Acenes are a key class of organic molecules for a range of optical and electronic applications. [1][2][3] Pentacene, bis(triisopropylsilylethynyl)pentacene, and rubrene are examples of key benchmarking materials for organic fieldeffect transistors due to their high charge-carrier mobility in either thin films or a single-crystal devices. Their electronic structures also make acenes among the best materials for singlet fission applications in photovoltaics. 4 In addition, cycloaddition reactions, especially between anthracene moieties and reactive dieneophiles such as maleimides, are important ligation reactions for materials. 5,6,7,8 For most applications of long acenes, such cycloadditions can be problematic, as they destroy the conjugation of the acene core and introduce bridgehead linkages. Although acene-alkyne cycloadditions or [4+4] reactions can occur, 9,10 chief among these problematic reactions is photoinduced endoperoxidation of acenes through a reactive oxygen species intermediate such as singlet oxygen or superoxide. 11,12 Typical endoperoxidation mechanisms involve photosensitized formation of either 1 O2, or superoxide oxidation of the acene. 13 In many cases, the acene itself acts as both the sensitizer and diene. 14 Numerous structural modifications have emerged that can reduce the competitiveness of this oxidation. 15 Examples include: i) steric hinderance of the reactive acene core with, [16][17][18] ii) diethynylpentacenes that physically quench 1 O2; 19 iii) other directly attached pendants on pentacene, such as thiol, thioether, or open-shell substituents. 16,20 Re-cently, Briseno and co-workers described thiophene-substituted rubrene analogs with improved resistance to photo-oxidation attributed to rapid non-radiative decay that were unable to sensitize ROS. 21 Finally, Linker identified the reduced barriers to endoperoxide cycloreversion of ethynylated or pyridine-substituted acenes as an approach for recovering acenes after oxidation. 22,23 Acene endoperoxidations have found important application in responsive fluorophores. Dye-anthracene conjugates can undergo fluorescence "turn-on" upon cycloaddition due to elimination of electron transfer quenching. 24,25 The commercially available probe Singlet Oxygen Sensor Green (SOSG) is an example of this approach. Our group has reported materials that contain the more reactive, longer acenes for 1 O2-responsive materials. These materials operate by inhibiting energy transfer from a donor chromophore to acenes, resulting in ratiometric fluorescent responses. 26 We have employed this approach in aqueous samples using conjugated polymer films, 27 acrylic polymers, 28 and conjugated polymer nanoparticles. 29,30 A persistent challenge in 1 O2-responsive fluorophores, however, is the proclivity of many chromophores, to sensitize ROS themselves, increasing background signal. 31 Several probes address this challenge, including the dianionic Aarhus Sensor Green of Ogilby and coworkers, 32 isobenzofuran-based probes that do not produce 1 O2, 33 and chemiluminescent approaches that do not require photoexcitation. 34 These probes generally use slower 1 O2 cycloaddition reactions than are available with longer acenes.
As shown in Scheme S1 (SI), we relied on unsymmetrically substituting the pendant acene (either benzene, naphthalene, or anthracene) with an aryl iodide and a TIPSethynylene by selective Sonogashira coupling of the parabromoiodide followed by lithium-bromide exchange and quenching with I2. The resulting aryl iodides then underwent Sonogashira coupling at elevated temperatures with either diethynyltetracene or diethynylanthradithiophene, each of which was prepared from the corresponding quinones in an addition-reduction-desilylation procedure. All four final compounds were at least moderately soluble; ADT-3 resisted dissolution the most of the four, although it was sufficiently soluble to enable characterization.
Electronic Absorbance Spectrophotometry and Density Functional Theory Figure 1 shows the UV/vis spectra of these molecules in CH2Cl2 at low (10 -5 -10 -6 M) concentration, while Table 1 summarizes their key spectroscopic parameters. These spectra share some common features of diethynylacenes, such as an intense and sharp transition in the UV and broad bands in the visible with some vibronic resolution. As the lengths of the acene pendants increase from benzene through anthracene, the onset of absorbance and lmax of the lowest energy bands in the visible spectrum shifts to lower energy, with anthracene-conjugated TET-3 showing lmax of 590 and 620 nm. In addition, TET-3 and ADT-3 show distinct bands from 360-480 nm that resemble isolated diethynylanthracene chromophores. As dropcast thin films (see Supporting Information), TET-1 and TET-2 show spectra that, while broadened, are consistent with those in solution. In contrast, the solid-state absorbance of both TET-3 and ADT-3 stretch substantially to the red, and in the case of TET-3, display a new intense band at 720 nm. Preliminarily, we attribute this to a combination of increased planarization and intermolecular aggregation. Although attempts to fabricate organic field-effect transistors (OFETs) in a bottom-gate, bottom-contact geometry using TET-3 were successful, 43 the tendency of this molecule to form small needles upon deposition limited observed mobility to ~10 -4 cm 2 /Vs. We calculated the molecular orbitals and optical transitions of these molecules using density functional theory (DFT) and time-dependent DFT with the B3LYP functional and the 6-31G+(d,p) basis set. Geometry optimization at this level of theory shows torsional angles of 32-35° for TET-3 and ADT-3, similar to previously reported molecules with three anthracenes connected through ethynyl linkers. 39 We attribute this twisting to steric interactions between the C-H bonds on acene rings adjacent to the ethynyl linkages-TET-2 (20-24° torsional angles) and TET-1 (0° torsional angles) show improved planarity between arenes. Figure 2 shows the HOMO-2 through LUMO+2 wavefunctions for TET-3. For all four molecules, the lowest energy transition with non-zero oscillator strength is HOMO-LUMO in nature, with the electronic density for each mostly on the central long acenes, with some occupancy along the entire p-conjugated system. As an example, TET-3 shows two key electronic transitions calculated to result from visible light with oscillator strengths f > 0.2: i) 1.72 eV, purely HOMO to LUMO and ii) 2.91 eV, mostly HOMO-1 to LUMO+1, localized on the anthracene units.
We began our investigation of the photochemical oxidation of these acenes by irradiating methylene blue (MB) as an external sensitizer selectively in CH2Cl2 using a 200W Hg/Xe lamp and a 630 nm long-pass filter to irradiate MB in the presence of each acene. We measure the concentration of the acene as a function of irradiation time using UV/vis spectrophotometry. With constant light flux and sensitizer absorbance, we assume a steady-state concentration of 1 O2 while irradiating, and therefore fit the resulting data to a pseudo first-order kinetic model. We also monitored the disappearance of 9,10-diphenylanthracene (DPA) in a separate experiment under identical conditions as an external standard as it resembles the reactive anthracene unit in 1 O2-sensitive fluorophores DPAX and Aarhus Sensor Green. 32,44 Figure 3 summarizes the results of these experiments and analyses, which shows that the four acenes all have similar reactivities with 1 O2. Relative to that of DPA, these acenes react with rate constants (krel) of 4-6. This range is consistent with the reactivity of the previously reported compound from our group, DE-TET (Chart 2) which reacts ~5-times faster than a similar 9,10-diarylanthracene. Therefore, neither the extended arylene-ethynylene linkers nor the conjugated naphthalene or anthracene pendants noticeably impact the intrinsic reactivity of these diethynylacenes with 1 O2. The evolution of the optical spectra of these four acenes as they react are consistent with oxidation of the long central acene moiety, although the tetracenes retain broad absorbance between 400-500 nm. We attribute this feature to retention of the fully conjugated arylene-ethynylene linker when the tetracene is oxidized across the unsubstituted 6 and 11 positions (vide infra). In addition the structured absorbance of TET-3, ADT-3 after oxidation indicates the persistence of the diethynylanthracene side groups. Chart 2. Structure of diethynyltetracene DE-TET.
NMR spectroscopy of TET-3 upon photo-oxidation at higher acene concentration (~ 1 mM) using MB as photosensitizer provides further support for endoperoxide formation (SI). Based on the chemical shifts of the singlets associated with the hydrogen atoms on the unsubstituted 6 and 11 positions of the tetracene, we approximate a 2:1 molar ratio of the 6,11-endoperoxide to the 5,12-endoperoxide; this preference for oxidation at the non-ethynylated position of tetracene agrees with our previous work. 45 Fluorescence Spectroscopy We also determined how the changes in chemical structure influence the fluorescence spectroscopy of these molecules in dilute organic solvent. Our previous work has shown that most 5,12-diethynyltetracenes and analogous diethynylanthradithiophenes have FF = 0.5-0.9 and
lmax(emis) = 575-590 nm; 26,42 additional phenyl substitution on the 6 and 11 positions of tetracenes shifts emission past 600 nm, with FF > 0.6. 46 The maximum wavelength of fluorescence for these four compounds (Figure 4) shifts with increasing conjugation of the arene pendants, from 581 nm for TET-1, 600 nm for TET-2, and greater than 650 nm for both TET-3 and ADT-3. Notably, anthracenecontaining TET-3 and ADT-3 are very weakly fluorescent (FF < 0.003). This observation is consistent with previously reported observations of weak fluorescence from ethynyl-bridged multi-acene structures with either two conjugated tetracenes or three conjugated anthracenes. 46,47 We attribute this quenching to rapid non-radiative decay of the excited states of TET-3 and ADT-3 induced by molecular motions, promoted by the steric hindrance between adjacent acenes in these molecules reflected in the geometry optimized structures. Alternative explanations we considered are inconsistent with experimental observations: intramolecular electron transfer is unlikely due to the paucity of any solvatochromic effect and the lack of donor-acceptor motifs, while intermolecular aggregation in solution is also unlikely as the shape of absorbance spectra in solution do not vary between 40 µM and 2 µM. As shown in Figure 5, TET-1 (582 nm) and TET-2 (601 nm) show ratiometric responses to 1 O2: initial acene fluorescence decreases in intensity as the tetracene oxidizes, while fluorescence from the endoperoxides emerge. In contrast, the very weakly emissive TET-3 shows a "turnon" of fluorescence. Comparing the fluorescence of the three mixtures of oxidized tetracenes, longer pendant arenes yield bathochromically shifted final fluorescence: TET-1 (benzene) at 425 nm, TET-2 (naphthalene) at 452 nm, and TET-3 (anthracene) at 537 nm. We attribute these fluorescence spectra to the tetracenes oxidized across the 6 and 11 positions, which retain a conjugated chromophore along the entire molecule. In contrast, endoperoxidation of ADT-3 is more likely across the central anthradithiophene ring, interrupting conjugation along the arylene-ethynylene chromophore, yielding blue shifted emission (478 nm).
For many applications of acenes, preventing photooxidation of acenes upon direct irradiation is crucial. Highly reactive acenes such as pentacene and rubrene suffer from self-sensitized oxidation, while physical quenching of 1 O2 bestows TIPS-pentacene with slow inherent reactivity. For fluorogenic sensing materials for 1 O2, direct irradiation of the fluorophore is necessary to measure luminescent response; if the fluorophore itself generates 1 O2 or other ROS, false positives can occur. This drawback is a reported characteristic of the commercially available Singlet Oxygen Sensor Green (SOSG). 31,32 Therefore, approaches to preventing "self-sensitization" of ROS while preserving their inherent reactivity is important for improving the performance of responsive fluorophores. We therefore monitored the concentration of these four acenes in CHCl3 in the absence of any external sensitizer, while irradiating them directly at 546 nm (12 mW/cm 2 ); the initial absorbance of all samples was 0.45 at 546 nm. As Figure 6 shows, fluorescent TET-1 and TET-2 degrade rapidly, with half-lives of 8-12 minutes. In contrast, quenched TET-3 and ADT-3 don not degrade after 20 minutes of irradiation. Our previous observation that the rates of reactions with 1 O2 for these four acenes are nearly identical makes it unlikely that physical quenching of 1 O2 by TET-3 or ADT-3 contributes to their persistence during direct irradiation. Instead, consistent with the rapid non-radiative relaxation of their excited states that we infer from FF<0.003, we attribute their persistence 3 to poor photosensitization of ROS. To further support this conclusion, we compared the photosensitization performance of TET-3 and our previously reported, highly fluorescent diethynyltetracene DE-TET in the oxidation of a diaryltetracene probe. As shown in the Supporting Information, irradiation of DE-TET completely oxidized the probe within three minutes, while irradiation of TET-3 under otherwise identical conditions led to only 50% oxidation of the probe after thirty minutes of irradiation. In conclusion, this work describes the synthesis, spectroscopy, reactivity, and fluorescence response to photogenerated 1 O2 of four extended acenes. Our approaches for preparing these compounds are broadly applicable to others investigating multi-acene structures. Even though the aromatic pendant groups did not alter the intrinsic reactivity of these compounds with 1 O2 substantially, the anthracene pendants yield rapid non-radiative decay, which we attribute to steric interactions between the conjugated acenes. TET-3 and ADT-3 are therefore poor sensitizers, dramatically increasing their photochemical stability upon direct irradiation. Given the importance of multiacene structures in a range of applications, we suspect that these connections between structure and reactivity will inform the work of others interested in the fundamental and applied aspects of acenes.
General Information. All synthetic manipulations were performed under standard air-free conditions under an atmosphere of argon gas with magnetic stirring unless otherwise mentioned. Flash chromatography was performed using silica gel (230-400 mesh) as the stationary phase. NMR spectra were acquired on a 500 MHz spectrometer. Chemical shifts are reported relative to residual protonated solvent (7.26 ppm for CHCl3 or 3.58 ppm for THF). High-resolution mass spectra (HRMS) were obtained using different ionization techniques and a peakmatching protocol to determine the mass and error range of the molecular ion. Electronic absorbance spectra were acquired with a spectrophotometer in double-beam mode using a solvent-containing cuvette for background subtraction spectra. Fluorescence spectra were collected at a 90° angle from the incident irradiation (75W Xe lamp) and corrected for both fluctuations in the lamp intensity and the wavelength-dependent sensitivity of the photomultiplier tube detector. Fluorescence quantum yields were determined relative to coumarin 6 in ethanol. 48 Time-resolved fluorescence data were collected using a time-correlated single-photon counting instrument with a pulsed LED operating at 403 nm. Irradiation of methylene blue photosensitizer to generate 1 O2 was performed with a 200 W Hg/Xe lamp equipped with a condensing lens, water filter, and manual shutter, with different long pass filters. Density functional theory calculations were performed using the Gaussian 09 software package 49 , with optimized geometries and FMO energies determined at the B3LYP/6-31G (d,p) level of theory using a polarizable continuum solvent model for CH2Cl2. The time-dependent results of these optimized geometries were calculated with the same functional and basis set, using the Tamm-Dancoff approximation. For fabrication of transistors, highly p-doped silicon was used as the bottom-gate electrode, and 285 nm thermally grown SiO2 served as the gate dielectric. Cr/Au (5 nm/40nm) source and drain electrodes were evaporated through a shadow mask at 0.5 Å/s and functionalized with the self-assembled monolayer (SAM) pentafluorobenzenethiol (PFBT) by vapor deposition at 70 °C for 2 hours. This SAM serves to shift the electrode work function away from the vacuum level, enhancing charge injection in ptype organic semiconductors. 50 To modify the surface energy and allow crystallites to form on the substrate, the silicon oxide layer was functionalized with trichloro(phe-nyl)silane by immersion in a 60 mM solution in chloroform for 1 hour, followed by immersion in fresh chloroform and a thorough rinse with 2-propanol. A 0.25 wt% solution of TET-3 in chlorobenzene was then prepared and devices were formed using solvent-assisted crystallization, 51 where the solution is drop-casted onto the patterned substrate in a covered petri dish with 100 µL chlorobenzene dispensed around the substrate. This technique creates a solvent-rich atmosphere such that the semiconductor solution evaporates more slowly, allowing for the formation of larger crystallites. 52 Electrical measurements were then taken using two Keithley 2400 source-measure units in dark at ambient atmosphere. Synthesis 5,12-bis [2-(trimethylsilyl)ethynyl]tetracene. This reaction was executed following a reported procedure. 53 In a flamedried 2-neck round bottom flask, trimethylsilylacetylene (0.71 mL, 490 mg, 5.0 mmol) was dissolved in 20 mL of dry diethyl ether and cooled to 0°C in an ice-water bath. n-Butyllithium (2.2 mL, 4.8 mmol, 2.2 M in hexanes) was added dropwise. The colorless solution was allowed to warm to room temperature and stirred for 1 h, at which time napthacenequinone (520 mg, 2.0 mmol) was added as a solid. The suspension was stirred overnight and then neutralized with 1 M HCl (aq) and SnCl2•2H2O (1.0 g, 4.4 mmol) was added to the mixture. After stirring for 3 h, the mixture was extracted using CH2Cl2 (3 x 10 mL), and the combined organic layers were dried over MgSO4. The solvent was removed in vacuo, and the residue was purified through a plug of silica, eluted with hexanes to give 540 mg of the expected product ((65% yield) as a deep red powder . 1 H NMR (500 MHz CDCl3): δ 9.20(s, 2H) 8.57-8.59 (dd , 2H), 8.08-8.10 (dd, 2H), 7.55-7.60 (dd, 2H), 7.47-7.49 (dd, 2 H), 0.54 (s, 18H). The chemical shifts are consistent with those reported in the literature. 53 5,12-diethynyltetracene.
5,12-bis[2-(trimethylsilyl) ethynyl]tetracene (210 mg, 0.50 mmol) was dissolved in 10 mL CH2Cl2/methanol (1:1, v/v). To the solution, potassium carbonate (210 mg, 1.5 mmol) was added. The suspension was stirred at room temperature for 4 h. The solvent was removed, and the residue was extracted with CH2Cl2 (3 x 10 mL). The combined organic phase was sequentially washed with water and brine, and dried over MgSO4. In syntheses of TET-1, TET-2, and TET-3, the crude product was used immediately after removing the solvent.
Triisopropylsilylacetylene (0.22 mL, 180 mg, 1.0 mmol) of triisopropylsilyl acetylene was dissolved in 30 mL THF/triethylamine (2:1 v/v). The solution was deoxygenated with argon gas for 1 h. To another flame-dried twoneck round bottom flask, 1-iodo-4-bromobenzene (283 mg 1.0 mmol), bis(triphenylphosphine)palladium(II) dichloride (35 mg, 0.05 mmol), and copper (I) iodide (10 mg, 0.05 mmol) was added. Then, the degassed solution was transferred to the flask containing solids via cannula. The mixture was stirred overnight at room temperature. The solvent was removed in vacuo. The resultant solid was purified by flash column chromatography (hexanes) to yield the desired product as a colorless oil (320 mg, 95% yield). 1 H NMR (500 MHz CDCl3): δ 7.42-7.44 (d, 2 H), 7.32-7.34 (d, 2 H), 1.09-1.12 (m, 21 H), The resonances are consistent with those reported previously in the literature. 54 1-iodo-4-(2-triisopropyl)ethynyl-benzene. In a flame-dried two-neck round bottom flask, 1-bromo-4-(2-triisopropyl)ethynyl-benzene (870 mg, 2.6 mmol) was dissolved in 10 mL of dry diethyl ether. n-butyllithium (1.14 mL, 2.8 mmol, 2.5 M in hexanes) was added dropwise after cooling the solution to -78 °C. The solution was stirred at -78 °C for 1 h. I2 was added as a solid (857 mg, 3.4 mmol) and the mixture was allowed to warm up to ambient temperature. The reaction was then stirred for 8 h followed by quenching with 10 mL saturated ammonium chloride solution. The mixture was then extracted with CH2Cl2 and dried over MgSO4. The crude product (870 mg, 87% yield) was directly used after removing the solvent without any further purification.
(TET-1). In a round bottom flask, 1-iodo-4-(2-triisopropyl)ethynyl-benzene (670 mg, 1.7 mmol) was dissolved in 9 mL toluene/diisopropylamine (2:1 v/v). The solution was deoxygenaged by bubbling with argon for 1 h. To another flame dried two-neck round bottom flask equipped with a condenser, 5,12-diethynyltetracene (180 mg, 0.63 mmol), Cl2Pd(PPh3)2 (30 mg, 0.04 mmol), and CuI (10 mg, 0.05 mmol) was added. The degassed solution was then transferred to the flask via a syringe. The mixture was then stirred at 80 °C in an oil bath for 36 h. The solvent was removed in vacuo, and the residue was purified via flash column chromatography (CH2Cl2/hexanes 1:1 v/v). The crude product was recrystallized from CHCl3/MeOH to yield TET-1 (150 mg, 30% yield) as a purple solid.
A flamedried round bottom flask was charged with 1-iodo-4-bromonaphthalene (1.2 g, 3.7 mmol) and 30 mL of degassed THF/NEt3 (2:1 v/v). Pd(PPh3)2Cl2 (100 mg, 0.14 mmol) and CuI (0.2 mmol, 40 mg) was added to the solution. With a syringe, triisopropylsilylacetylene (0.82 mL, 3.7 mmol) was added to the solution. The reaction was stirred overnight before purification by elution through a plug of silica with hexanes. After removing the solvent under vacuum, 1.25 g of the desired product was obtained as a pale-yellow oil. (88% yield).
In a flame dried round bottom flask, 1-bromo-4-(2-triisopropyl)ethynyl-naphthalene (1.25 g, 3.3 mmol) was dissolved in 10 mL of dry THF. The solution was cooled to -78 °C using an acetone/dry ice bath. With a syringe, n-butylithium solution (2.0 mL, 5.0 mmol, 2.5 M in hexanes) was added dropwise. The solution was stirred at -78 °C for 1 h, and then I2 (1.5 g, 6 mmol) was added as a solid. The reaction was stirred overnight, and then quenched with aqueous NaS2O3. The mixture was extracted with CH2Cl2 three times, and the combined organic layers were dried over MgSO4. Then, the solvent was removed in vacuo to yield 1.38 g yellow oil. This crude product was directly used in the next step without further purification (96% yield).
. A round bottom flask was charged with a solution of 1-iodo-4-(2-triisopropyl)ethynyl-naphthalene (1.0 g, 2.3 mmol) dissolved in 14 mL of a toluene/diisopropylamine (4:3 v/v) mixture. The solution was then deoxygenated by bubbling with argon for 1 h. This solution was transferred by cannula into a flamed dried round bottom flask containing compound 8 (280 mg, 1.0 mmol), Pd(PPh3)2Cl2 (35 mg, 0.05 mmol), and CuI (10 mg, 0.05 mmol). The reaction was heated to 80 °C in an oil bath and stirred for 20 h. The mixture was first purified by flash column chromatography (gradient elution 1:4 CH2Cl2/hexane to 100% CH2Cl2). Finally, 530 mg of pure TET-2 was isolated by recrystallization from chloroform/methanol as a purple solid (60% yield).
9-iodo-10-bromo-anthracene. In a flame-dried round bottom flask, 9,10-dibromoanthracene (1.0 g, 3.0 mmol) was added to 30 mL of dry THF and cooled to -78 °C. To the suspension, n-butyllithium (1.3 mL, 3.3 mmol, 2.5 M in hexanes) was added dropwise. The resulting solution was allowed to warm to room temperature and stirred for another 3 hours. The flask was cooled to -78°C again followed by the addition of 1.0 g of I2 (3.9 mmol). After stirring at room temperature for 20 h, the solution was concentrated in vacuo to approximately 10% of its original volume. Sodium thiosulfate aqueous solution (20 mL, 20% w/v) was mixed into the residue, and the resulting precip-itate was collected by vacuum filtration to afford the desired product as needle-shaped yellow crystals (1.04 g, 91% yield) 1 H NMR (500 MHz CDCl3): δ 8.56-8.58 (m, 4 H), 7.61-7.63 (m, 4H). The chemical shifts are consistent with those reported previously in the literature. 55 9-bromo-10-(2-triisopropyl)ethynyl-anthracene. A flamedried round bottom flask was charged with a solution of 9-iodo-10-bromo-anthracene (1.04 g, 2.7 mmol) dissolved in 30 mL of a degassed THF/ NEt3 (2:1, v/v) mixture. Pd(PPh3)2Cl2 (98 mg, 0.14 mmol) and CuI (26 mg, 0.14 mmol) were added to the solution. With a syringe, triisopropylsilyl acetylene (0.61 mL, 2.7 mmol) was added to the solution. The mixture was stirred overnight at ambient temperature. The solvent was then removed in vacuo and the residue was purified by flash column chromatography (hexanes) to afford 1.10 g of the desired product as a pale yellow oil (93% yield). 1 H NMR (500 MHz CDCl3): δ 8.54-8.68 (m, 4H), 7.60-7.64 (m, 4H), 1. 25-1.30 (m, 21 H). The resonances are consistent with those reported previously. 56 9-iodo-10-(2-triisopropyl)ethynyl-anthracene. In a flamedried round bottom flask, 9-bromo-10-(2-triisopropyl)ethynyl-anthracene (600 mg, 1.4 mmol) was dissolved in 10 mL of dry diethyl ether. The solution was then cooled to -78°C. n-butyllithium (1.1 mL, 2.1 mmol, 2.2 M in hexanes) was added dropwise to the solution. The mixture was stirred for 1 h at -78°C, after which solid I2 (630 mg, 2.5 mmol) was added to the mixture, and the reaction was allowed to warm to room temperature and stirred overnight. After quenching by adding sodium thiosulfate aqueous solution (20% w/v), the mixture was extracted with diethyl ether three times. The combined organic layers were dried over MgSO4 and the solvent was removed under vacuum to afford the desired product as a red oil, (626 mg, 93% yield) which was used for the next step without further purification.
)ethynyl]tetracene (TET-3). A round bottom flask was charged with 9-iodo-10-(2-triisopropyl)ethynyl-anthracene (490 mg, 1.0 mmol) dissolved in 5 mL of a toluene/diisopropylamine mixture (3:2 v/v). The solution was then deoxygenated by bubbling with argon for 1 h. To a flame-dried round bottom flask, compound 8 (130 mg, 0.5 mmol), Pd(PPh3)2Cl2 (14 mg, 0.02 mmol) and CuI (10 mg, 0.05 mmol) were added as solids. The degassed solution was transferred into the flask containing solids using a cannula.. After stirring in the dark for 24 hours at 80 °C in an oil bath, the solvent was removed in vacuo. The residue was passed through a plug of silica with CH2Cl2 to remove highly polar impurities. The product was then recrystallized from acetone to yield 140 mg of TET-3 as a blue solid (28% yield).
Anthradithiophene-5,11-dione.
1,4-cyclohexanedione (0.84 g, 7.5 mmol) was added to a solution of 2,3-thiophene dicarbaldehyde (2.1 g, 15 mmol) in 100 mL ethanol. 6 mL of 15% (w/v) KOH aqueous solution was then added dropwise. The reaction was stirred at ambient temperature for four hours. The resulting precipitate was collected by vacuum filtration and washed with ethanol to obtain the product as a yellow solid. (2.4 g, 99% yield), which was used directly without any purification. 5,11-bis[2-(trimethylsilyl)ethynyl]-anthradithiophene. In a flame-dried round bottom flask, triisopropylsilylacetylene (1.1 mL, 5.0 mmol) was dissolved in 20 mL of dry diethyl ether and cooled to 0 °C. A solution of n-BuLi (5 mmol, 2.0 mL 2.5 M in hexanes) was added dropwise. The mixture was stirred at 0 °C for 30 minutes and stirred at room temperature for another hour. Then, anthradithiophene-5,11-dione (640 mg, 2.0 mmol) was added as a solid. The reaction was stirred at room temperature overnight. The pH of the reaction was tuned to approximately 7 using a 0.1 M HCl aqueous solution, and then 1.0 g of SnCl2•2H2O was added to the mixture. This mixture was stirred in the dark for 3 hours. The mixture was extracted with diethyl ether 3 times and the combined organic phases were dried over MgSO4. The crude product was purified using column chromatography (hexanes) to obtain the desired product (850 mg, 60% yield). ), These resonances are consistent with those reported in the literature. 10 5,11-diethynylanthradithiophene. In a round bottom flask, 5,11-bis[2-(trimethylsilyl)ethynyl]-anthradithiophene (130 mg 0.20 mmol) was dissolved in 5 mL of THF and cooled to -78 °C. 2.0 mL of TBAF solution (1 M in THF) was added dropwise. In the dark, the reaction was stirred for 5 min at -78 °C and stirred for another hour at room temperature. After quenching the reaction with 10 mL of water, the precipitate was filtered and washed with water and cold methanol to afford the desired product as a red solid. (340 mg, 83% yield) 1 H NMR (300 MHz CDCl3): δ = 9.19 (s, 2H), 9.12 (s, 2H), 7.56-7.58 (d, 2H), 7.48-7.49 (d, 2H). 4.24-4.29 (m, 2H). The solubility of this compound is very low in solvents for NMR spectroscopy. Thus, the 13 C NMR spectrum could not be obtained with high quality. 5,11-Bis[((10-triisopropylethynyl)anthracenyl)ethynyl]anthradithiophene (ADT-3). In a round bottom flask, 9-iodo-10-(2-triisopropyl)ethynyl-anthracene (1.20 g, 2.5 mmol) was dissolved in 15 mL of THF/diisopropylamine (2:1 v/v). The solution was then deoxygenated by bubbling with argon gas for 1 h. In another flame-dried flask, of 5,11-diethynylanthradithiophene (340 mg, 1.0 mmol), Pd(PPh3)2Cl2 (35 mg, 0.05 mmol), and CuI (10 mg, 0.05 mmol) were added as solids. The degassed solution was then added to the flask with solids using a cannula. The reaction was stirred at 80 °C in an oil bath for 24 hours. After removal of solvent in vacuo, the residue was passed through a plug of silica with CH2Cl2 eluent. The product was recrystallized from acetone twice and then chloroform/methanol twice to yield ADT-3 as a dark green solid. (250 mg, 25% yield). 1 H NMR (500 MHz THF-d8): δ 9.00-9.07 (m, 4H), 8.73-8.74 (m, 4H), 8.58-8.60 (m, 4H), 7.60 (m, 2H), 7.56 (m, 4H), 7.25 (m, 4 H), 6.92 (m, 2 H), 1.38-1.4 (m, 42 H). HRMS (MALDI matrix: DCTB): m/z calcd for C72H66S2Si2 (M + ) 1050.4144, found 1050.4104. The product is a mixture of slightly soluble trans-/cis-isomers, so the multiplicity of signals cannot be distinguished. However, the structure can be confirmed by the HRMS and 2D-NMR. In addition, the solubility of ADT-3 is very low in solvents for NMR spectroscopy. Thus, the 13 C NMR spectrum cannot be obtained with high quality.