD) through cyclic voltammetry in 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) in dry dichloromethane (Figure 5c). All three compounds exhibit two reversible reduction waves, which shift to more positive potentials upon thionation. The first half-width reduction potentials (ER1,1/2) increase from −1.01 V to −0.96 V to −0.77 V for the parent, monothionated, and dithionated compounds, respectively. We estimated the LUMO levels from ER1,1/2, while the HOMO levels were estimated from the absorption onset (Table 1). In agreement with the literature, the LUMO energy levels decrease appreciably upon thionation, from −4.09 eV for the parent compound to −4.33 eV for the trans-S2 compound. DFT calculations indicate increased LUMO contributions from sulfur atoms, in contrast to oxygen atoms, in S1 and trans-S2 Br-TNDIT-Br (Me) (Figure S37), which may account for the depression in the LUMO energy levels upon thionation. There is no clear trend in the experimentally derived HOMO levels, while DFT calculated HOMO levels remain approximately constant. The increased electron affinity of thionated thiophene-flanked NDIs coupled with the red-shifted absorption bodes well for the continued development of thionated NDI-based dyes as n-type materials for electronics applications.
P S1 trans-S2
ER1,1/2a (V)
ER2,1/2a (V)
EHOMOb,c (eV)
ELUMOb,d (eV)
−1.01 −0.96 −0.77
−1.47 −1.35 −1.09
−6.16 (−6.41) −6.05 (−6.41) −6.15 (−6.42)
−4.09 (−3.86) −4.14 (−3.99) −4.33 (−4.11)
ER1,1/2 and ER2,1/2 are the first and second half-width reduction potentials, respectively, obtained by cyclic voltammetry referenced to the Fc/Fc+ redox couple. bDFT calculated orbital energies are included in brackets below experimentally obtained energies. cEHOMO = ELUMO − Eg,opt where Eg,opt is the optical energy gap calculated from the absorption onset by optical absorption spectroscopy. dELUMO = −(ER1,1/2 + 5.1) where ER1,1/2 is the energy associated with the first half-width reduction potential. a
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CONCLUSIONS We have developed a well-defined synthetic methodology for the rapid and selective thionation of thiophene- and selenophene-flanked NDIs using carefully controlled quantities of Lawesson’s reagent and microwave-assisted heating. Steric hindrance imparted by bulky core and imide substituents prevents thionation at neighboring carbonyls, allowing selective conversion to the trans-S2 product in as little as 15 min. Our methodology is a significant improvement over existing routes to thionated NDIs and is readily adapted toward the facile synthesis of thionated NDI-based polymers through postpolymerization modification. Thionated NDIs exhibit bathochromically shifted absorption profiles and increased electron affinities. Notably, even moderately thionated polymers absorb into the near-infrared region. These results render thionation as a rapid and accessible strategy for modifying the optoelectronic properties of NDI-based small molecules and polymers.
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EXPERIMENTAL SECTION
Materials. 3-Hexylundecylamine 9 and 2-(tributylstannyl)selenophene21 were synthesized through literature procedures. 2,6Dibromonaphthalene-1,4,5,8-tetracarboxylic dianhydride (Br-NDABr) was synthesized through a literature procedure,18 collected as a crude mixture of brominated products, characterized through 1H NMR analysis,19 and used without further modification. 2Octyldodecylamine was purchased from Lyntech Co., Ltd. The parent polymer (PNDIT2, Mn 36 kDa, Đ 3.3) was provided by Flexterra Inc. and was used as received. Lawesson’s reagent was purchased from Sigma-Aldrich and recrystallized from toluene prior to use. Dry toluene, dichloromethane, N,N-dimethylformamide, and tetrahydrofuran were obtained from an Innovative Technology PureSolv solvent purification system. Schlenk techniques were employed for experiments conducted under argon. Experimental Methods. Nuclear magnetic resonance spectra were obtained using a Varian Mercury 400 spectrometer (crude samples) or an Agilent DD2 500 spectrometer (pure compounds) and were referenced to residual chloroform. All compounds were characterized by 1H and 13C NMR spectroscopy, while parent and thionated analogues of Br-TNDIT-Br (2-OD), Br-TNDIT-Br (3-HU), and Br-SeNDISe-Br (2-OD) were further characterized by 2D NMR spectroscopy (COSY and HMBC). Mass spectra were recorded on a Bruker Autoflex Speed MALDI-TOF mass spectrometer using direct laser desorption ionization (LDI-TOF). Polymer molecular weights were determined through gel permeation chromatography using a Viscotek HT-GPC in 1,2,4-trichlorobenzene at 140 °C (1 mL/min flow rate). Microwave reactions were conducted in a Biotage Initiator synthetic microwave in sealed reaction vials, and the temperature was monitored using an external surface sensor. Fourier transform infrared (FT-IR) spectroscopy was performed using a PerkinElmer Spectrum 12341
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The Journal of Organic Chemistry
was synthesized through an adapted literature procedure.39 Under an argon atmosphere, 2-octyldodecylamine (10.5 g, 35.4 mmol) was added to Br-NDA-Br (3.5 g, 50% Br-NDA-Br) in glacial acetic acid (100 mL) and the mixture was stirred at 120 °C for 3 h. The solution was concentrated in vacuo; methanol (40 mL) was added, and the resulting red precipitate was collected by filtration. Purification by column chromatography (1:1 v/v CH2Cl2/hexanes) and recrystallization from hexanes afforded a yellow crystalline solid. Yield: 2.6 g, 59% (relative to 50% Br-NDA-Br); mp 83.7−85.9 °C. Anal. Calcd for C54H84N2Br2O4: C, 65.84; H, 8.60; N, 2.84. Found: C, 65.58; H, 8.65; N, 2.92. 2,6-Dibromonaphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(3hexylundecyl) Diimide (Br-NDI-Br (3-HU)). Under an argon atmosphere, 3-hexylundecylamine (5.7 g, 22.5 mmol) was added to Br-NDA-Br (3.2 g, 30% Br-NDA-Br) in glacial acetic acid (85 mL) and the mixture was stirred at 120 °C for 3 h. Precipitation into methanol (200 mL) produced a red solid that was collected by filtration. Purification by column chromatography (1:1 v/v CH2Cl2/hexanes) and recrystallization from hexanes afforded a yellow crystalline solid. Yield: 0.63 g, 26% (relative to 30% Br-NDA-Br); mp 123.6−125.3 °C. 1 H NMR (500 MHz, CDCl3): δ 8.99 (s, 2H), 4.15−4.24 (m, 4H), 1.61−1.72 (m, 4H), 1.43−1.51 (m, 2H), 1.20−1.39 (m, 48H), 0.88, 0.89 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 160.64, 160.59, 139.0, 128.2, 127.7, 125.3, 124.1, 40.0, 36.0, 33.53, 33.51, 31.91, 31.88, 31.7, 30.04, 29.71, 29.6, 29.4, 26.58, 26.55, 22.7, 14.1. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C48H72Br2N2O4H, 899.39; found, 899.08. Anal. Calcd for C48H72Br2N2O4: C, 63.99; H, 8.06; N, 3.11. Found: C, 63.93; H, 8.02; N, 3.16. 2,6-Bis(2-thienyl)naphthalene-1,4,5,8-tetracarboxylic-N,N′bis(2-octyldodecyl) Diimide (TNDIT (2-OD)). TNDIT (2-OD) was synthesized through an adapted literature procedure.20 Under an argon atmosphere, 2-(tributylstannyl)thiophene (1.6 mL, 5.0 mmol) was added to Br-NDI-Br (2-OD) (2.0 g, 2.0 mmol) and bis(triphenylphosphine)palladium(II) dichloride (Pd(PPh3)2Cl2, 0.06 g, 0.09 mmol) in tetrahydrofuran (50 mL). The mixture was heated to reflux overnight; then the solvent was removed in vacuo. The crude product was recrystallized from isopropanol and filtered through silica with CH2Cl2 before concentration in vacuo to afford an orange crystalline solid. Yield: 2.0 g, 99%; mp 65.4−68.1 °C. 1H NMR (500 MHz, CDCl3): δ 8.76 (s, 2H), 7.56 (dd, J = 5.1, 1.2 Hz, 2H), 7.29 (dd, J = 3.6, 1.2 Hz, 2H), 7.19 (dd, J = 5.1, 3.6 Hz, 2H), 4.06 (d, J = 7.4 Hz, 4H), 1.90−2.00 (m, 2H), 1.17−1.41 (m, 64H), 0.85, 0.86 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 162.5, 162.4, 140.8, 140.2, 136.6, 128.2, 128.0, 127.5, 127.4, 125.4, 123.4, 44.9, 36.4, 31.89, 31.87, 31.6, 31.5, 30.04, 30.03, 29.64, 29.61, 29.6, 29.5, 29.32, 29.29, 26.4, 22.7, 22.6, 14.1, 13.6. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C 62 H 90 N 2 O 4 S 2 H, 991.64; found, 991.38. Anal. Calcd for C62H90N2O4S2: C, 75.10; H, 9.15; N, 2.83. Found: C, 75.21; H, 9.33; N, 2.70. 2,6-Bis(2-thienyl)naphthalene-1,4,5,8-tetracarboxylic-N,N′bis(3-hexylundecyl) Diimide (TNDIT (3-HU)). Under an argon atmosphere, 2-(tributylstannyl)thiophene (0.7 g, 1.8 mmol) was added to Br-NDI-Br (3-HU) (0.7 g, 0.8 mmol) and Pd(PPh3)2Cl2 (0.01 g, 0.02 mmol) in tetrahydrofuran (20 mL). The mixture was heated to reflux overnight; then the solvent was removed in vacuo. The crude product was recrystallized from isopropanol, redissolved in CH2Cl2, and filtered before concentration in vacuo to afford an orange-red crystalline solid. Yield: 0.6 g, 88%; mp 98.7−100.3 °C. 1H NMR (500 MHz, CDCl3): δ 8.75 (s, 2H), 7.57 (dd, J = 5.0, 1.2 Hz, 2H), 7.30 (dd, J = 3.6, 1.2 Hz, 2H), 7.20 (dd, J = 5.1, 3.5 Hz, 2H), 4.07−4.16 (m, 4H), 1.57−1.66 (m, 4H), 1.37−1.45 (m, 2H), 1.18−1.36 (m, 48H), 0.87 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 162.1, 161.9, 140.7, 140.2, 136.6, 128.3, 127.9, 127.42, 127.35, 125.4, 123.4, 39.5, 36.0, 33.5, 31.90, 31.88, 30.1, 29.7, 29.6, 29.3, 26.54, 26.49, 22.7, 14.1. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C56H78N2O4S2H, 907.55; found, 907.52. Anal. Calcd for C56H78N2O4S2: C, 74.13; H, 8.67; N, 3.09. Found: C, 73.93; H, 8.74; N, 3.01. 2,6-Bis(2-selenophyl)naphthalene-1,4,5,8-tetracarboxylicN,N′-bis(2-octyldodecyl) Diimide (SeNDISe (2-OD)). Under an argon atmosphere, 2-(tributylstannyl)selenophene (1.0 g, 2.5 mmol)
100 FT-IR spectrometer equipped with an attenuated total reflection (ATR) crystal. Melting points for crystalline compounds were measured using a Fischer-Johns melting point apparatus. Thermogravimetric analysis (TGA) was conducted at a scan rate of 10 °C/min under nitrogen using a TA Instruments Q50 TGA. Optical micrographs were collected using a Zeiss Microscope Axio Imager A2M optical microscope. Thionation kinetics were measured through 1H NMR analysis of naphthalene core protons (δ 8.6−7.1) in crude thionation samples. Proton peaks were assigned on the basis of literature values for the dodecyl 7 and 2-ethylhexyl 8 analogues of NDI (2-OD) and experimentally obtained values of Br-TNDIT-Br (2-OD), BrTNDIT-Br (3-HU), and Br-SeNDISe-Br (2-OD). Proton peaks were integrated and scaled relative to the number of protons contributing to the peak. The percentage composition of each NDIbased compound in the crude mixture was calculated by comparing scaled integrations for the compound to the sum of scaled integrations for the crude mixture. To ensure consistent heating in the microwave reactor, individual samples were prepared for each data point of the kinetic study and heated for the designated reaction time. Optical absorption spectra were obtained using a Varian Cary 5000 UV−vis-NIR spectrophotometer. Optical absorption maxima (λmax) are reported for the low-energy absorption bands of each compound. Photoluminescence spectra were measured with a PTI QuantaMaster 40-F NA spectrofluorometer with a xenon arc lamp source and a photomultiplier detector using λex = 450 nm, while maintaining optical densities below 0.2 to limit reabsorption effects. Cyclic voltammetry (CV) was performed using a BioLogic SP-200 Potentiostat/ Galvanostat/Frequency Response Analyzer with a platinum button working electrode, a silver wire pseudoreference electrode, and a platinum mesh counter electrode. CV experiments were conducted under an argon atmosphere, in dry dichloromethane (2.5 mM compound, 0.1 M tetrabutylammonium hexafluorophosphate electrolyte) with a scan rate of 50 mV/s and referenced to the Fc/Fc+ redox couple. The second of three redox cycles is reported. Electrochemical data were calculated from optical absorption and CV data. The first and second half-width reduction potentials (ER1,1/2 and ER2,1/2, respectively) were calculated as the average of the cathodic and anodic peak potentials for each redox couple. LUMO energies were estimated from the first half-width reduction energy (ER1,1/2) and converted to the vacuum scale using the equation ELUMO = −(ER1,1/2 + 5.1).33 HOMO energies (EHOMO) were estimated from the LUMO energy (ELUMO) and the optical energy gap (Eg,opt),7 and the latter of which was calculated from the absorption onset in solution. Computational Methods. Density functional theory (DFT) calculations were performed with Gaussian 09,34 using GaussView 535 to generate structures. Geometry optimizations and subsequent frequency calculations were carried out using the B3LYP36,37 functional with the 6-311+G(d)38 basis set. Frequencies were analyzed as calculated. All energy levels were converted from hartree to eV units. Naphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(2-octyldodecyl) Diimide (NDI (2-OD)). Under an argon atmosphere, naphthalene1,4,5,8-tetracarboxylic dianhydride (1.0 g, 3.7 mmol) and 2octyldodecylamine (4.4 g, 14.8 mmol) were heated to reflux in N,Ndimethylformamide (50 mL) for 29 h. The crude mixture was cooled, and the resulting gray precipitate was collected by filtration and washed with methanol. Purification by column chromatography (1:1 v/v CH2Cl2/hexanes) yielded a yellow oil, which was diluted with CH2Cl2, precipitated into methanol, and filtered to afford a white crystalline solid. Yield: 0.9 g, 30%; mp 51.1−51.8 °C. 1H NMR (500 MHz, CDCl3): δ 8.76 (s, 4H), 4.13 (d, J = 7.3 Hz, 4H), 1.93−2.03 (m, 2H), 1.16−1.45 (m, 64H), 0.85, 0.86 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 163.3, 131.2, 126.9, 126.7, 45.1, 36.8, 32.1, 32.0, 31.80, 31.79, 30.2, 29.77, 29.76, 29.74, 29.69, 29.5, 29.4, 26.6, 22.83, 22.80, 14.26, 14.25. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C54H86N2O4H, 827.67; found, 827.65. Anal. Calcd for C54H86N2O4: C, 78.40; H, 10.48; N, 3.39. Found: C, 78.09; H, 10.55; N, 3.49. 2,6-Dibromonaphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(2octyldodecyl) Diimide (Br-NDI-Br (2-OD)). Br-NDI-Br (2-OD) 12342
DOI: 10.1021/acs.joc.7b02162 J. Org. Chem. 2017, 82, 12337−12345
Article
The Journal of Organic Chemistry
59.65; H, 7.17; N, 2.28. FT-IR (neat, cm−1): 1702 (vCO,sym), 1665 (vCO,asym). Optical absorption (CHCl3): λmax = 505 nm. General Procedure for Thionation Kinetic Studies. Parent compound (0.032 mmol), Lawesson’s reagent (0.17 or 0.02 mmol), and a stir bar were dried in vacuo in a sealed microwave vial for 30 min. The reaction vessel was backfilled with argon, and dry toluene (2 mL) was added by syringe. In a microwave reactor, the reaction mixture was heated up at maximum power (400 W); then the temperature was maintained at the designated temperature (e.g., 180 °C) for the designated reaction time (e.g., 5 min). Toluene was removed in vacuo, and the crude sample was analyzed by 1H NMR. General Procedure for S1 Synthesis. Parent compound (0.08 mmol), Lawesson’s reagent (0.04 mmol), and a stir bar were dried in vacuo in a sealed microwave vial for 30 min. The reaction vessel was backfilled with argon, and dry toluene (5 mL) was added by syringe. In a microwave reactor, the reaction mixture was heated up at maximum power (400W); then the temperature was maintained at 150 °C for 1 h (R = 2-OD) or 20 min (R = 3-HU). Toluene was removed in vacuo. The crude product was redissolved in chloroform (2 mL), precipitated into methanol (10 mL), and collected by filtration. Parent compound, S1, and trans-S2 were separated by column chromatography (1:3 v/v CH2Cl2/hexanes for trans-S2, then 1:1 v/v CH2Cl2/hexanes for S1, then CH2Cl2 for P). trans-S2 was further purified by recrystallization from anhydrous ethanol. S1 Br-TNDIT-Br (2-OD). The product was obtained as a purple amorphous solid. Crude composition (by 1H NMR): 40% P, 45% S1, 15% trans-S2. Isolated yield: 0.03 g, 34% P, 0.04 g, 39% S1, 0.01 g, 13% trans-S2. 1H NMR (500 MHz, CDCl3): δ 9.01 (s, 1H), 8.69 (s, 1H), 7.14 (d, J = 3.9, 2H), 7.09 (d, J = 3.9, 1H), 7.07 (d, J = 3.8, 1H), 4.63 (d, J = 7.4 Hz, 2H), 4.05 (d, J = 7.4 Hz, 2H), 2.13−2.24 (m, 1H), 1.87−1.99 (m, 1H), 1.12−1.45 (m, 64H), 0.86, 0.87 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 192.1, 162.64, 162.60, 160.2, 142.6, 142.5, 141.5, 139.3, 138.5, 136.3, 130.4, 130.3, 129.2, 128.92, 128.85, 127.7, 126.0, 125.6, 123.3, 122.1, 115.8, 115.4, 51.6, 45.1, 36.6, 35.6, 32.1, 32.0, 31.8, 31.7, 30.22, 30.21, 29.9, 29.82, 29.79, 29.77, 29.7, 29.50, 29.47, 26.53, 26.49, 22.84, 22.82, 14.3. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C62H88Br2N2O3S3H, 1163.44; found, 1163.00. Anal. Calcd for C62H88Br2N2O3S3: C, 63.90; H, 7.61; N, 2.40. Found: C, 64.28; H, 7.72; N, 2.40. FT-IR (neat, cm−1): 1704 (vCO,sym), 1697 (vCO), 1667 (vCO,asym), 1134 (vCS). Optical absorption (CHCl3): λmax = 446 nm. S1 Br-TNDIT-Br (3-HU). The product was obtained as a purple amorphous solid. Crude composition (by 1H NMR): 46% P, 43% S1, 11% trans-S2. Isolated yield: 0.02 g, 42% P, 0.02 g, 41% S1, 0.002 g, 4% trans-S2 from 0.05 mmol Br-TNDIT-Br (3-HU). 1H NMR (500 MHz, CDCl3): δ 9.03 (s, 1H), 8.69 (s, 1H), 7.15 (2 d, J = 3.8, 2H), 7.11 (d, J = 3.8, 1H), 7.08 (d, J = 3.8, 1H), 4.59−4.67 (m, 2H), 4.07−4.15 (m, 2H), 1.65−1.73 (m, 2H), 1.57−1.65 (m, 2H), 1.38−1.50 (m, 2H), 1.21−1.37 (m, 48H), 0.85−0.92 (m, 12H). 13C NMR (126 MHz, CDCl3): δ 191.3, 162.1, 162.0, 159.2, 142.3, 142.2, 141.3, 139.1, 138.3, 136.1, 130.2, 130.1, 129.0, 128.9, 128.8, 127.5, 125.9, 125.5, 123.2, 122.0, 115.7, 115.2, 46.8, 39.5, 36.2, 35.9, 33.5, 31.92, 31.89, 31.8, 30.3, 30.1, 30.0, 29.72, 29.70, 29.65, 29.6, 29.4, 26.63, 26.57, 26.56, 26.5, 22.70, 22.68, 14.14, 14.12. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C56H76Br2N2O3S3H, 1079.35; found, 1079.31. Anal. Calcd for C56H76Br2N2O3S3: C, 62.21; H, 7.09; N, 2.59. Found: C, 61.92; H, 7.16; N, 2.57. FT-IR (neat, cm−1): 1702 (vCO,sym), 1693 (vCO), 1665 (vCO,asym), 1133 (vCS). Optical absorption (CHCl3): λmax = 445 nm. S1 Br-SeNDISe-Br (2-OD). The product was obtained as a purple amorphous solid. Crude composition (by 1H NMR): 43% P, 45% S1, 12% trans-S2. Isolated yield: 0.04 g, 37% P, 0.03 g, 26% S1, 0.008 g, 8% trans-S2. 1H NMR (500 MHz, CDCl3): δ 9.07 (s, 1H), 8.73 (s, 1H), 7.36 (2 d, J = 4.1, 2H), 7.26 (d, J = 4.1, 1H), 7.23 (d, J = 4.2, 1H), 4.63 (d, J = 7.4 Hz, 2H), 4.06 (d, J = 7.3 Hz, 2H), 2.12−2.23 (m, 1H), 1.87−1.98 (m, 1H), 1.14−1.41 (m, 64H), 0.85, 0.87 (2 t, J = 6.9 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 192.0, 162.9, 162.5, 160.5, 148.1, 147.8, 141.5, 141.0, 140.6, 135.8, 133.1, 133.0, 131.4, 131.2, 129.0, 127.3, 125.7, 125.3, 122.3, 121.1, 120.9, 120.3, 51.4, 44.9, 36.5, 35.4, 31.90, 31.89, 31.62, 31.56, 30.1, 30.0, 29.7, 29.63, 29.61, 29.56,
was added to Br-NDI-Br (2-OD) (1.0 g, 1.0 mmol) and Pd(PPh3)2Cl2 (0.06 g, 0.09 mmol) in tetrahydrofuran (25 mL). The mixture was heated to reflux overnight; then the solvent was removed in vacuo. The crude product was washed with isopropanol and filtered through silica with CH2Cl2 before concentration in vacuo to afford an orangered crystalline solid. Yield: 1.1 g, 99%; mp 71.4−73.1 °C. 1H NMR (500 MHz, CDCl3): δ 8.76 (s, 2H), 8.27 (dd, J = 5.0, 1.7 Hz, 2H), 7.40−7.44 (m, 4H), 4.07 (d, J = 7.4 Hz, 4H), 1.89−2.01 (m, 2H), 1.16−1.42 (m, 64H), 0.86, 0.87 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 162.6, 162.5, 146.8, 142.5, 136.4, 134.0, 130.4, 129.7, 127.4, 125.2, 122.9, 44.9, 36.5, 31.89, 31.88, 31.57, 31.55, 30.1, 30.0, 29.7, 29.62, 29.60, 29.5, 29.33, 29.30, 27.4, 22.66, 22.65, 14.1. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C62H90N2O4Se2H, 1087.53; found, 1087.76. Anal. Calcd for C62H90N2O4Se2: C, 68.61; H, 8.36; N, 2.58. Found: C, 68.41; H, 8.38; N, 2.63. 2,6-Bis(2-bromothien-5-yl)naphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(2-octyldodecyl) Diimide (Br-TNDIT-Br (2-OD)). BrTNDIT-Br (2-OD) was synthesized through an adapted literature procedure.20 TNDIT (2-OD) (2.0 g, 2.0 mmol) and N-bromosuccinimide (1.1 g, 6.0 mmol) were heated in glacial acetic acid/chloroform (1:1 v/v, 120 mL) at 60 °C for 27 h. Chloroform was removed in vacuo, and the resulting red precipitate was collected by filtration and washed with methanol. Recrystallization from anhydrous ethanol (650 mL) afforded a red crystalline solid. Yield: 1.8 g, 79%; mp 105.5−107.2 °C. 1H NMR (500 MHz, CDCl3): δ 8.72 (s, 2H), 7.14 (d, J = 3.9 Hz, 2H), 7.08 (d, J = 3.8 Hz, 2H), 4.07 (d, J = 7.4 Hz, 4H), 1.89−1.99 (m, 2H), 1.16−1.42 (m, 64H), 0.85, 0.87 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 162.30, 162.27, 142.1, 139.0, 136.4, 130.2, 128.8, 127.5, 125.6, 123.1, 115.5, 45.0, 36.5, 31.89, 31.87, 31.5, 30.0, 29.64, 29.62, 29.60, 29.5, 29.33, 29.29, 26.3, 22.67, 22.65, 14.1. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C62H88Br2N2O4S2H, 1147.46; found, 1147.65. Anal. Calcd for C62H88Br2N2O4S2: C, 64.79; H, 7.72; N, 2.44. Found: C, 64.85; H, 7.69; N, 2.42. FT-IR (neat, cm−1): 1705 (vCO,sym), 1666 (vCO,asym). Optical absorption (CHCl3): λmax = 495 nm. 2,6-Bis(2-bromothien-5-yl)naphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(3-hexylundecyl) Diimide (Br-TNDIT-Br (3-HU)). TNDIT (3-HU) (0.5 g, 0.5 mmol) and N-bromosuccinimide (0.3 g, 1.5 mmol) were heated in glacial acetic acid/chloroform (1:1 v/v, 30 mL) at 60 °C for 24 h. Chloroform was removed in vacuo, and the resulting red precipitate was collected by filtration and washed with acetic acid, methanol, and anhydrous ethanol. The product was washed three times in boiling anhydrous ethanol and filtered to afford a red crystalline solid. Yield: 0.4 g, 71%; mp 105.9−108.1 °C. 1H NMR (500 MHz, CDCl3): δ 8.72 (s, 2H), 7.15 (d, J = 3.9, 2H), 7.09 (d, J = 3.9, 2H), 4.07−4.17 (m, 4H), 1.58−1.65 (m, 4H), 1.37−1.46 (m, 2H), 1.20−1.36 (m, 48H), 0.87 (2 t, J = 6.9 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 161.9, 161.8, 142.0, 139.0, 136.4, 130.1, 128.9, 127.5, 125.6, 123.2, 115.4, 39.6, 35.9, 33.5, 31.90, 31.88, 31.85, 30.1, 29.7, 29.6, 29.3, 26.6, 26.5, 22.7, 14.1. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C56H76Br2N2O4S2H, 1063.37; found, 1063.32. Anal. Calcd for C56H76Br2N2O4S2: C, 63.15; H, 7.19; N, 2.63. Found: C, 62.46; H, 7.42; N, 2.57. FT-IR (neat, cm−1): 1704 (vCO,sym), 1665 (vCO,asym). Optical absorption (CHCl3): λmax = 494 nm. 2,6-Bis(2-bromoselenoph-5-yl)naphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(2-octyldodecyl) Diimide (Br-SeNDISe-Br (2OD)). SeNDISe (2-OD) (0.7 g, 0.7 mmol) and N-bromosuccinimide (0.4 g, 2.0 mmol) were heated in glacial acetic acid/chloroform (1:1 v/ v, 40 mL) at 60 °C for 3 h. Chloroform was removed in vacuo, and the resulting red precipitate was collected by filtration and washed with methanol. Recrystallization from anhydrous ethanol afforded an orange-red crystalline solid. Yield: 0.6 g, 76%; mp 81.3−83.0 °C. 1H NMR (500 MHz, CDCl3): δ 8.77 (s, 2H), 7.36 (d, J = 4.1, 2H), 7.25 (d, J = 4.1, 2H), 4.09 (d, J = 7.4 Hz, 4H), 1.89−2.00 (m, 2H), 1.15− 1.43 (m, 64H), 0.85, 0.87 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 162.7, 162.4, 147.7, 141.3, 136.0, 133.0, 131.4, 127.3, 125.5, 122.2, 120.6, 36.5, 31.90, 31.88, 31.6, 30.0, 29.7, 29.63, 29.61, 29.55, 29.33, 29.31, 26.3, 22.67, 22.66, 14.1. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C62H88Br2N2O4Se2H, 1243.23; found, 1243.35. Anal. Calcd for C62H88Br2N2O4Se2: C, 59.90; H, 7.14; N, 2.25. Found: C, 12343
DOI: 10.1021/acs.joc.7b02162 J. Org. Chem. 2017, 82, 12337−12345
Article
The Journal of Organic Chemistry 29.34, 29.32, 26.4, 26.3, 22.68, 22.66, 14.11. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C62H88Br2N2O3SSe2H, 1259.33; found, 1259.76. Anal. Calcd for C62H88Br2N2O3SSe2: C, 59.14; H, 7.04; N, 2.22. Found: C, 58.69; H, 7.10; N, 2.16. FT-IR (neat, cm−1): 1704 (vCO,sym), 1686 (vCO), 1665 (vCO,asym), 1127 (vCS). Optical absorption (CHCl3): λmax = 446 nm. General Procedure for trans-S2 Synthesis. Parent compound (0.08 mmol), Lawesson’s reagent (0.40 mmol), and a stir bar were dried in vacuo in a sealed microwave vial for 30 min. The reaction vessel was backfilled with argon, and dry toluene (5 mL) was added by syringe. In a microwave reactor, the mixture was heated up at maximum power (400W); then the temperature was maintained at 180 °C for 1 h (R = 2-OD) or 20 min (R = 3-HU). Toluene was removed in vacuo. The crude product was redissolved in chloroform (2 mL), precipitated into methanol (10 mL), and collected by filtration. The product was washed with hexanes on a silica plug before recrystallization from anhydrous ethanol. trans-S2 Br-TNDIT-Br (2-OD). The product was obtained as a purple amorphous solid. Crude composition (by 1H NMR): 99%. Isolated yield: 0.06 g, 59%. 1H NMR (500 MHz, CDCl3): δ 8.96 (s, 2H), 7.13 (d, J = 3.8, 2H), 7.06 (d, J = 3.8, 2H), 4.58 (d, J = 7.4 Hz, 4H), 2.11−2.22 (m, 2H), 1.16−1.40 (m, 64H), 0.86, 0.87 (2 t, J = 6.8 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 191.9, 160.2, 142.5, 141.1, 138.3, 130.2, 128.7, 128.6, 125.8, 122.0, 115.4, 51.4, 35.4, 31.92, 31.89, 31.63, 31.62, 30.1, 29.7, 29.64, 29.62, 29.57, 29.4, 29.3, 26.4, 22.69, 22.68, 14.12. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C62H88Br2N2O2S4H, 1179.42; found, 1179.40. Anal. Calcd for C62H88Br2N2O2S4: C, 63.03; H, 7.51; N, 2.37. Found: C, 62.98; H, 7.64; N, 2.31. FT-IR (neat, cm−1): 1694 (vCO), 1131 (vCS). Optical absorption (CHCl3): λmax = 489 nm. trans-S2 Br-TNDIT-Br (3-HU). The product was obtained as a purple amorphous solid. Crude composition (by 1H NMR): 99%. Isolated yield: 0.02 g, 42% from 0.05 mmol Br-TNDIT-Br (3-HU). 1H NMR (500 MHz, CDCl3): δ 9.00 (s, 2H), 7.15 (d, J = 3.8, 2H), 7.09 (d, J = 3.8, 2H), 4.58−4.65 (m, 4H), 1.64−1.72 (m, 4H), 1.41−1.49 (m, 2H), 1.20−1.36 (m, 48H), 0.88, 0.89 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 191.4, 159.4, 142.5, 141.1, 138.3, 130.2, 128.9, 128.6, 125.9, 122.1, 115.4, 46.8, 36.2, 33.5, 31.9, 30.3, 30.1, 29.71, 29.69, 29.66, 29.4, 26.64, 26.57, 22.70, 22.69, 14.14. LRMS (LDI-TOF) m/z: [M + H]+ calcd for C56H76Br2N2O2S4H, 1095.32; found, 1095.13. Anal. Calcd for C56H76Br2N2O2S4: C, 61.30; H, 6.98; N, 2.55. Found: C, 61.90; H, 7.28; N, 2.47. FT-IR (neat, cm−1): 1689 (vCO), 1127 (vCS). Optical absorption (CHCl3): λmax = 488 nm. trans-S2 Br-SeNDISe-Br (2-OD). The product was obtained as a purple amorphous solid. Crude composition (by 1H NMR): 99%. Isolated yield: 0.06 g, 55%. 1H NMR (500 MHz, CDCl3): δ 9.00 (s, 2H), 7.35 (d, J = 4.1, 2H), 7.21 (d, J = 4.1, 2H), 4.57 (d, J = 7.4 Hz, 4H), 2.10−2.20 (m, 2H), 1.12−1.40 (m, 64H), 0.86, 0.87 (2 t, J = 7.0 Hz, 12H). 13C NMR (126 MHz, CDCl3): δ 191.9, 160.5, 148.1, 140.8, 140.7, 133.1, 131.3, 128.5, 125.6, 121.1, 120.6, 51.4, 35.4, 31.92, 31.91, 31.6, 30.1, 29.70, 29.66, 29.64, 29.59, 29.36, 29.35, 26.4, 22.69, 22.68, 14.13. LRMS (LDI-TOF) m/z: [M + H] + calcd for C62H88Br2N2O2S2Se2H, 1275.31; found, 1274.91. Anal. Calcd for C62H88Br2N2O2S2Se2: C, 58.40; H, 6.96; N, 2.20. Found: C, 58.63; H, 7.06; N, 2.17. FT-IR (neat, cm−1): 1685 (vCO), 1127 (vCS). Optical absorption (CHCl3): λmax = 489 nm. General Procedure for Post-Polymerization Thionation. PNDIT2 (0.02 g), Lawesson’s reagent (0.04 g, 0.1 mmol), and a stir bar were dried under a vacuum in a sealed microwave vial for 30 min. The reaction vessel was backfilled with argon; dry toluene (1 mL) was added by syringe, and the mixture was briefly sonicated. In a microwave reactor, the mixture was heated up at maximum power (400W; then the temperature was maintained at 180 °C for the designated reaction time (2.5 min for S40-PNDIT2 and 5 min for S60PNDIT2). Toluene was removed in vacuo, and the crude product was redissolved in chloroform (10 mL), sonicated, and precipitated into methanol. The precipitate was washed with boiling methanol overnight and extracted with boiling chloroform (S40-PNDIT2) or chlorobenzene (S60-PNDIT2). Then the solvent was removed in
vacuo to afford a green solid (S40-PNDIT2, S60-PNDIT2). Isolated yield: 0.02 g (S40-PNDIT2, S60-PNDIT2).
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b02162. Parent compound structures and synthetic schemes; supplementary microwave thionation figures; thermogravimetric analysis plots; DFT optimized geometries, HOMO/LUMO visualizations and frequency calculations; and supplementary NMR (1H, 13C, COSY, and HMBC), infrared, optical absorption, and photoluminescence spectra (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Dwight S. Seferos: 0000-0001-8742-8058 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors acknowledge Professor A. Facchetti and Flexterra Inc. for providing the parent polymer N2200 and Professor M. Taylor at the University of Toronto for use of the synthetic microwave. This work was supported by the NSERC of Canada, the Canadian Foundation for Innovation, and the Ontario Research Fund.
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REFERENCES
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