Acceptor in Push-Pull Dyes - ACS Publications

Article pubs.acs.org/joc

Cite This: J. Org. Chem. 2017, 82, 11008-11020

Pulling with the Pentafluorosulfanyl Acceptor in Push−Pull Dyes Prabhat Gautam, Craig P. Yu, Guoxian Zhang, Victoria E. Hillier, and Julian M. W. Chan* Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie Pvt. Ottawa, Ontario K1N 6N5, Canada S Supporting Information *

ABSTRACT: A new class of push−pull fluorophores featuring the pentafluorosulfanyl (SF5) group as a potent acceptor has been synthesized. Known for its excellent chemical and thermal stability, the unique SF5 functionality is also strongly electron-withdrawing but at the same time highly lipophilic. We report six new fluorescent dyes, which were characterized by UV−vis/fluorescence spectroscopy, single-crystal X-ray diffraction, and cyclic voltammetry. Notable dye properties include large Stokes shifts (>100 nm), pronounced solvatofluorochromic effects arising from intramolecular charge transfer, moderate fluorescence quantum yields in both solutions and thin films, and extensive supramolecular C−H···F interactions in their crystalline states. Reversible mechanofluorochromism was also observed in dye 5, where grinding and fuming of a solid sample gave blue- and red-shifted emissions, respectively. Postfunctionalization of dye 3 to afford a pair of strong visible-light absorbers was also demonstrated.

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INTRODUCTION The design and synthesis of novel push−pull molecules composed of electron donors (D) and acceptors (A) bridged by π-linkers (i.e., D−π−A) has been of considerable interest due to their wide-ranging applications in biological imaging, biosensing, organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), mechanofluorochromic materials, and nonlinear optics.1−4 Ideally, D−π−A systems designed for these applications should have high molar absorption coefficients, high fluorescence quantum yields, large Stokes shifts, and good photostability. The modular nature of D−π−A dyes allows for fine-tuning of their physical properties through rational modification of each component.5 In this study, we were interested in using the unique pentafluorosulfanyl (SF5) functional group6 as a powerful electron acceptor in such push−pull systems (Figure 1). First discovered by Sheppard et al. over 50 years ago,7 the SF5 moiety remained little explored in subsequent decades mainly due to its inconvenient synthesis and the lack of

commercially available reagents containing the functional group. In recent years, however, the situation has changed, and many SF5-containing molecular building blocks are now available from multiple commercial sources. This has primarily been driven by discovery efforts in the pharmaceutical and agrochemical industries, where new or underexplored functional groups are being investigated for their unique structure− property relationships.6 The SF5 substituent features hypervalent sulfur in an octahedral environment, bonded to one axial and four equatorial fluorine atoms.8 The functional group exhibits high electronegativity, steric bulk, low surface energy, marked lipophilicity, and excellent chemical and thermal stability.9 This has led to the SF5 group being dubbed “super CF3” in the context of drug design and as a “substituent of the future”.8a,10 Outside of medicinal chemistry and agrochemicals research, the substituent has only been featured sporadically in materials chemistry.11 Given its unique properties, the SF5 group holds as much potential in organic materials design as it does in drug discovery. In the area of materials chemistry, the SF5 group has previously been explored by Kirsch and Hahn in the context of designing highly polar calamitic liquid crystal molecules.12 In their work, Kirsch and Hahn synthesized several linear liquid crystalline molecules using Pd-catalyzed cross-coupling reactions (e.g., Suzuki, Sonogashira), in which the SF5 group was unaffected by the reaction conditions employed. Subsequent work by Laali et al. likewise demonstrated the utility of various Pd-catalyzed cross-coupling methodologies in constructing SF5containing molecules,13 albeit outside the context of functional materials research.

Figure 1. Schematic representation of D−π−A push−pull dyes featuring DPA donors and SF5 acceptors. © 2017 American Chemical Society

Received: August 5, 2017 Published: September 25, 2017 11008

DOI: 10.1021/acs.joc.7b01972 J. Org. Chem. 2017, 82, 11008−11020

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The Journal of Organic Chemistry Scheme 1. Synthesis of SF5-Containing D−π−A Fluorescent Dyes 1−3

Scheme 2. Synthesis of SF5-Containing Fluorescent Dyes 4−6 Featuring Extended π-Conjugation

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The Journal of Organic Chemistry Scheme 3. Postfunctionalization of Push−Pull Dye 3 with TCNE and TCNQ

Following the synthesis of donor−acceptor dyes 1−6, we also investigated the postfunctionalization of 3 with tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) using a tandem [2 + 2] cycloaddition/4π electrocyclic ringopening sequence (Scheme 3).20 Reaction of compound 3 with TCNE in dichloromethane at 40 °C for 24 h afforded compound 7 in 80% yield. The analogous reaction of 3 with TCNQ in refluxing chloroform was much slower and the starting materials were not completely consumed even after 64 h. Nonetheless, pure 8 could still be obtained in 30% isolated yield following workup and column chromatography. All eight new compounds 1−8 were readily soluble in common organic solvents such as chloroform, dichloromethane, toluene, tetrahydrofuran, acetone, etc. The compounds were characterized by 1H, 13C, and 19F NMR and high-resolution mass spectrometry (HRMS). Fluorescent dyes 1−6 were also characterized by single-crystal X-ray diffraction studies. Single-Crystal X-ray Analysis. High-quality single crystals of the push−pull dyes 1−4 and 6 were grown by slow diffusion of ethanol in chloroform at room temperature. With dye 5, single crystals were obtained as above, but with ethanol being replaced by acetonitrile. Single-crystal structures were successfully elucidated for all six dyes (Figure 2). Molecules 1−3 crystallized in the monoclinic space group C2/c, 4 and 5 in the monoclinic space group Cc, and 6 in the triclinic space group P-

For our part, we were interested in harnessing the strongly electron-withdrawing effect of the SF5 group in D−π−A push− pull dyes. The electronegativity of the SF5 group is 3.65, which is greater than that of CF3 (3.36), and enables a strong push− pull effect to be set up when conjugated to appropriate electron donors. The strong inductive effect is also evident from the relative dipole moments of pentafluorosulfanylbenzene (μ = 3.44 D) and benzotrifluoride (μ = 2.60 D).14 In terms of steric volume the SF5 group is comparable to a tert-butyl group,9e making it a useful handle for enhancing solubility and materials processability, and may also help reduce aggregation-caused quenching in some cases. In this work, we employed the diphenylamino- (DPA) unit as the donor, a motif that has been used in various push−pull π-systems.15−17 The DPA unit was conjugated to the SF5 acceptor through a variety of bridging πlinkers. Here, we report the synthesis of several DPA−π−SF5 dyes (1−6), their photophysical properties, and how systematic modification of the π-linkers could be used to tune those properties. Using dye 3, we also showed that postfunctionalization by tandem [2 + 2] cycloaddition/4π-electrocyclic ringopening was feasible in the presence of SF5 to afford new molecules 7 and 8 with enhanced charge transfer (CT) bands. In addition to photophysical characterizations, single-crystal Xray diffraction, electrochemical, and theoretical studies were also performed, and the results are reported herein.

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RESULTS AND DISCUSSION Synthesis. The versatile and commercially available 4bromo(pentafluorosulfanyl)benzene 9 was used as the common precursor to all six of our push−pull fluorescent dyes 1−6 (Schemes 1 and 2). Dyes 1−3 featured short π-linkers and were synthesized by Pd-catalyzed cross-coupling reactions between 9 and appropriately functionalized building blocks (10−12) containing the diphenylamino donor group (Scheme 1).18 Isolated yields from the Suzuki, Heck, and Sonogashira couplings were moderately high, and purification by column chromatography was exceptionally facile due to the solubilizing effect of the SF5 group as well as its lipophilic nonpolar nature. Dyes 4−6 featured extended π-conjugated bridges between the SF5 acceptor and the diphenylamino donor. Their syntheses similarly involved Pd-catalyzed cross-couplings between 9 and premade building blocks (13−15) prepared using previously published procedures (Scheme 2).19 Once again, the isolated yields were generally high (70−80%), and reactions proceeded without any apparent incompatibilities between the chosen conditions and the SF5 group.

Figure 2. Structures of 1−6 as determined by single-crystal X-ray diffraction analysis. 11010


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The Journal of Organic Chemistry

Figure 3. Crystal packing diagrams of push−pull dyes 1−6.

Table 1. Photophysical Properties of Compounds 1−6 photophysical data compd

solvent

λabs (nm)

λem (nm)

Stokes shift (nm)

ε (10 L·mol−1·cm−1)

ΦF

1

toluene DCM acetone toluene DCM acetone toluene DCM acetone toluene DCM acetone toluene DCM acetone toluene DCM acetone

349 347 344 385 386 381 369 368 363 379 380 373 407 403 397 396 395 387

418 449 461 448 488 500 424 460 488 434 492 515 472 528 547 454 506 531

69 102 117 63 102 119 55 92 125 55 112 142 65 125 150 58 111 144

6.2 5.3 4.9 5.9 5.7 4.2 6.0 4.2 3.4 9.9 9.6 5.1 10.1 9.9 5.0 3.8 2.1 1.9

0.48 0.016 0.010 0.24 0.20 0.070 0.48 0.070 0.010 0.49 0.40 0.15 0.29 0.23 0.19 0.37 0.30 0.17

2

3

4

5

6

4

τa (ns)

λemthin‑film (nm)/ΦFb

λemsolid (nm)

0.33

425/0.24

417

3.12

1.36

467/0.36

481

2.82

2.12

444/0.43

471

2.97

2.07

455/0.60

488

2.87

2.18

487/0.38

563

2.64

1.93

478/0.10

496

2.73

Eg

opticalc

(eV)

Measured in dichloromethane (DCM). bQY in PMMA films were determined using 9,10-diphenylanthracene as a standard (ΦF = 0.83). cOptical gap, Egoptical = 1240/λonset abs. a

1. Packing structures of 1−6 revealed a multitude of intermolecular interactions throughout the crystal lattice. In addition to regular C−H···π interactions, numerous shortcontact C−H···F interactions (2.45−2.65 Å) were observed between molecules. The latter interactions are particularly prolific in SF5-containing organic crystals, as shown in a recent study by Woollins et al.8a For dye 1, its packing diagram revealed intermolecular C− H···π interactions (Figure 3a) that result in the formation of

dimeric molecular pairs held in antiparallel arrangements. Within each pair, the two bulky SF5 groups were projected away from each other, facilitating interdimer H-bonding interactions C(15)−H(15)···F(5) (2.517 Å) that produce a zigzag arrangement along the a-axis. Dyes 2 and 3 (Figures 3b,c) displayed similar patterns, with antialigned dimers held by mutual intermolecular C−H···π interactions between triarylamine moieties. These dimers were in turn connected to neighboring dimers via intermolecular H-bonding interactions 11011


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Figure 4. Normalized absorption and fluorescence spectra of 1−6 as measured in dichloromethane.

showed π-stacked dye pairs interacting intermolecularly via multiple short-contact C−H···F bonds. In 4, extensive SF5mediated H-bonding interactions, i.e., C(18)−H(18)···F(7) (2.637 Å) and C(18)−H(18)···F(10) (2.637 Å), gave dimers that were further held by C(28)−H(28)···F(8) (2.506 Å) and C(6)−H(6)···F(2) (2.647 Å) interactions to form a layered structure. In the case of 5, dimers held by C(59)−H(59)···F(1) (2.655 Å) and C(52)−H(52)···F(5) (2.455 Å) H-bonding

mediated by SF5 groups (i.e., C(23)−H(23)···F(4) (2.655 Å) in 2 and C(10)−H(10)···F(3) (2.628 Å) in 3) to form pseudo2D networks. With dye 3, further extension via additional C(23)−H(23)···F(1) (2.582 Å) H-bonding interactions gave a sheet-like structure along the b-axis (Figure 3c). Dyes 4−6 featuring extended π-systems exhibited even greater intermolecular C−H···F interactions in the crystals, at the expense of C−H···π bonds. Packing diagrams of 4 and 5 11012


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increased even further by replacing DCM with a more polar solvent, e.g., between 117−150 nm in acetone (Table 1). Solvatofluorochromism. The emission colors of the dyes were observed to vary greatly with increasing solvent polarity, and thus, additional spectroscopic experiments were carried out to quantify this solvatofluorochromic effect. The absorption and emission spectra of 1−6 were initially acquired in three different solvents (toluene, DCM, and acetone) for comparison, along with their fluorescence quantum yields. As shown in Figure S7, the absorption profiles of the dyes did not show much dependency on solvent polarity; however, their peak emissions were significantly affected. Large bathochromic shifts in emission maxima (Figure 6) and attenuation of quantum yields were observed with all six dyes when solvent polarity was increased. Such solvatofluorochromic behavior is typically seen in push−pull fluorophores with large excited-state dipole moments that can interact with surrounding solvent molecules, which attests to the potent acceptor strength of SF5 in these dyes.22 This ability to respond to polarity changes is another property of environment-sensitive dyes that finds utility in bioimaging applications.1a To study the solvatofluorochromic effect further, we subsequently measured the emission spectra of dyes 1−6 in three additional solvents (dioxane, chloroform, and acetonitrile) and plotted the emission energies (in cm−1) of the wavelength maxima in all six solvents vs the solvent polarity parameter ET(30) (in kcal/mol). For each dye, a linear correlation was observed, showing the decrease in its emission energy with increasing solvent polarity (Figure S9). Along with the observed red shifts in emission wavelengths, the use of higher polarity solvents also led to decreased fluorescence quantum yields. This observation was especially pronounced in dye 1, which contains a biphenyl linker. Such behavior is well documented in push−pull biphenyls and may be attributed to twisted intramolecular charge transfer (TICT) effects.23 Solid-State Emission Studies and Mechanofluorochromism in 5. The push−pull dyes 1−6 were also emissive in the solid state. The emission maxima measured for the solid samples of 1−6 were observed at 417, 481, 471, 488, 563, and 496 nm, respectively (Figure 7a). Compared to the fluorescence wavelengths in nonpolar solutions (i.e., toluene), the solid-state emissions were all bathochromically shifted except for dye 1. The red shifts are especially large for dyes 4 and 5 (54 and 91 nm, respectively), both of which show extensive aggregation via π−π stacking interactions in the solid state (Figure 3d,e). On the other hand, dye 1 with its less planar biphenyl-type structure, does not display similar cofacial π-stacking in the solid-state (Figure 3a). The emission maxima of 1 in both nonpolar solution and in the solid are 417 nm. With dyes 2, 3, and 6, the red shift in emission wavelengths going from solution phase to solid-state are in the intermediate range, measuring between 33−47 nm. Out of the six dyes, only compound 5 was found to exhibit a mechanofluorochromic effect that is visible to the naked eye, whereby mechanical grinding led to a change in its emission color. Solid-state fluorescence measurements showed that pristine crystals of 5 emitted orange light with a λmax of 567 nm (Figure 7b). Upon being ground to a fine powder, the emission of solid 5 was hypsochromically shifted to yellow, i.e., with an emission peak at 545 nm, corresponding to a blue shift of 22 nm. The blue-shifting of emission upon grinding was likely due to the disruption of molecular packing and aggregation in the crystals in response to the input of

interactions were mutually linked via more short-contact C− H···F bonds to form a layered structure comprised of parallel chains of dye molecules. Finally, while the bent-shape of the thiophene-containing 6 precluded the formation of sheetlike structures, the nature of intermolecular interactions remained similar. The packing diagram of 6 showed the presence of extensive C−H···F bridging interactions between the SF5 and triarylamine moieties of neighboring molecules (Figure 3f). All crystal-state noncovalent interactions of 1−6 are summarized in Table S7. Photophysical Properties. To characterize the photophysical properties of push−pull dyes 1−6, we carried out UV− vis and fluorescence spectroscopy studies in solution phase and in the solid-state (full data summarized in Table 1). The UV− vis absorption and emission behavior of dyes 1−6 were first investigated in dichloromethane (DCM) at room temperature. The normalized absorption and emission spectra of the dyes are shown in Figure 4. In dilute DCM solution, the emissions from all six dyes ranged from blue to yellow-green, and large Stokes shifts were observed in all cases (Figure 4). In general, the molar extinction coefficients of the extended dyes 4 and 5, and the fluorescence quantum yields of 4−6 in DCM were much larger than the shorter analogues 1−3. The molar absorptivities (ε, M−1 cm−1) of the dyes are given in Figure 5 for comparison.

Figure 5. Molar absorptivities (ε) of dyes 1−6 as measured in dichloromethane.

The absorption and emission profiles of 4−6 were also bathochromically shifted with respect to that of 1−3, as would be expected of push−pull systems with extended conjugation lengths. The use of vinylene linkers in molecules 2 and 5 resulted in smaller torsional angles (12.77° and 8.37°, respectively) between the donor- and acceptor-bearing rings compared to dye 1 (37.40°), leading to enhanced π-conjugation (between Ph 2 N donor and SF 5 acceptor) and more pronounced red shifts. More significantly, all six dyes exhibited very large Stokes shift in DCM, ranging from 92 to 125 nm. Fluorophores with large Stokes shifts (i.e., ≥ 80 nm) are of considerable interest for bioimaging applications, as the lack of overlap between the excitation source and dye emission profiles minimizes interference/cross-talk in cellular imaging.21 In general, the Stokes shift values for the vinylene-linked dyes 2 and 5 were comparatively larger than that of the ethynylenebridged dyes 3 and 4. The Stokes shifts of dyes 1−6 could be 11013


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Figure 6. Effect of increasing solvent polarity on the emission wavelengths of dyes 1−6.

mechanical energy.3,24 In particular, since the single-crystal structure of 5 (Figure 3e) shows extensive aggregation through π−π stacking interactions (which cause red shifting), it is likely that the disruption of this ordered state by grinding is the cause of the blue-shifted fluorescence of the ground solid. In order to investigate this, powder X-ray diffraction (PXRD) analysis of pristine and finely ground 5 was carried out. The PXRD pattern of the pristine solid showed sharp and intense reflection peaks (Figure S13), whereas the peaks disappeared almost completely upon mechanical grinding, indicating a morphological transition between the crystalline (ordered) and amorphous (disordered) phases. The mechanofluorochromic behavior of 5 was found to be reversible, in that the fluorescence emission

of 5 could be restored to its original color by fuming with dichloromethane vapor for 1 h. The grinding/fuming procedure was repeated over several cycles, during which the spectroscopic reversibility of 5 could be observed (Figure S12). Mechanofluorochromic molecular systems represent yet another class of stimuli-responsive materials that are currently of interest due to their potential application as deformation detectors, mechanical sensors, memory devices, and security systems.25 Aside from 5, the other five dyes did not display any appreciable mechanofluorochromic effects; i.e., the differences in emission maxima of pristine and ground solids were negligible, i.e., Δλ ∼0−4 nm. 11014


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Figure 7. (a) Solid-state emission of dyes 1−6. (b) Mechanofluorochromism in 5: blue-shifted emission of solid before and after grinding. Inset: photographs of crystalline (left) and ground (right) samples of 5 under UV light (365 nm).

Figure 8. UV−vis absorbance spectra of 3, 7, and 8 as measured in dichloromethane.

Thin-Film Studies. The photophysical properties of dyes 1−6 were investigated in solution-processed thin films of poly(methyl methacrylate) (PMMA), prepared by spin-coating chloroform solutions of each dye codissolved with PMMA. The photoluminescence quantum yields of the dyes in PMMA matrix were determined using a relative method that is well described in the literature.26 The spectroscopic data are summarized in Table 1, and normalized absorption/emission spectra of the films are given in Figure S14. The thin film absorption and emission spectra were generally similar to those acquired in nonpolar solutions. The observed emission wavelengths and Stokes shifts (between 74−86 nm) of dyes 1−6 in the relatively nonpolar PMMA matrix were generally indicative of a local dielectric that is intermediate between that of toluene and dichloromethane. Absorption Properties of Postfunctionalized Molecules 7 and 8. As previously outlined in Scheme 3, the push− pull dye 3 underwent postfunctionalization reactions to afford new molecules 7 and 8. These two nonfluorescent compounds were found to be strongly absorbing chromophores exhibiting intense ICT bands and further red-shifts of their λabs maxima relative to 1−6 (Figure 8). This may be attributed to the highly

electron-accepting nature of the tetracyanated moieties that further augment the SF5 acceptor.20 These intensely colored derivatives of 3 absorb strongly across the visible spectrum and may be potentially interesting for future studies in the field of organic photovoltaic materials. Electrochemistry. The electrochemical properties of 1−8 were studied using cyclic voltammetry (CV). All measurements were performed at room temperature using anhydrous DCM as solvent and tetra-n-butylammonium hexafluorophosphate (Bu4NPF6) as the supporting electrolyte. The electrochemical data are compiled in Table S9, and the cyclic voltammograms are shown in Figure S15. Dyes 1−6 underwent oxidation in the range of 0.71−0.84 V due to the presence of triarylamine donor unit.27 The EHOMO values for 1−8 were calculated from the onset of oxidation, while ELUMO values were calculated using the equation ELUMO = (EHOMO + Egoptical) eV.28 The results show greater stabilization of the LUMO levels in vinylenelinked 2 and 5 as compared to ethynylene-linked 3 and 4, respectively. Incorporating TCNE and TCNQ groups into the postfunctionalized 7 and 8 led to further stabilization of the LUMO relative to that of their precursor 3. These results indicate that the HOMO/LUMO of these systems can be 11015


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Figure 9. Frontier molecular orbitals of dyes 1−6, calculated using Gaussian09 at the B3LYP/6-31G** level for C, N, S, and H.

readily tuned by judicious choice of π-linker bridges and/or by postfunctionalization of those linkers. Density Functional Theory Calculations. To complement the photophysical and electrochemical studies, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were also performed on the SF5-functionalized fluorescent dyes 1−6. The geometries of all six molecules were first optimized, and their frontier molecular orbitals were subsequently calculated. The HOMO coefficients were mainly localized around the triarylamine donor moiety, while the LUMO coefficients were concentrated in the region proximal to the SF5 acceptor (Figure 9). The TD-DFT calculations showed that the lower energy absorption bands in the UV−vis spectrum of dyes 1−6 involved preferential contribution from HOMO → LUMO and also confirmed that the HOMO-to-LUMO transition for each dye was associated with the largest oscillator strength (f). Data from these TD-DFT calculations, including information about the composition of the electronic transitions, and oscillator strength values, are provided in Table S10. Narrowing of the theoretical HOMO−LUMO gap was observed across the series going from structure 1 to 5 (Figure 10). In the case of dye 6, incorporation of a thiophene unit into the π-system had the effect of lowering both the HOMO and LUMO energy levels. The calculated HOMO−LUMO gap of 6 was comparable in magnitude to that of 5. Overall, the observed trends arising from our theoretical calculations were in good agreement with experimental results.

Figure 10. Energy diagram of the frontier molecular orbitals of 1−6 as estimated by DFT calculations.

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CONCLUSION In summary, a series of new push−pull D−π−A dyes featuring the SF5 acceptor has been synthesized and characterized by UV−vis and fluorescence spectroscopy, cyclic voltammetry, DFT calculations, and single-crystal X-ray diffraction. The six dyes displayed pronounced solvatofluorochromism in solution, indicative of strong ICT effects and push−pull character in these linear π-conjugated dyads. Also notable were the large Stokes shifts (>100 nm) exhibited by the dyes, a property that is of great value in bioimaging. Single-crystal X-ray analysis revealed extensive supramolecular C−H···F interactions that may be potentially useful as a tool for crystal engineering. Solid11016


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The Journal of Organic Chemistry state fluorescence studies showed that molecules 1−6 were also emissive in crystalline and powdered forms. Mechanofluorochromism was visually observable with dye 5, in which the emission of the finely ground powder was blue-shifted relative to pristine crystals. This chromic phenomenon was found to be reversible in subsequent studies employing grinding-fuming cycles. All in all, the pentafluorosulfanyl moiety is an intriguing functional group that deserves further exploration in the context of functional organic molecules and materials.

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room temperature and extracted with dichloromethane. The resulting organic layer was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated, and the residue was purified by silica gel column chromatography using hexane and dichloromethane (9:1 v/v) as eluent to give compound 1 (0.82 g, 52%) as a white solid. Mp: 145.5−146.5 °C. 1H NMR (400 MHz, CDCl3): δ 7.79−7.75 (m, 2H), 7.60 (d, 2H, J = 8 Hz), 7.45−7.42 (m, 2H), 7.30−7.25 (m, 4H), 7.15− 7.12 (m, 6H), 7.08−7.04 (m, 2H). 13C NMR (100 MHz, CDCl3): δ 152.3 (apparent t, J = 17 Hz), 148.4, 147.4, 144.0, 132.2, 129.4, 127.9, 126.5, 126.4 (quintet, J = 5 Hz), 124.9, 123.5, 123.2. 19F NMR (282 MHz, CDCl3): δ 85.13 (quintet, 1F, J = 152 Hz), 63.29 (d, 4F, J = 152 Hz). HRMS (EI-magnetic sector) m/z: [M]+ calcd for C24H18F5NS 447.1080, found 447.1049. UV−vis (DCM), λmax [ε (104 L·mol−1· cm−1)]: 347 [5.3] nm. Synthesis of Compound 2. To a deoxygenated mixture of 4bromophenylsulfur pentafluoride 9 (0.080 g, 0.28 mmol), 4-(N,Ndiphenylamino)styrene 11 (0.084 g, 0.31 mmol), Pd(OAc)2 (4.5 mg, 0.020 mmol), K2CO3 (0.047 g, 0.34 mmol), and tetra-n-butylammonium bromide (0.106 g, 0.330 mmol) was added anhydrous DMF (5 mL). The reaction mixture was stirred at 110 °C for 18 h before being poured into 30 mL of deionized water and extracted with dichloromethane. The resulting organic layer was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated, and the residue was purified by silica gel column chromatography using hexane and dichloromethane (9:1 v/v) as eluent to give compound 2 (0.83 g, 62%) as a light-green solid. Mp: 140.0−141.0 °C. 1 H NMR (400 MHz, CDCl3): δ 7.71−7.68 (m, 2H), 7.51 (d, 2H, J = 8 Hz), 7.39−7.38 (d, 2H, J = 8 Hz), 7.29−7.23 (m, 4H), 7.14−7.10 (m, 5H), 7.07−7.03 (m, 4H), 6.95 (d, 1H, J = 16 Hz). 13C NMR (100 MHz, CDCl3): δ 152.3 (apparent t, J = 17 Hz), 148.2, 147.4, 141.0, 131.5, 130.2, 129.4, 127.8, 126.3 (quintet, J = 4 Hz), 126.0, 124.8, 124.4, 123.4, 123.0. 19F NMR (282 MHz, CDCl3): δ 85.26 (quintet, 1F, J = 147 Hz), 63.18 (d, 4F, J = 150 Hz). HRMS (EI-magnetic sector) m/z: [M]+ calcd for C26H20F5NS 473.1237, found 473.1245. UV−vis (DCM), λmax [ε (104 L·mol−1·cm−1)]: 386 [5.7] nm. Synthesis of Compound 3. To a mixture of deoxygenated toluene (10 mL) and diisopropylamine (5 mL) were added 4bromophenylsulfur pentafluoride 9 (0.080 g, 0.28 mmol), 4-(N,Ndiphenylamino)-ethynylbenzene 12 (0.092 g, 0.34 mmol), Pd(PPh3)4 (17 mg, 0.014 mmol), and CuI (2.6 mg, 0.014 mmol), and the mixture was stirred under nitrogen at 80 °C for 12 h. After workup with CH2Cl2/NH4Cl (aq), the combined organic layers were dried over anhydrous sodium sulfate and filtered. The crude product was purified by silica gel column chromatography using hexane and dichloromethane (9:1 v/v) as eluent to afford compound 3 (0.101 g, 76%) as a pale green solid. Mp: 137.5−138.5 °C. 1H NMR (400 MHz, CDCl3): δ 7.73−7.69 (m, 2H), 7.55 (d, 2H, J = 8 Hz), 7.39−3.36 (m, 2H), 7.31−7.27 (m, 4H), 7.13−7.07 (m, 6H), 7.03−6.99 (m, 2H). 13C NMR (100 MHz, CDCl3): δ 152.7 (apparent t, J = 17 Hz), 148.6, 147.0, 132.8, 131.4, 129.5, 127.5, 126.0 (quintet, J = 5 Hz), 125.2, 123.9, 121.9, 114.7, 93.0,86.7. 19F NMR (282 MHz, CDCl3): δ 84.25 (quintet, 1F, J = 147 Hz), 62.76 (d, 4F, J = 150 Hz). HRMS (EImagnetic sector) m/z: [M]+ calcd for C26H18F5NS 471.1080, found 471.1062. UV−vis (DCM), λmax [ε (104 L·mol−1·cm−1)]: 368 [4.2] nm. Synthesis of Compound 4. To a mixture of deoxygenated toluene (10 mL) and diisopropylamine (5.0 mL) were added 4bromophenylsulfur pentafluoride 9 (0.040 g, 0.14 mmol), N-(4-(2-(4ethynylphenyl)ethynyl)phenyl)-N-phenylbenzenamine 13 (0.063 g, 0.17 mmol), Pd(PPh3)4 (8 mg, 0.007 mmol), and CuI (1 mg, 0.007 mmol), and the mixture was stirred under nitrogen at 80 °C for 20 h. After workup with CH2Cl2/NH4Cl (aq), the combined organic layers were dried over anhydrous sodium sulfate and filtered. The crude product was purified by silica gel column chromatography using hexane and dichloromethane (9:1 v/v) as eluent to give compound 3 (0.058 g, 72%) as a light green solid. Mp: 185.5−186.5 °C. 1H NMR (400 MHz, CDCl3): δ 7.74−7.71 (m, 2H), 7.58 (d, 2H, J = 8 Hz), 7.49 (s, 4H), 7.38−7.35 (m, 2H), 7.30−7.24 (m, 4H), 7.13−7.04 (m, 6H), 7.02−6.99 (m, 2H). 13C NMR (100 MHz, CDCl3): δ 153.10 (apparent t, J = 17 Hz), 148.3, 147.1, 132.6, 131.7, 131.6, 131.5, 129.4,

EXPERIMENTAL SECTION

Materials and Methods. All synthetic procedures were performed in oven-dried glassware under anhydrous nitrogen atmosphere using standard Schlenk techniques. Reagents and solvents were purchased from Sigma-Aldrich, Alfa Aesar, TCI America, and Fisher Scientific and used without further purification. Reaction solvents were dried over activated 3 Å molecular sieves. Crude products were purified by flash column chromatography on silica gel 60−230 mesh. 1H, 13C, and 19 F NMR spectra were recorded on a Bruker AVANCE II 400 MHz and a Bruker AVANCE II 300 MHz NMR spectrometer. Chemical shifts are reported relative to TMS (1H: δ = 0.00 ppm), CDCl3 (1H: δ = 7.26 ppm; 13C: δ = 77.0 ppm), and (CD3)2CO (1H: δ = 2.05 ppm; 13 C: δ = 29.84 ppm). HRMS were recorded on a Kratos ConceptMagnetic Sector Electron Impact mass spectrometer. UV−visible spectra were recorded on a Cary 60 UV−vis and Cary 7000 spectrophotometer. PL spectra were recorded on a Horiba Fluorolog-3 spectrofluorometer. The fluorescence quantum yields (ΦF) of dyes 1−6 were calculated by the steady-state comparative method using quinine sulfate (QS) in 0.5 M sulfuric acid as a standard (Φst = 0.577). Fluorescence lifetimes were measured using an Easylife LS (Photon Technology International). Thin films were obtained by spin-coating using the MB SC-210. Cyclic voltammetry (CV) studies were carried out on a PARSTAT 2273 electrochemical workstation with a conventional three-electrode configuration consisting of a platinum wire working electrode, a platinum mesh counter-electrode, and a silver wire pseudoreference electrode. The experiments were performed at room temperature using 1 × 10−3 M solutions of analyte in HPLC-grade dichloromethane with 0.1 M tetra-n-butylammonium hexafluorophosphate (Bu4NPF6) as the supporting electrolyte. Deoxygenation of the solutions was achieved by sparging with nitrogen for 30 min, and the working electrode was cleaned after each run. The cyclic voltammograms were recorded using a scan rate of 100 mV s−1. Potentials measured with reference to the Ag electrode were calibrated against a ferrocenium/ferrocene (Fc+/Fc, E° = 0.40 V). Density functional theory (DFT) calculations: The initial structures of the SF5-containing molecules were constructed using the GaussView 5.0 visualization program. Geometry optimizations were performed using Gaussian09 at the B3LYP level of theory and the 6-31G(d) basis set. The TDDFT calculation was done from the geometrically optimized structure with the same level of theory and basis set. The single-crystal X-ray diffraction data was collected on a Bruker APEX II diffractometer with graphite-monochromatized Mo−Kα radiation (λ = 0.71073 Å). Data collection and processing were performed using the Bruker APEX II software package. Semiempirical absorption corrections based on equivalent reflections were applied. The structure was solved by direct methods and refined with full-matrix least-squares procedures using SHELX and WinGX. All non-hydrogen atoms were refined anisotropically. The positions of all hydrogen atoms were calculated based on the geometry of related non-hydrogen atoms. No restraints or constraints were applied during the refinement. Powder X-ray diffraction studies were carried out on a Rigaku Ultima IV Diffractometer. Synthesis of Compound 1. 4-(Diphenylamino)phenylboronic acid 10 (0.11 g, 0.38 mmol), 4-bromophenylsulfur pentafluoride 9 (0.10 g, 0.35 mmol), Cs2CO3 (0.25 g, 0.76 mmol), and Pd(PPh3)4 (6 mg, 0.005 mmol) were added to a deoxygenated mixture of toluene (5 mL) and water (1 mL). The mixture was stirred and heated at 110 οC for 16 h under nitrogen atmosphere. The mixture was then cooled to 11017


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140.0 °C. 1H NMR (400 MHz, CDCl3): δ 7.89−7.85 (m, 2H), 7.71 (d, 2H, J = 8 Hz) 7.52−7.48 (m, 1H), 7.40−7.35 (m, 4H), 7.33−7.30 (m, 1H), 7.25−7.18 (m, 7H), 7.14−7.11 (m, 2H), 6.99−6.94 (m, 3H). 13 C NMR (75.4 MHz, CDCl3): δ 169.7, 156.5 (apparent t, J = 19 Hz), 153.5, 151.8, 148.7, 145.1, 137.2, 135.1, 133.5, 133.34, 133.3, 130.0, 129.8, 127.4 (quintet, J = 4.5 Hz), 126.6, 126.4, 126.3, 126.1, 126.0, 119.3, 113.9, 113.8, 112.1, 111.6, 90.1, 75.6. 19F NMR (282 MHz, CDCl3): δ 81.7 (1F, quintet, J = 150 Hz), 62.3 (4F, d, J = 150 Hz). HRMS (EI-magnetic sector) m/z: [M]+ calcd for C38H22F5N5S, 675.1516, found 675.1544. UV−vis (DCM), λmax [ε (104 L·mol−1· cm−1)]: 667 [1.9] nm. Synthesis of Compound 13. To a mixture of deoxygenated methanol (10 mL) and tetrahydrofuran (5 mL) were added N-(4-(2(4-(2-(trimethylsilyl)ethynyl)phenyl)ethynyl)phenyl)-N-phenylbenzenamine (0.20 g, 0.45 mmol) and K2CO3 (0.310 g, 2.24 mmol). The reaction mixture was then stirred under nitrogen atmosphere for 6 h. Upon completion, the reaction mixture was diluted with CH2Cl2 and washed with saturated NH4Cl (aq) solution. The organic phase was dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography using hexanes and dichloromethane (9:1 v/v) as eluent to give compound 13 (0.143 g, 86%) as a pale yellow solid. Mp: 163.5−164.5 °C. 1H NMR (400 MHz, CDCl3) δ 7.44 (s, 4H), 7.37− 7.34 (m, 2H), 7.29−7.24 (m, 4H), 7.12−7.04 (m, 6H), 7.01−6.98 (m, 2H), 3.15 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 148.2, 147.1, 132.6, 132.0, 131.3, 129.4, 125.1, 124.2, 123.6, 122.1, 121.4, 115.6, 91.8, 88.2, 83.4, 78.7. HRMS (EI-magnetic sector) m/z: [M]+ calcd for C28H19N 369.1517, found 369.1515. Synthesis of Compound 15. To a mixture of deoxygenated toluene (10 mL) and diisopropylamine (10 mL) were added ((5bromothiophene-2-yl)ethynyl)trimethylsilane (0.228 g, 1.11 mmol), 4ethynyltriphenylamine (0.237 g, 1.11 mmol), Pd(PPh3)4 (51 mg, 0.060 mmol), and CuI (4.2 mg, 0.030 mmol), and the mixture was stirred under nitrogen atmosphere at 80 °C overnight. The cooled mixture was diluted with CH2Cl2 and filtered through a pad of Celite, after which the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography using hexanes and dichloromethane (8.5:1.5 v/v) as the eluent to give N,Ndiphenyl-4-((5-((trimethylsilyl)ethynyl)-2-thiophene-yl)ethynyl)aniline as a yellow oil. Yield: 0.250 g, 50%. 1H NMR (400 MHz, CDCl3): δ 7.37−7.34 (m, 2H), 7.31−7.27 (m, 4H), 7.14−7.05 (m, 8H), 7.00 (d, 2H, J = 8 Hz), 0.27 (s, 9H). 13C NMR (100 MHz, CDCl3): δ 148.6, 147.4, 132.9, 132.8, 131.4, 129.8, 125.5, 125.48, 124.4, 124.1, 122.3, 115.4, 100.2, 97.5, 94.7, 81.8, 0.16. A mixture of deoxygenated methanol (10 mL) and tetrahydrofuran (5 mL) was charged with N,N-diphenyl-4-((5-((trimethylsilyl)ethynyl)-2-thiophene-yl)ethynyl)aniline (0.20 g, 0.45 mmol) and K2CO3 (0.310 g, 2.24 mmol), and the reaction mixture was stirred under nitrogen atmosphere for 4 h. Upon completion, the reaction mixture diluted with dichloromethane and washed with saturated aqueous NH4Cl solution. The organic phase was dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography using hexanes and dichloromethane (9:1 v/v) as the eluent to afford compound 15 as an orange solid. Yield: 0.163 g, 97%. Mp: 147.5−148.5 °C. 1H NMR (400 MHz, (CD3)2CO): δ 7.42−7.34 (m, 6H), 7.27 (d, 1H, J = 4 Hz), 7.21 (d, 1H, J = 4 Hz), 7.16−7.12 (m, 6H), 6.98−6.95 (m, 2H), 4.09 (s, 1H). 13C NMR (100 MHz, (CD3)2CO) δ 149.6, 147.8, 134.1, 133.3, 132.3, 130.4, 126.2, 125.8, 125.0, 123.6, 122.1, 115.2, 95.1, 84.4, 81.4, 76.7. HRMS (EI-magnetic sector) m/z: [M]+ calcd for C26H17NS 375.1082, found 375.1080.

126.9, 126.1 (quintet, J = 5 Hz), 125.1, 124.4, 123.7, 122.1, 121.6, 115.5, 92.2, 92.21, 88.9, 88.2. 19F NMR (282 MHz, CDCl3): δ 82.78 (quintet, 1F, J = 150 Hz), 61.5 (d, 4F, J = 150 Hz). HRMS (EImagnetic sector) m/z: [M]+ calcd for C34H22F5NS 571.1393, found 571.1399. UV−vis (DCM), λmax [ε (104 L·mol−1·cm−1)]: 380 [9.6] nm. Synthesis of Compound 5. To a mixture of 4-bromophenylsulfur pentafluoride 9 (0.065 g, 0.23 mmol), 14 (0.086 g, 0.23 mmol), Pd(OAc)2 (1.5 mg, 0.0069 mmol), K2CO3 (0.318 g, 2.30 mmol), and tetrabutylammonium bromide (0.148 g, 0.460 mmol) was added anhydrous DMF (5 mL). The reaction mixture was stirred at 110 °C for 18 h before being poured into 30 mL of water and extracted with dichloromethane. The resulting organic layer was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated, and the residue was purified by silica gel column chromatography using hexane and dichloromethane (9:1 v/v) as eluent to afford compound 5 (0.090 g, 68%) as a light-yellow solid. Mp: 232.0−233.0 °C. 1H NMR (400 MHz, (CD3)2CO): δ 7.88−7.81 (m, 4H), 7.67− 7.61 (m, 4H), 7.54 (d, 2H, J = 8 Hz), 7.46 (d, 1H, J = 16 Hz), 7.38− 7.27 (m, 6H), 7.17 (d, 1H, J = 16 Hz), 7.10−7.06 (m, 6H), 7.02 (d, 2H, J = 8 Hz). 13C NMR (75.4 MHz, CDCl3): δ 152.5 (apparent t, J = 17 Hz), 147.6, 147.5, 140.7, 137.9, 135.3, 131.6, 131.2, 129.3, 128.7, 127.4, 127.2, 126.7, 126.4, 126.3, 126.25, 125.9, 124.6, 123.4, 123.1. 19 F NMR (282 MHz, CDCl3): δ 85.05 (quintet, 1F, J = 147 Hz), 63.1 (d, 4F, J = 150 Hz). HRMS (EI-magnetic sector) m/z: [M]+ calcd for C34H26F5NS 575.1706, found, 575.1689. UV−vis (DCM), λmax [ε (104 L·mol−1·cm−1)]: 403 [9.9] nm. Synthesis of Compound 6. To a mixture of deoxygenated toluene (10 mL) and diisopropylamine was added 4-((5-ethynylthiophene-2-yl)ethynyl)-N,N-diphenylaniline 15 (0.102 g, 0.270 mmol), 4-bromophenylsulfur pentafluoride 9 (0.080 g, 0.28 mmol), Pd(PPh3)4 (16 mg, 0.014 mmol), and CuI (1.3 mg, 0.007 mmol). The reaction mixture was stirred under nitrogen atmosphere at 80 °C for 16 h. The cooled mixture was diluted with CH2Cl2 and filtered through a pad of Celite, after which the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography using hexane and dichloromethane (9:1 v/v) as eluent to afford compound 6 (0.127 g, 80%) as an orange solid. Mp: 178.5−179.5 °C. 1 H NMR (400 MHz, (CD3)2CO): δ 7.95 (d, 2H, J = 8 Hz)), 7.78 (d, 2H, J = 8 Hz), 7.44−7.35 (m, 7H), 7.29 (d, 1H, J = 4 Hz), 7.17−7.13 (m, 6H), 6.97 (d, 2H, J = 8 Hz). 13C NMR (75.4 MHz, CDCl3): δ 153.1 (apparent t, J = 17 Hz), 148.4, 147.0, 132.8, 132.5, 131.4, 131.34, 129.4, 126.4, 126.38, 126.09 (quintet, J = 4.5 Hz), 125.2, 123.8, 122.78, 121.8, 114.7, 95.2, 91.8, 85.5, 81.3. 19F NMR (282 MHz, CDCl3): δ 83.75 (quintet, 1F, J = 147 Hz), 62.09 (d, 4F, J = 147 Hz). HRMS (EImagnetic sector) m/z: [M]+ calcd for C32H20F5NS2 577.0957, found 577.0958. UV−vis (DCM), λmax [ε (104 L·mol−1·cm−1)]: 395 [2.1] nm. Synthesis of Compound 7. TCNE (16.0 mg, 0.127 mmol) was added to a mixture of compound 3 (60.0 mg, 0.127 mmol) in dichloromethane (20 mL). The mixture was refluxed at 40 °C for 24 h. The solvent was removed in vacuo, and the crude product was subjected to silica gel column chromatography using hexane and dichloromethane (3:7 v/v) as eluent to afford compound 7 (0.061 g, 80%) as a dark brown solid. Mp: 129.5−130.5 °C. 1H NMR (400 MHz, CDCl3): δ 7.94−7.90 (m, 2H), 7.78 (d, 2H, J = 8.6 Hz), 7.67− 7.63 (m, 2H), 7.44−7.40 (m, 4H), 7.31−7.23 (m, 6H), 6.97−6.93 (m, 2H). 13C NMR (75.4 MHz, CDCl3): δ 166.5, 162.1, 157.1 (apparent t, J = 14 Hz), 154.2, 144.2, 134.4, 131.8, 130.2, 129.7, 127.6 (quintet, J = 4 Hz), 127.1, 127.0, 120.2, 118.1, 113.2, 112.8, 111.0, 110.5, 90.5, 77.6. 19 F NMR (282 MHz, CDCl3): δ 80.12 (quintet, 1F, J = 150 Hz), 61.02 (d, 4F, J = 150 Hz). HRMS (EI-magnetic sector) m/z: [M]+ calcd for C32H18F5N5S 599.1203, found 599.1181. UV−vis (DCM), λmax [ε (104 L·mol−1·cm−1)]: 485 [2.0] nm. Synthesis of Compound 8. TCNQ (26.0 mg, 0.127 mmol) was added to a mixture of compound 3 (60.0 mg, 0.127 mmol) in chloroform (30 mL). The mixture was refluxed at 60 °C for 64 h. The solvent was removed in vacuo, and the crude product was subjected to silica gel column chromatography using dichloromethane as eluent to give compound 8 (0.026 g, 30%) as a dark green solid. Mp: 139.0−

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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.joc.7b01972. Characterization data for all new compounds; 1H, 13C, and 19F NMR spectra of new compounds; thin film 11018


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absorption and emission spectra; DFT and TD-DFT calculation data, and electrochemical (i.e., cyclic voltammetry) data for compounds 1−8; PXRD data for compound 5 (PDF) X-ray data for compounds 1 (CCDC: 1565905), 2 (CCDC: 1565906), 3 (CCDC: 1565907), 4 (CCDC: 1565908), 5 (CCDC: 1565909), and 6 (CCDC: 1565910) (CIF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Julian M. W. Chan: 0000-0002-2734-6496 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the Natural Sciences and Engineering Research Council (NSERC Discovery Grant; RGPIN-2016-04614), the Canada Foundation for Innovation (CFI) John R. Evans Leaders Fund (CFI-JELF project no. 34474), the Ministry of Research and Innovation (MRI), and the University of Ottawa.

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