StructureâProperty Studies of Bichromophoric, PAH-Functionalized

Article pubs.acs.org/Organometallics

Structure−Property Studies of Bichromophoric, PAH-Functionalized Dithieno[3,2-b:2′,3′-d]phospholes Chris Jansen Chua, Yi Ren, and Thomas Baumgartner* Department of Chemistry & Centre for Advanced Solar Materials, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada S Supporting Information *

ABSTRACT: A series of dithienophospholes featuring polyaromatic hydrocarbon (PAH) substituents, with increasing number of fused rings ranging from 2 to 4 at the phosphorus center, have been synthesized and characterized. The installation of a large π-system in the vicinity of the dithienophosphole scaffold was found to induce unusual photophysics for this system that are based on the creation of two neighboring chromophores within the same molecular scaffold. Extensive photophysical studies revealed that significant energy transfer (ET) occurs from the PAH unit, which acts as a donor, to the dithienophosphole acceptor, showing ET efficiencies of almost 90%. TD-DFT calculations confirm the possibility for the two subunits to communicate with each other. Furthermore, due to the presence of the out-of-plane dithienophosphole unit, the PAH species do not show any significant tendency to form aggregates, such as excimers/exciplexes, even in colloidal suspensions.

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INTRODUCTION The development of functional π-conjugated chromophores is an active field of research, as many of these organic materials have found practical application in organic light-emitting diodes (OLEDs), organic field-effect transistors, organic photovoltaics, and a variety of sensing applications.1 One of the advantages of using organic components for this purpose is the bottom-up approach, allowing for assembly of functional materials by design from the atomic level. Research in recent years has shown that the incorporation of inorganic main group components into the scaffold of organic materials has tremendous potential for further effectively tuning the properties of π-conjugated chromophores, due to the intrinsic nature of the heteroelements. Boron,2 silicon,3 and phosphorus3 have been among the strongest contenders for efficiently manipulating the photophysical and electronic properties of organic materials. Along these lines, we have established the dithieno[3,2-b:2′,3′-d]phosphole scaffold I (Chart 1), which exhibits very intriguing photophysical properties with respect to wavelength, intensity, and tunability.5 Others and we could establish that phosphorus-based materials generally add considerable value to organic materials, as simple modification of the phosphorus center (E, Chart 1) has significant impact on the materials’ electronic properties; whole families of derivatives are accessible from a central trivalent phosphorus species.4,5 Furthermore, the presence of the phosphorus center can increase the electron-acceptor properties of these materials, providing an excellent conduit for the generation of semiconductor materials with highly desirable n-channel preference.6 We have now extended our studies by focusing on new dithienophospholes with exocyclic polyaromatic hydrocarbon substituents (PAHs) in place of the phenyl group (II, Chart 1) © 2012 American Chemical Society

Chart 1. Classic Dithieno[3,2-b:2′,3′-d]phospholes I and the New PAH-Based Systems II

to further explore the structure−property relationship of this system. Due to the pyramidal nature of the phosphorus center, the exocylic substituents are not in π-conjugation with the main scaffold, potentially resulting in some interesting photophysics for the system. Both the PAH moiety and the dithienophosphole scaffold should behave as independent fluorophores, and their close proximity would provide for communication through, for example, energy-transfer processes between the designated donor (D) and acceptor (A) parts in this molecular architecture. Due to its comparatively lower HOMO−LUMO gap, the dithienophosphole unit was considered the acceptor, while the PAH components in turn would act as the donor in these systems. Related PAH π-donor systems have already successfully been employed in a D−A energy transfer (ET) motif in the literature.7 It is important to note that because of the rigid planar structure of the PAH units, excimer or exciplex Received: January 18, 2012 Published: March 5, 2012 2425

dx.doi.org/10.1021/om3000407 | Organometallics 2012, 31, 2425−2436

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formation is generally possible with these systems, which could lead to significantly altered photophysics or even quenched luminescence.8 However, the attachment of PAH units to the dithienophosphole building block introduces an out-of-plane component, thereby providing a means for restricting the PAHs' face-to-face π-interaction and to potentially preserve the photophysics of the molecular framework. In this contribution we now report the synthesis and characterization of a new series of dithienophospholes with exocyclic PAH substituents including naphthyl, phenanthryl, and pyrenyl species to investigate the effects of increasing chromophore size at the phosphorus center. Studies toward the communication between the two subchromophores, as well as the aggregation behavior, have also been addressed, and the experimental results were verified via theoretical calculations.

Scheme 1. Synthesis of the PAH-Functionalized Dithienophospholes

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RESULTS AND DISCUSSION Synthesis and Characterization. In order to circumvent potential insolubility issues arising from the extended planar PAH scaffolds, and to further investigate the impact of varying degree of steric bulk at the dithienophosphole scaffold on the aggregation behavior of the new species, we have targeted three series of pyrenyl compounds with either −H, −SiMe3, or −SiMe2tBu substituents at the 2,6-positions. The general synthesis of the new dithienophospholes involves the lithiation of a suitable dibromobithiophene species (1a,b,c) followed by the addition of (PAH)PCl2 (PAH = 1naphthyl, 9-phenanthryl, 1-pyrenyl) at low temperatures according to our established procedures (Scheme 1).5a−e While the trivalent-phosphorus compounds 2b, 4a, and 4c could be obtained in pure form after workup in moderate to good yields, pure 3b and 4b, however, could not be isolated. Consequently, the crude compounds 3b and 4b were directly oxidized without further characterization to obtain the corresponding pentavalent forms (vide inf ra). Naphthyl species 2b was obtained as light yellow solid in 64% yield and shows a 31P{1H} NMR chemical shift at δ = −30.9 ppm, slightly upfield-shifted with respect to the P-phenyl congener Ib-lp (Chart 1; δ = −25.0 ppm),5b which can be attributed to the electronically and sterically extended naphthyl unit affecting the overall geometry and concomitant shielding of the phosphorus center. Compound 4a was isolated in pure form after recrystallization, affording clear, light yellow crystals with a moderate yield of 57%. This species shows a 31P{1H} NMR shift at δ = −28.5 ppm, which is also upfield-shifted relative to its P-phenyl congener Ia-lp (Chart 1; δ = −21.5 ppm).5a The 31P{1H} NMR spectrum of the pale yellow 4c that could be obtained in 68% yield exhibits a chemical shift at δ = −33.5 ppm, slightly more upfield-shifted than its P-phenyl relative Ic-lp (Chart 1; δ = −27.4 ppm), which can again be attributed to the effects of the fused PAH substituent. It is also upfield-shifted relative to 4a, due to the presence of the electron-accepting silyl units.5a,b 1H and 13C NMR spectroscopy, as well as high-resolution mass spectrometry, further confirm the identity of the three new trivalent dithienophospholes. To further gauge the effects of a chemically modified phosphorus center on the overall photophysics as well as the aggregation behavior, these three compounds and the crude 3b and 4b were oxidized at the phosphorus center via the addition of excess H2O2 and were subsequently purified by column chromatography to produce oxidized dithienophospholes in moderate to good yields (5b = 73%, 6b = 63%, 7a = 84%, 7b =

50%, 7c = 55%); the methylated 8 was obtained from 4c in 74% yield after addition of an excess of MeOTf (Scheme 1). The 31P{1H} NMR chemical shifts for 5b at δ = 21.3 ppm, 6b at δ = 21.0 ppm, and 7b at δ = 21.9 ppm are very similar but are, however, more downfield-shifted with respect to the reference compound Ib-O (Chart 1; δ = 17.2 ppm).5b This is contrary to the observations for the corresponding trivalent PAH-functionalized species supporting a more pronounced effect of the P-functionalization on the electronic properties of these systems. The 31P{1H} NMR spectrum of 7a displays a resonance at δ = 23.3 ppm, which is also more downfieldshifted than that of both 7b (δ = 21.9 ppm) and 7c (δ = 22.3 ppm), as well as the reference compound Ia-O (Chart 1; δ = 18.8 ppm).5a As for 7c, with the bulkier tert-butyldimethylsilyl (TBDMS) groups in the 2,6-position of the dithienophosphole scaffold, its 31P{1H} NMR shift at δ = 22.3 ppm is slightly shifted downfield compared to the Me3Si-functionalized species; it also exhibits a significant downfield shift from the P-phenyl compound Ic-O (Chart 1; δ = 14.9 ppm). The 31 1 P{ H} NMR spectrum of the phospholium species 8 shows a shift at δ = 7.9 ppm, which is significantly downfield-shifted with respect to the trivalent congener 4c, in line with earlier observations for the P-phenyl relatives.5c The formation of 2426


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these P-modified species was also confirmed with consistent 1H and 13C NMR spectroscopy, as well as HRMS data and elemental analysis. Moreover, single crystals suitable for X-ray crystallography were obtained for 7b from a concentrated acetone solution at room temperature upon slow evaporation of the solvent (Figure 1). The bond lengths and angles within the scaffold are

Figure 2. Molecular structure of 7a (top) and intermolecular interactions (bottom) in the solid state (50% probability level, hydrogen atoms are omitted for clarity). Selected bond lengths [Å] and angles [deg]: P1−C3: 1.814(2), P1−C6: 1.804(2), P1−C11: 1.808(2), P1−O1: 1.488(17), C1−C2: 1.365(3), C2−C3: 1.414(3), C3−C4: 1.386(3), C4−C5: 1.454(3), C5−C6: 1.380(3), C6−C7: 1.425(3), C7−C8: 1.368(3); C3−P1−C11: 107.43(10), C6−P1− C11: 105.26(11), C3−P1−O1: 117.73(10), C6−P1−O1: 117.99(10), C11−P1−O1: 113.81(10).

C3−C4 = 1.374(4) Å).5b,c In addition, face-to-face π-stacking interactions are again observed, but this time not only between the pyrenyl units at 3.6 Å but also between the nonfunctionalized dithienophosphole units at 3.5 Å, supporting the steric effect of the silyl substituents in 7b. We were also able to grow single crystals of 7c, which unfortunately did not provide satisfactory X-ray data to warrant a detailed discussion. However the organization in the solidstate clearly supports the fact that the increased steric bulk of the tBuMe2Si substituents further reduces the tendency for intermolecular π-stacking; almost none of the pyrenyl units show such interactions (see Supporting Information). Photophysical Studies. The photophysical properties of the PAH-functionalized dithienophospholes were investigated in CH2Cl2 solution (∼10−5 M), and the results are listed in Table 1. The trivalent phosphole derivatives show distinctly different absorption spectra, due to the increasing impact of the PAH substituent. While 2b exhibits the dithienophospholetypical, essentially featureless absorption profile, albeit with a transition that can be assigned to the naphthyl unit (λabs = 312 nm; vide inf ra), 4a, with the pyrenyl unit, shows the typical vibronic sidebands of pyrene (Figure 3).9 Compared to pyrene, the addition of a dithienophosphole moiety also induces a significant red-shift in the absorption spectra, indicating the electronic interaction between pyrenyl and the dithienophosphole core; similar results have been observed before.9c,d The naphthyl derivative 2b exhibits blue emission at λem = 421 nm, which is typical for dithienophospholes (Ia-lp, Ib-lp, Ic-lp: λem = 415−422 nm),5a,b while the dithienophosphole-typical featureless fluorescence emission for 4a and 4c exhibits highly uncharacteristic bathochromic shifts of Δλem = 29 and 39 nm, respectively.

Figure 1. Molecular structure of 7b (top) and intermolecular interaction (bottom) in the solid state (50% probability level, hydrogen atoms are omitted for clarity). Selected bond lengths [Å] and angles [deg]: P1−C3: 1.814(3), P1−C6: 1.818(3), P1−C11: 1.801(3), P1−O1: 1.483(2), C1−C2: 1.378(4), C2−C3: 1.424(4), C3−C4: 1.374(4), C4−C5: 1.454(4), C5−C6: 1.382(4), C6−C7: 1.427(4), C7−C8: 1.373(4), Si1−C1: 1.875(3), Si2−C8: 1.876(3); C3−P1−C11: 116.28(12), C6−P1−C11: 106.93(12), C3−P1−O1: 118.29(13), C6−P1−O1: 116.14(12), C11−P1−O1: 114.74(13).

in accordance with previously reported solid-state structures of oxidized dithienophospholes with a P-phenyl substituent.5b,d The high degree of conjugation within the main scaffold can be observed in the short single bonds and in the elongated double bonds. The molecular packing (Figure 1, bottom) illustrates the face-to-face π-stacking interaction at 3.5 Å between the pyrenyl units, supporting its propensity for this kind of intermolecular interaction. As expected, the bulky Me3Si groups prevent such intermolecular interactions for the main dithienophosphole scaffold. The successful formation of 7a was also additionally confirmed by single-crystal X-ray crystallography; suitable crystals were obtained from a concentrated CH2Cl2 solution upon slow evaporation of the solvent (Figure 2). Overall, both the bond lengths and angles are in good agreement with previously reported oxidized dithienophospholes.5b,d,e The absence of electron-accepting silyl groups seemingly contributes to the bond shortening/elongation of the system (e.g., 7a: C1−C2 = 1.365(3), C7−C8 = 1.368(3), and C3−C4 = 1.386(3) Å; 7b: C1−C2 = 1.378(4), C7−C8 = 1.373(4), and 2427


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Table 1. Photophysical Data for the PAH-Based Phospholes in CH2Cl2 (∼10−5 M) and the Solid State solution λabs [nm]a

compound Ia-lp5a,i Ib-lp5b Ic-lp5a,b 2b 4a 4c Ib-O5b Ic-O5b 5b 6b 7a 7b 7c 8

εmax [L mol−1 cm−1]b

312, 348 280, 342, 357 279, 344, 360

24 000 18 200 32 000 22 000 52 000 38 000

362 258, 302, 272, 272, 272, 278,

21 000 10 000 13 000 33 000 21 000 29 000 42 000

297, 379 283, 283, 282, 285,

378 355, 309, 315, 364,

365, 381 355,364, 381 355,366, 381 370, 386

λex [nm]c 338 344 364 309, 276, 273, 374 365 251, 254, 273, 275, 274, 283,

350 359 360

296, 381 303, 381 365 364 364 383

solid state λem [nm]d

Stokes shift [cm−1]

415 422 422 421 450 460 460 453 455 455 453 460 460 466

5500 5400 3800 5000 5800 6000 5000 5300 4500 4400 5500 5900 5900 4400

λex [nm]c

λem [nm]d

288, 371 285, 400 305, 388

444 470 467

290, 284, 412 314, 315, 313,

458 475 470 477 474 468

368 416 423 420 417

ϕPLe 0.78 0.60 0.79 0.05 0.16 0.01 0.56 0.57 0.27 0.31 0.20 0.30 0.33 0.17

UV/vis absorption maxima in CH2Cl2. bExtinction coefficient from λmax (bold values). cExcitation maxima (bold values represent π−π* transitions). dEmission maxima, excitation at respective π−π* transitions. ePhotoluminescence quantum yields in CH2Cl2, relative to quinine sulfate; ±10%. a

from 4400 to 6000 cm−1. Both are quite similar to previously reported dithienophosphole compounds;5 however, the large εmax values for the pyrenyl species are again remarkable, as they clearly support the presence of a second chromophore within the scaffold that significantly contributes to the overall photophysics; this is further supported by the red-shifted emission of the pyrenyl species (Figure 3, bottom).5a−c Consequently, the emission of the naphthyl-based system 2b appears to be dominated by the dithienophosphole moiety, while the combination of both the pyrenyl and the dithienophosphole chromophores dominates the photophysics of the pyrenyl-based species 4a,c. As for the silyl-functionalized pyrenyl system 4c, the emission has a 10 nm red-shift compared to the H-functionalized pyrenyl system 4a, similar to the effects observed in the reference compounds I.5a,b In the pentavalent dithienophosphole varieties on the other hand, less impact of the substitution pattern on the photophysical properties of the system is observed (Table 1). The emission only ranges from λem = 453 to 460 nm, regardless of the nature of the PAH. Furthermore, both 5b and 6b have similar absorption and emission spectra to those of the Pphenyl dithienophosphole oxides of type I. These observations indicate that the dithienophosphole core is indeed the major contributor to the photophysical properties of the systems. Compound 7a shows an emission at λem = 453 nm that is slightly blue-shifted relative to both silyl-functionalized pyrene systems (7b: λem = 459 nm; 7c: λem = 460 nm), in line with the electronic effects for the 2,6-silyl substituents.5a,b However, the absorption spectra of the latter three species also exhibit distinct features: all show similar peaks arising from both the pyrenyl and the dithienophosphole unit (see Supporting Information). Finally, the phosphonium salt 8 shows the strongest emission red-shift of all species at λem = 466 nm, which is also in line with earlier studies.5c This is due to the presence of the cationic methylated phosphorus center, making it a stronger acceptor unit, which should concurrently induce more pronounced D−A characteristics within the system. Solid-state emissions are in the range λem = 444−477 nm, with 2b having the largest solution-to-solid-state differential of Δλem = 23 nm and 8 having the least (Δλem = 2 nm), respectively (Table 1). These findings indicate the absence of

The extinction coefficients (εmax) for the compounds are in the range 10 000−52 000 L mol−1cm−1, and Stokes shifts vary

Figure 3. (Top) Normalized absorption of 2b, 4a vs pyrene. (Bottom) Normalized emission of 2b, 4a, and 4c. 2428


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significant intermolecular π-interactions in the solid state, likely due to the bulky nature of the molecules, which in turn is preferable in the study of intramolecular energy transfer between the two subchromophores in diluted solutions. Notably, the photoluminescence quantum yield efficiencies for the new species are surprisingly low. Both silylfunctionalized 2b and 4c display values of only ϕPL = 0.05 and 0.01, while their model compounds, Ib-lp and Ic-lp, have values of ϕPL = 0.60 and 0.79, respectively.5a,b The low values for 2b and 4c are an indication of the presence of nonradiative processes that increase the efficiency of energy-consuming internal conversion, ultimately resulting in a lowered emission intensity.10 The pentavalent compounds show higher values, in the range ϕPL = 0.20−0.33, compared to the trivalent derivatives, but are still lower than their respective literature analogues (Ia-O: 0.57, Ib-O: 0.56, Ic-O: not reported)5a,b and are an indication that the presence of two chromophores within the same molecular scaffold is indeed the main underlying cause for the unusual features. Energy-Transfer Studies. To solidify that the observed photophysical properties are due to the close proximity of the two chromophores, the potential energy transfer between the units was investigated. In particular, the (partial) spectral overlap between the donor’s emission (naphthalene: λem = 320−350 nm, phenanthrene: λem = 350−390 nm, and pyrene: λem = 370−390 nm)9 and the acceptor’s absorption (Ia-lp: λex = 338 nm,5b Ib-lp: λex = 344 nm,5b Ic-lp: λex = 364 nm,5b Ia-Me+: λex = 376 nm,5c Ia-O: λabs = 362 nm,5b Ib-O: λex = 374 nm,5b Ic-O: n/a) could allow for ET to occur (Chart 2).

why 2b has a slightly higher efficiency compared to 5b, which is primarily due to a better spectral overlap of the naphthalene emission and the absorption of Ib-lp vs Ib-O. The phenanthrylbased phosphole oxide 6b also has a good spectral overlap, but surprisingly has a lower efficiency, probably due to a lower orientation factor;8e,f the phenanthryl unit is connected in the 9-position, while both the naphthyl and the pyrenyl units are connected to the 1-position. Because of this, both the emission dipole of phenanthrene and absorption dipole of the dithienophosphole scaffold could contribute to the lowered ETeff, assuming that all other parameters remain constant. As for the pyrenyl-based systems, 4c exhibits a better efficiency at ϕ = 78.5% than 4a at ϕ = 72.1%. The pentavalent forms, on the other hand, all have similar ETeff (ϕ = 81.7−83.5%), including the methylated species 8 at ϕ = 80.7%. As a result, these studies strongly support the electronic communication between the two subchromophores and consequently the presence of nonradiative relaxation pathways that reduce the overall quantum yield efficiency of the system. Excimer Formation Studies. To study whether πaggregates/excimers can be formed (or suppressed) with the PAH-containing dithienophospholes, concentration-dependent photophysics were studied in CH2Cl2 between ∼10−6 and ∼10−3 M. However, none of the compounds showed any notable shifts in their photophysics at varying concentrations (see Supporting Information). Other than the changes in their intensity that correlate with the concentration of the species, the absorption spectra essentially remained identical at all concentrations; only 6b shows a small red-shift from λabs = 379 nm at ∼10−6 M to λabs = 384 nm at ∼10−5 M. Some minor red shifts could also be observed for the emission spectra, however, only for compounds 2b from λem = 424 nm at ∼10−5 M to λem = 455 nm at ∼10−5 M and 4a from λem = 451 nm at ∼10−6 M to λem = 455 nm at ∼10−3 M. The other compounds reveal similar, constant emission profiles over the large concentration ranges applied. The results strongly indicate that none of the PAH-functionalized dithienophospholes have a high propensity to form aggregates via their pendant groups in solution. This observation can likely be attributed to the steric bulk and the electronic effect of the dithienophosphole scaffold on the three PAH scaffolds. Since the pyrenyl group should, in theory, have the highest tendency to form π-aggregates, as indicated by the results of the X-ray crystallography on 7a and 7b, additional representative studies were performed, to explore whether excimer formation can be forced to occur in a colloidal suspension. The studies were conducted in a mixture of MeOH (“good solvent”: 7a and 7b are soluble) and H2O (“bad solvent”: 7a and 7b are only sparingly soluble) at varying ratios, and the photophysical

Chart 2. Potential Energy Transfer (ET) within the Scaffold

The area comparison method, which relates the integrals of the excitiation and absorption spectra of a given compound upon excitation of the donor component, was chosen to quantify the ETeff (ϕ) of the experimentally prepared compounds using CH2Cl2 as solvent.7b,11 This method has also provided useful data for dendrimeric dithienophospholes before.12 The naphthyl-based species demonstrate good efficiencies of ETeff, ϕ = 86.8% and 84.3% for the trivalent and the pentavalent system, respectively. It is understandable

Table 2. Colloidal Suspension Data of the Pyrene-Containing Phospholes 7a

a

MeOH:H2O

λexa

100:0 70:30 60:40 50:50 40:60 30:70 20:80

275, 275, 275, 276, 278, 278,

[nm] 359 359 359 360 361 360

7b λemb

[nm]

460 465 465 465 468 468

7c

8

λex [nm]

b

λem [nm]

λex [nm]

271, 361

465

272, 360

462

272, 275, 275, 276,

469 478 480 480

274, 273, 274, 275,

463 463 463 463

a

361 366 371 366

a

360 358 358 358

λemb

[nm]

λex [nm]

λemb [nm]

274, 376 276, 391

460 462

277, 380

463

358, 380 333, 382

475 484

a

Excitation maxima (bold values represent π−π* transitions). bEmission maxima, excitation at respective π−π* transitions. 2429


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Figure 4. Frontier molecular orbital surfaces and energies for Ib-lp, 2b, and 4b.15

= −1.38 eV), due to the contribution from the pyrenyl moiety (Figure 4). At first glance, the frontier orbitals for both Ib-lp and 2b appear similar, while the electronic distribution in 4b differs significantly, which could explain the differences/ similarities in their respective energy gaps. The HOMO−1, HOMO, and LUMO orbitals of Ib-lp are very similar, wherein they show main contributions from the dithienophosphole scaffold. The HOMO, however, has no contribution from the phosphorus center. The LUMO+1 has representations primarily from the phenyl unit. Judging by the oscillator strength, two transitions (S1 and S2) have to be considered: the HOMO/LUMO transition with a value of f1 = 0.441 and the HOMO−1/LUMO transition with a value of f 2 = 0.126, where both transitions demonstrate the electron density migrating mainly to only the dithienophosphole moiety (Table 3). The calculations show that there is only a minimal interaction between the phenyl pendant group and the dithienophosphole unit. The HOMO−1 of 2b has involvement from both the dithienophosphole and naphthyl moiety; the HOMO and

properties were examined (Table 2). With increasing H2O ratio, the solutions became more turbid, in line with the enhanced hydrophobic effect that was expected to induce πaggregation of 7a and 7b via the “nonpolar” pyrenyl and/or dithienophosphole units. However, increasing the water content of the solution led only to a small bathochromic shift for most of the compounds. In turn, the slight shift in fluorescence could be caused by increasing solvent polarity due to higher H2O content instead of excimer/exciplex formation.5f,8f,14 For the TBDMS-substituted pyrenyl-phosphole oxide 7c, the bathochromic shift was expectedly not observed, while 7a showed a noticeable red-shift of the emssion (Δλem = 8 nm). It is interesting to note, however, that the shift is less prominent for 7a than for the bulkier 7b (Δλem = 15 nm). The cationic 8 displays the strongest effect, having an emission shift of λem = 460 nm at 100:0 ratio to λem = 484 nm at 20:80 ratio (MeOH:H2O), even in the presence of the TBDMS units, which further supports that the polarity of the molecule in its excited state could in fact have a stronger impact on the photophysics than aggregation. All compounds show only minimal change in their respective emission even as more water was added. As a result, the shift in the emission can mainly be attributed to the polarity of the solution as opposed to intermolecular π-stacking interactions.5f,8f,14 Theoretical Calculations. In order to better understand the photophysical characteristics of the synthesized compounds, density functional theory (DFT) calculations have been performed at the B3LYP/6-31G(d) level of theory.15 Molecular orbital energies and distributions were determined, and time-dependent (TD)-DFT was performed to elucidate dynamic excitation processes based on their oscillator strengths (f). To exclusively focus on the electronic effects of the exocyclic PAH substituents on the systems’ overall electronic properties, SiMe3 units were used for all the systems as a representative example. For the trivalent system, 4b shows a narrower energy gap of ΔEH‑L = 3.58 eV (EHOMO = −5.26 to ELUMO = −1.68 eV) compared to both 2b at ΔEH‑L = 3.93 eV (EHOMO = −5.34 to ELUMO = −1.41 eV) and the reference compound Ib-lp at ΔEH‑L = 3.94 eV (EHOMO = −5.32 to ELUMO

Table 3. Calculated Electronic Transitions and Relevant Oscillator Strengths (f) for Ib-lp, 2b, and 4ba transition

Ib-lp

2b

λ [nm] f S1

350 0.441 HOMO/LUMO

350 0.365 HOMO/LUMO

λ [nm] f S2

306 0.114 HOMO−1/LUMO +1 296 0.126 HOMO−1/LUMO

328 0.105 HOMO−1/LUMO

λ [nm] f S3

4b 359 0.210 HOMO/LUMO +1 346 0.402 HOMO−1/ LUMO

306 0.230 HOMO−1/LUMO +1

a

TD-DFT calculations with Gaussian 03, revision E.1; B3LYP/631G(d) level of theory.15

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Figure 5. Frontier molecular orbital surfaces and energies for 5b, 6b, and 7b15

LUMO frontier orbitals are similar, wherein the electrons are delocalized in the dithienophosphole scaffold. The LUMO orbital displays a significant contribution from the phosphorus center as opposed to the HOMO orbital, also reflecting the typical phosphole σ*−π* orbital interaction.5 The LUMO+1 has contributions mainly in the naphthyl group as well as the phosphorus center (Figure 4). Factoring in the oscillator strength f, it was determined that the strongest transition is the HOMO/LUMO transition with a value of f = 0.365 (Table 3), which, according to their MOs, is essentially located in the dithienophosphole moiety. Moreover, other transitions such as HOMO-1/LUMO+1 ( f = 0.114, where the electron density is mainly shifted toward the naphthyl moiety) and HOMO-1/ LUMO (f = 0.105, where the electron density essentially shifts from the naphthyl to the dithienophosphole moiety) show relatively high f values, illustrating that the naphthyl moiety indeed contributes to the absorption of the system. For 4b, both its HOMO−1 and HOMO are quite similar, having contributions from the dithienophosphole and the pyrenyl group but none from the phosphorus center; the LUMO has distributions mainly in the pyrenyl region, and the LUMO+1 orbital has involvement mainly in the dithienophosphole region (Figure 4). In fact, LUMO+1 and LUMO have switched places, when compared to the corresponding orbitals for the phenyl derivative, as well as the naphthyl species, emphasizing the distinctly different electronics of the pyrenyl species. As for the oscillator strength, the transition from HOMO−1 to LUMO has the most prominent value of f (0.402), where the density de facto moves from the dithienophosphole (including the pyrenyl group) unit exclusively toward the pyrene unit (Table 3). More importantly, the contributions from both the dithienophosphole core and the pyrenyl unit in the HOMO orbital indicate that electronic communication between the two units exists. The pentavalent systems demonstrate similar behavior to the trivalent derivatives, wherein the HOMO−LUMO gap decreases from the naphthyl, to the phenanthryl, and finally to the pyrenyl congener (ΔEnaph = 3.75 > ΔEphen = 3.71 > ΔEpyr

= 3.65 eV). It is worth mentioning that both 5b and 6b have quite similar energy levels for HOMO−1 to LUMO+1 (EHOMO‑1 = −6.04 eV to ELUMO+1 = −1.35 eV for 5b, and EHOMO‑1 = −5.98 eV to ELUMO+1 = −1.29 eV for 6b), while 7b has narrower HOMO−1 to LUMO+1 values of EHOMO‑1 = −5.63 eV to ELUMO+1 = −1.82 eV with distinct differences in the electronic distributions of the orbitals again supporting the privileged electronic features of the latter system. The HOMO−1 and LUMO+1 orbitals of 5b are similar, mainly representing the naphthyl unit; the HOMO and LUMO orbitals are also very similar, mostly showing contribution in the dithienophosphole unit, illustrating the dithienophospholetypical distribution (Figure 5).5b Judging by the oscillator strength, it seems that only two main transitions have to be considered: HOMO/LUMO with f = 0.322 and HOMO−1/ LUMO+1 with f = 0.144 (Table 4). Table 4. Calculated Electronic Transitions and Relevant Oscillator Strengths (f) for 5b, 6b, and 7ba transition

5b

6b

λ [nm] f S1

377 0.322 HOMO/LUMO

385 0.226 HOMO/LUMO

λ [nm] f S2

290 0.144 HOMO−1/LUMO +1

325 0.128 HOMO/LUMO +1

7b 373 0.288 HOMO−1/ LUMO 348 0.307 HOMO/LUMO+1

a

TD-DFT calculations with Gaussian 03, revision E.1; B3LYP/631G(d) level of theory.15

Both these transitions suggest that excitation occurs only within the two respective D/A moieties without notable communication between them. The calculations clearly support the notion that this species is more closely related to its Pphenyl congener Ib-O. For the 6b system, the HOMO−1 involves mostly the phenanthryl group, with minor contribution from the 2431


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reluctance of these species to aggregate. Our studies clearly indicate the incorporation of an independent chromophore at the phosphorus center has a significant impact on the overall photophysical properties of the systems and thus provides important knowledge for further development of phosphorusbased π-conjugated chromophores.

dithienophosphole unit; the HOMO level mainly represents the dithienophosphole π-system, and the LUMO shows participation from both moieties, primarily from the dithienophosphole unit (π*-system) and some from the phenanthryl unit; LUMO+1 also displays contribution from the two units, but it is largely located at the phenanthryl moiety (Figure 5). Looking at its oscillator strength (Table 4), the transitions from HOMO to LUMO ( f = 0.226, where excitation occurs mainly within the dithienophosphole unit) and HOMO−1 to LUMO+1 ( f = 0.128, where excitation occurs mainly within the phenantryl unit) are of importance. In contrast to 5b, some degree of communication between the two subunits can be assumed on the basis of these calculations. Finally, in the 7b system, both HOMO−1 and HOMO show contribution from the dithienophosphole and the pyrenyl units, while the LUMO and LUMO+1 frontier orbitals predominantly spread over the dithienophosphole region (Figure 5). In terms of the oscillator strengths, two significant transitions have to be taken into account: from HOMO to LUMO+1 with a value of f = 0.307 and from HOMO−1 to LUMO with a value of f = 0.288, wherein both these transitions show that the excitation occurs from the whole unit toward the dithienophosphole acceptor unit (Table 4). The dynamic interaction between the orbitals of the two subchromophores clearly indicates the presence of significant electronic communication.

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EXPERIMENTAL SECTION

General Procedures. All manipulations were carried out under a dry nitrogen atmosphere employing standard Schlenk techniques. Solvents were dried using an MBraun solvent purification system. Unless noted otherwise, starting materials were used as received or distilled prior to use. Bis(diethylamino)chlorophosphane,16 3,3′dibromo-2,2′-dithiophene (1a),17 3,3′-dibromo-5,5′-bis(trimethylsilyl)2,2′-dithiophene (1b),18 and 3,3′-dibromo-5,5′-bis(tert-butyldimethylsilyl)-2,2′-dithiophene (1c)19 were prepared according to literature procedures. 31P{1H} NMR, 1H NMR, and 13C{1H} NMR were recorded on Bruker DRX400 and Avance (-II,-III) 400 MHz spectrometers. Chemical shifts were referenced to external 85% H3PO4 (31P) and external TMS (13C, 1H). Elemental analyses were performed in the Department of Chemistry at the University of Calgary. Mass spectra were run on a Finnigan SSQ 7000 spectrometer or a Bruker Daltonics AutoFlex III system. Crystal data and details of

Table 5. Crystallographic Data for 7a and 7b

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7a

CONCLUSIONS In conclusion, we have synthesized a series of new dithienophosphole species with increasing size of pendant PAH substituents ranging from two to four fused rings, as well as with a varying degree of steric bulk at the 2,6-position of the dithienophosphole scaffold. Our systematic investigations reveal that the naphthyl system is quite similar to the known P-phenyl relatives and the main scaffold dominates the photophysics. Upon increasing the size of the PAH substituent, its photophysical properties start to blend into the features of the main scaffold, which is particularly evident in the case of the pyrenyl-based systems, which show a symbiosis between the photophysics of the two subchromophores. The close proximity of the two units also allows for communication in the form of energy transfer with efficiencies of up to 87% between them. Furthermore these systems show uncharacteristically low (for dithienophospholes) photoluminescence quantum yields, which can also be attributed to the close proximity of the two chromophores. DFT calculations support the possibility of the electronic communication and the independent nature of the two subchromophores, particularly in the pyrenyl-based species, but the direction of the energy transfer from the PAH donor species to the dithienophosphole could not unequivocally be supported for all species by the calculations. However, the photophysical studies strongly suggest that the engery transfer occurs in the anticipated fashion. Despite the fact that the organization of the two pyrenyl-based species 7a and 7b in the solid state, as confirmed via X-ray crystallography, establishes the potential for intermolecular π-stacking, similar aggregation behavior in solution and in the corresponding amorphous solids could not be observed. This can be attributed to the polar nature of the new chromophores, which likely encounter strong solvation in the polar solvent media used for the studies, thereby preventing efficient aggregation in the presence of solvents. Even in the solid state, π-aggregation is observed only in the single cystals that were obtained through very slow evaporation of the solvent, which further suggests the

formula Mr T/K cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z, Dc/Mg cm−3 F(000) μ(Mo Kα)/mm−1 θ range for data collection/deg reflns collected/unique (Rint) data/restraints/params final R indices [I > 2σ(I)] R indices (all data) GOF on F2 largest diff peak and hole/e Å3

7b

C24H13OPS2 412.43 173(2) triclinic P1̅ 8.0690(3) 10.1130(4) 11.9800(4) 81.033(2) 87.225(2) 68.423(2) 897.93(6) 2, 1.525 424 0.399 2.19 to 27.52

C30H29OPS2Si2 556.80 173(2) triclinic P1̅ 9.9490(2) 11.7360(3) 14.7530(4) 71.3030(10) 74.483(2) 65.750(2) 1469.18(6) 2, 1.259 584 0.339 1.96 to 27.50

7479/4080 [R(int) = 0.0292] 4080/0/253 R1 = 0.0474, wR2 = 0.1349 R1 = 0.0560, wR2 = 0.1468 1.216 0.551 and −0.633

12420/6680 [R(int) = 0.0334] 6680/0/325 R1 = 0.0540, wR2 = 0.1331 R1 = 0.0731, wR2 = 0.1565 1.138 0.367 and −0.436

the data collection are provided in Table 5 and the Supporting Information cif files. Diffraction data were collected on a Nonius Kappa CCD diffractometer, using Mo Kα radiation (λ) 0.71073 Å (graphite monochromator). The structures were solved by direct methods (SHELXTL) and refined on F2 by full-matrix least-squares techniques. All fluorescence experiments were recorded in dichloromethane solution on a Jasco FP-6600 spectrofluorometer and UV− vis−NIR Cary 5000 spectrophotometer. Dichloro(naphthalen-1-yl)phosphane (A). To a stirred solution of 1-naphthylmagnesium bromide [obtained from l-bromonaphthalene (4.14 g, 20.0 mmol) and magnesium (0.98 g, 40.0 mmol) in dry THF 2432


Organometallics

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JHH = 8.0 Hz, 1H), 7.81 (3JHH, J = 8.0 Hz, 1H), 7.68 (m, 1H), 7.58 (m, 1H), 7.29 (m, 1H), 7.27 (s, 2H), 7.24 (m, 1H), 0.32 (s, SiMe3, 18H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 148.2 (d, JCP = 9.5 Hz), 146.9 (s), 142.9 (d, JCP = 4.2 Hz), 136.1 (d, JCP = 22.7 Hz), 134.9 (s), 134.0 (d, JCP = 4.8 Hz), 133.8 (d, JCP = 17.4 Hz), 130.0 (s), 129.5 (d, JCP = 2.2 Hz), 129.2 (d, JCP = 1.7 Hz), 126.6 (d, JCP = 1.9 Hz), 126.4 (d, JCP = 10.6 Hz), 126.1 (d, JCP = 2.9 Hz), 126.0 (all aromatics), 0.2 (s, SiMe3) ppm. HRMS (EI, 70 eV): m/z calcd for C24H27PS2Si2 ([M+]) 466.0830; found 466.0833. 4-(Pyren-1-yl)-4H-phospholo[3,2-b:4,5-b′]dithiophene, 4a. Following the same reaction conditions as described in the synthesis of 2b, we used 1a (0.85 g, 2.6 mmol), C (0.80 g, 2.6 mmol), excess TMEDA (0.75 mL, 5.0 mmol), and nBuLi (2.1 mL, 5.2 mmol, 2.5 M in hexane) in dry diethyl ether (150 mL). The solvent was removed under vacuum, and the residue was filtered over neutral alumina using a diethyl ether wash. The product solution was evaporated to dryness, washed with diethyl ether again, and recrystallized with a CH2Cl2/ pentane mixture to obtain 4a as clear, light yellow crystals (yield 0.39 g, 57%). 31P{1H} NMR (162 MHz, CDCl3): δ −28.5 ppm (s);. 1H NMR (400 MHz, CDCl3): δ 9.21 (dd, 3JHH = 9.2 Hz, 3JHP = 5.4 Hz, 1H), 8.30 (d, 3JHH = 9.2 Hz, 1H), 8.29 (dd, 3JHH = 7.6 Hz, 4JHH = 1.0 Hz, 1H), 8.22 (dd, 3JHH = 7.7 Hz, 4JHH = 1.0 Hz, 1H), 8.07 (m, 2H), 7.94 (m, 2H), 7.58 (dd, 3JHH = 7.9 Hz, 3JHP = 5.4 Hz, 1H), 7.30 (dd, 3 JHH = 4.9 Hz, 4JHP = 2.6 Hz, 2H), 7.24 (d, 3JHH = 5.6 Hz, 2H) ppm. 13 C{1H} NMR (100 MHz, CDCl3): δ 149.2 (d, JCP = 11.8 Hz), 146.8 (s), 141.6 (d, JCP = 13.4 Hz), 139.5 (s), 135.3 (s), 134.8 (s), 134.2 (s), 132.9 (d, JCP = 25.3 Hz), 131.8 (s), 131.3 (d, JCP = 2.1 Hz), 128.6 (d, JCP = 18.8 Hz), 128.5 (s), 128.0 (s), 127.6 (d, JCP = 2.4 Hz), 127.2 (d, JCP = 19.2 Hz), 126.5 (d, JCP = 6.2 Hz), 126.2 (s), 125.8 (d, JCP = 12.2 Hz), 125.5 (s), 125.1 (d, JCP = 2.4 Hz) (all aromatics) ppm. HRMS (EI, 70 eV): m/z calcd for C24H13PS2 ([M+]) 396.0196; found 396.0197. 2,6-Bis(tert-butyldimethyl)4-(pyren-1-yl)-4H-phospholo[3,2b:4,5-b′]dithiophene, 4c. Following the same reaction conditions as described in the synthesis of 2b, we used 1c (0.78 g, 1.4 mmol), C (0.43 g, 1.4 mmol), excess TMEDA (0.45 mL, 3.0 mmol), and nBuLi (1.1 mL, 2.8 mmol, 2.5 M in hexane) in dry diethyl ether (100 mL). The solvent was removed under vacuum, and the residue was filtered over neutral alumina using a pentane wash. The product solution was evaporated to dryness and washed with pentane, and 4c was obtained as a light white-yellow solid (yield 0.59 g, 68%). 31P{1H} NMR (162 MHz, CDCl3): δ −33.5 ppm (s). 1H NMR (400 MHz, CDCl3): δ 9.25 (dd, 3JHH = 5.6 Hz, 3JHP = 3.8 Hz, 1H), 8.26 (m, 3H), 8.01 (m br, 4H), 7.56 (m, 1H), 7.28 (s, 2H), 0.92 (s, SitBu, 18H), 0.28 (s, SiMe2, 6H), 0.26 (s, SiMe2, 6H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 148.7 (d, JCP = 12.0 Hz), 147.2 (s), 141.3 (d, JCP = 13.2 Hz), 139.2 (s), 135.1 (s), 134.9 (s), 134.0 (s), 132.8 (d, JCP = 24.9 Hz), 131.5 (s), 131.1 (d, JCP = 1.1 Hz), 128.7 (d, JCP = 19.5 Hz), 128.6 (s), 128.2 (s), 127.6 (d, JCP = 2.2 Hz), 127.2 (d, JCP = 18.9 Hz), 126.6 (d, JCP = 6.3 Hz), 126.4 (s), 125.9 (d, JCP = 11.6 Hz), 125.5 (s), 125.3 (d, JCP = 2.9 Hz) (all aromatics), 31.1 (s, SitBu), 22.6 (s, SitBu), 1.2 (s, SiMe2) ppm. HRMS (EI, 70 eV): m/z calcd for C36H41PS2Si2([M+]) 624.1926; found 624.1906. Anal. Calcd (%) for C36H41PS2Si2: C 69.18, H 6.61. Found: C 68.23, H 6.62. 4-(Naphthalen-1-yl)-2,6-bis(trimethylsilyl)-4H-phospholo[3,2-b:4,5-b′]dithiophene 4-Oxide, 5b. To a solution of 2b (0.8 g, 1.7 mmol) in CHCl3 (70 mL) was added an excess of H2O2 (30%, 2 mL), and the solution was stirred for 16 h at room temperature. Subsequently, the solution was dried with MgSO4 and all volatile materials were removed under vacuum. The residue was purified by column chromatography (SiO2, hexane/ethyl acetate, 1:1) to obtain a pale yellow solid (yield 0.6 g, 73%). 31P{1H} NMR (162 MHz, CDCl3): δ 21.3 ppm (s). 1H NMR (400 MHz, CDCl3): δ 8.96 (d, 3JHH = 8.5 Hz, 1H), 8.04 (d, 3JHH = 8.4 Hz, 1H), 7.94 (d, 3JHH = 8.2 Hz, 1H), 7.85 (ddd, 3JHP = 8.3 Hz, 3JHH = 7.1 Hz, 4JHH = 1.2, 1H), 7.69 (m, 1H), 7.60 (m, 1H), 7.42 (m, 1H), 7.36 (d, 3JHP = 2.1 Hz, 2H), 0.32 (s, SiMe3, 18H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 150.6, 145.8 (d, JCP = 10.7 Hz), 145.1 (d, JCP = 20.3 Hz), 141.4(s), 140.3(s), 133.8 (d, JCP = 3.0 Hz), 133.0 (d, JCP = 12.8 Hz), 131.1 (d, JCP = 7.0 Hz), 131.0 (s), 129.4 (s), 128.3 (s), 127.9 (d, JCP = 102.3 Hz), 126.7 (d, JCP

(100 mL)] was added bis(diethylamino)chlorophosphane (4.21 g, 20.0 mmol) in dry diethyl ether (20 mL) dropwise at 0 °C. The solution was warmed to room temperature and left for 16 h. HCl (40 mL, 80.0 mmol, 2 M in diethyl ether) was added slowly to the reaction mixture at 0 °C and left stirring for 30 min. The white diethylammonium chloride precipitate was separated using a cannula with diethyl ether wash, and the solution was evaporated to afford a white solid (yield: 3.30 g, 72%). 31P{1H} NMR (162 MHz, CDCl3): δ 163.8 ppm (s). 1H NMR (400 MHz, CDCl3): δ 8.64 (d, 3JHH = 7.5 Hz, 1H), 8.27 (m, 1H), 8.07 (d, 3JHH = 8.1 Hz, 1H), 7.96 (d, 3JHH = 8.0 Hz, 1H), 7.66 (m, 3H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 135.5 (d, JCP = 60.1 Hz), 134.2 (s), 134.1 (d, JCP = 2.3 Hz), 132.4 (d, JCP = 19.0 Hz), 131.1 (d, JCP = 32.0 Hz), 129.4 (s), 127.8 (d, JCP = 2.3 Hz), 127.1 (s), 125.5 (d, JCP = 9.1 Hz), 124.8 (d, JCP = 23.8 Hz) (all aromatics) ppm. MS (ESI): m/z 229 [M+], 191 [M+ − Cl]. Dichloro(phenanthren-9-yl)phosphane (B). Following the same reaction conditions as described in the synthesis above, 9phenanthrylmagnesium bromide [obtained from 9-bromophenanthrene (2.57 g, 10.0 mmol) and magnesium (0.49 g, 20.0 mmol) in dry THF (50 mL)] and bis(diethylamino)chlorophosphane (2.11 g, 10.0 mmol) in dry diethyl ether (20 mL) were used. The solution was warmed to room temperature and left stirring for 16 h. HCl (20 mL, 40.0 mmol, 2 M in diethyl ether) was added slowly to the reaction mixture at 0 °C and left stirring for 30 min. The diethylammonium chloride precipitate was separated using a cannula with diethyl ether wash, and the solution was evaporated to afford a light yellow solid (yield: 1.95 g, 70%). 31P{1H} NMR (162 MHz, CDCl3): δ 163.3 ppm (s). 1H NMR (400 MHz, CDCl3): δ 8.85 (m, 3H), 8.54 (m, 1H), 8.03 (d, 3JHH = 7.9 Hz, 1H), 7.74 (m br, 4H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 144.2 (s), 134.3 (d, JCP = 42.3 Hz), 132.6 (s), 132.2 (s), 130.6 (d, JCP = 14.9 Hz), 130.4 (d, JCP = 66.5 Hz), 128.8 (s), 127.7 (d, JCP = 7.2 Hz), 127.3 (s), 127.1 (s), 126.7 (s), 126.2 (d, JCP = 20.3 Hz), 123.8 (s), 122.9 (d, JCP = 10.4 Hz) (all aromatics) ppm. MS (ESI): m/z 280 [M+]. Dichloro(pyren-1-yl)phosphane (C). nBuLi (7.8 mL, 19.5 mmol, 2.5 M in hexane) was added dropwise to a solution of dry THF/ diethyl ether (80 mL) at −78 °C, and subsequently, 1-bromopyrene (5.47 g, 19.5 mmol), dissolved in a THF/diethyl ether mixture (40 mL), was slowly added at the same temperature. The reaction mixture was left stirring for 30 min at that temperature before warming to 10 °C and left stirring for another 20 min. The suspension was cooled back to −78 °C, before adding bis(diethylamino)chlorophosphane (4.10 g, 19.5 mmol) diluted in a THF/diethyl ether mixture (20 mL) and left stirring at room temperature for 16 h. HCl (40 mL, 80.0 mmol, 2 M in diethyl ether) was added slowly to the reaction mixture at −78 °C and stirred for 30 min at room temperature. The diethylammonium chloride precipitate was separated using a cannula with diethyl ether wash, and the solution was evaporated to afford a bright yellow solid (yield: 4.90 g, 83%). 31P{1H} NMR (162 MHz, CDCl3): δ 165.1 ppm (s). 1H NMR (400 MHz, CDCl3): δ 8.86 (dd, 3 JHH = 9.2 Hz, 4JHP = 3.0 Hz, 1H), 8.79 (dd, 3JHH = 8.0 Hz, 3JHP = 7.0 Hz, 1H), 8.27 (m, 5H), 8.11 (m, 2H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 134.8 (s), 132.3 (s), 131.4 (s), 130.5 (s), 130.4 (s), 129.4 (d, JCP = 3.8 Hz), 128.6 (d, JCP = 15.7 Hz), 127.6 (s), 127.4 (s), 126.9 (s), 126.9 (d, JCP = 3.2 Hz), 126.1 (s), 125.4 (d, JCP = 4.6 Hz), 125.2 (s), 124.5 (s), 123.2 (d, JCP = 34.2 Hz) (all aromatics) ppm. MS (ESI): m/z 303 [M+], 264 [M+ − Cl]. 4-(Naphthalen-1-yl)-2,6-bis(trimethylsilyl)-4H-phospholo[3,2-b:4,5-b′]dithiophene, 2b. To a solution of 1b (1.86 g, 4.0 mmol) and excess TMEDA (1.5 mL, 10 mmol) in dry diethyl ether (200 mL) was added nBuLi (3.2 mL, 8.0 mmol, 2.5 M in hexane) dropwise at −78 °C. Subsequently, A (1.20 g, 4.0 mmol) dissolved in diethyl ether (15 mL) was added slowly to the reaction mixture, and the resulting mixture was allowed to warm quickly to room temperature. The solvent was then removed under vacuum, and the residue was filtered over neutral alumina using a pentane wash. The solution was evaporated to dryness, the solid was washed with pentane, and 2b was obtained as a light yellow solid (yield 1.2 g, 64%). 31 1 P{ H} NMR (162 MHz, CDCl3): δ −30.9 ppm (s). 1H NMR (400 MHz, CDCl3): δ 8.87 (dd, 3JHH = 5.6 Hz, 3JHP = 2.8 Hz, 1H), 7.90 (d, 2433


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= 5.9 Hz), 125.0 (d, JCP = 15.1 Hz) (all aromatics), 0.4 (s, SiMe3) ppm. HRMS (EI, 70 eV): m/z calcd for C24H27OPS2Si2 ([M+]) 482.0779; found 482.0769. 4-(Phenanthren-9-yl)-2,6-bis(trimethylsilyl)-4H-phospholo[3,2-b:4,5-b′]dithiophene 4-Oxide, 6b. The trivalent species 3b could not be obtained purely, so it was oxidized directly to 6b. Following the same reaction conditions as described in the synthesis of 2b and 5b, we used 3b (0.48 g, 0.9 mmol) [obtained from 1b (0.69 g, 1.5 mmol), B (0.49 g, 1.5 mmol), excess TMEDA (0.5 mL, 3.4 mmol), and nBuLi (1.2 mL, 2.9 mmol, 2.5 M in hexane) in dry THF (50 mL)] and excess H2O2 (30%, 2 mL) in CHCl3 (70 mL). The solution was dried with MgSO4, and all volatile materials were removed under vacuum. The residue was purified by column chromatography (SiO2, hexane/ethyl acetate, 1:1) to obtain a light yellow solid (yield 0.3 g, 63%). 31P{1H} NMR (162 MHz, CDCl3): δ 21.0 ppm (s). 1H NMR (400 MHz, CDCl3): δ 8.93 (m, 1H), 8.74 (m, 1H), 8.67 (d, J = 8.1 Hz, 1H), 8.29 (d, 3JHP = 18.7 Hz, 1H), 7.83 (m, 1H), 7.73 (m, 3H), 7.59 (m, 1H), 7.39 (d, 3JHP = 2.0 Hz, 2H), 0.32 (s, SiMe3, 18H) ppm. 13 C{1H} NMR (100 MHz, CDCl3): δ 150.9 (d, JCP = 24.9 Hz), 145.8 (d, JCP = 10.8 Hz), 141.2 (d, JCP = 109.0 Hz), 134.1 (d, JCP = 11.7 Hz), 133.0 (d, JCP = 12.8 Hz), 132.5 (s), 131.2 (d, JCP = 10.1 Hz), 130.8 (d, JCP = 9.0 Hz), 130.2 (s), 130.1 (s), 130.0 (s), 129.3 (s), 127.6 (d, JCP = 16.7 Hz), 127.4 (d, JCP = 5.6 Hz), 127.2 (s), 127.1 (s), 126.0 (s), 123.5 (d, JCP = 74.2 Hz) (all aromatics), 0.02 (s, SiMe3) ppm. HRMS (EI, 70 eV): m/z calcd for C28H29OPS2Si2 ([M+]) 532.0936; found 532.0922. 4-(Pyren-1-yl)-4H-phospholo[3,2-b:4,5-b′]dithiophene 4Oxide, 7a. Following the same reaction conditions as described in the synthesis of 2b, we used 4a (0.35 g, 0.9 mmol) and excess H2O2 (30%, 2 mL) in CHCl3 (50 mL). The solution was dried with MgSO4, and all volatile materials were removed under vacuum. The residue was recrystallized with a minimal amount of CH2Cl2 to obtain clear yellow crystals (yield 0.27 g, 84%). 31P{1H} NMR (162 MHz, CDCl3): δ 23.3 ppm (s). 1H NMR (400 MHz, CDCl3): δ 9.33 (d, 3JHH = 9.2 Hz, 1H), 8.35 (t, 3JHH = 9.8 Hz, 2H), 8.27 (d, 3JHH = 7.5 Hz, 1H), 8.11 (m br, 5H), 7.41 (dd, 3JHH = 4.9 Hz, 4JHP = 2.2 Hz, 2H), 7.32 (dd, 3JHH = 4.9 Hz, 3JHP = 3.3 Hz, 2H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 146.6 (d, JCP = 46.0 Hz), 143.6 (s), 141.5 (d, JCP = 54.5 Hz), 140.1 (s), 135.1 (s), 132.1 (s), 131.3 (d, JCP = 12.4 Hz), 130.7 (s), 130.1 (d, JCP = 25.0 Hz), 129.0 (s), 128.9 (s), 128.6 (d, JCP = 3.3 Hz), 128.4 (d, JCP = 1.7 Hz), 127.3 (s), 126.9 (d, JCP = 7.8 Hz), 126.7 (d, JCP = 10.7 Hz), 125.5 (d, JCP = 6.8 Hz), 125.3 (s), 124.5 (d, JCP = 2.0 Hz), 124.3 (s) (all aromatics) ppm. HRMS (EI, 70 eV): m/z calcd for C24H13OPS2 ([M+]) 412.0145; found 412.0132. Anal. Calcd (%) for C24H13OPS2: C 69.89, H 3.18. Found: C 69.16, H 3.07. 4-(Pyren-1-yl)-2,6-bis(trimethylsilyl)-4H-phospholo[3,2b:4,5-b′]dithiophene 4-Oxide, 7b. The trivalent species 4b could not be obtained purely, so it was oxidized directly to 7b. Following the same reaction conditions as described in the synthesis of 6b we used 4b (0.49 g, 0.9 mmol) [obtained from 1b (0.66 g, 1.4 mmol), C (0.43 g, 1.4 mmol), excess TMEDA (0.45 mL, 3.0 mmol), and nBuLi (1.1 mL, 2.8 mmol, 2.5 M in hexane) in dry THF (100 mL)] and excess H2O2 (30%, 2 mL) in CHCl3 (70 mL). The solution was dried with MgSO4, and all volatile materials were removed under vacuum. The residue was purified by column chromatography (SiO2, hexane/ethyl acetate, 1:1) and recrystallized with a minimal amount of acetone to obtain yellow crystals (yield 0.25 g, 50%). 31P{1H} NMR (162 MHz, CDCl3): δ 21.9 ppm (s). 1H NMR (400 MHz, CDCl3): δ 9.33 (d, J = 9.3 Hz, 1H), 8.34 (m, 2H), 8.23 (m, 3H), 8.08 (m, 3H), 7.42 (d, 3JHP = 2.0 Hz, 2H), 0.31 (s, SiMe3,18H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 149.8 (d, JCP = 28.6 Hz), 143.5 (d, JCP = 9.8 Hz), 141.2 (d, JCP = 96.4 Hz), 136.4 (s), 134.9 (s), 134.6 (s), 134.2 (s), 134.0 (d, JCP = 14.3 Hz), 132.2 (d, JCP = 49.1 Hz), 130.5 (d, JCP = 43.4 Hz), 129.2 (d, JCP = 15.5 Hz), 128.7 (s), 126.6 (s), 126.1 (s), 125.3 (d, JCP = 7.5 Hz), 125.0 (d, JCP = 12.5 Hz), 124.7 (s), 124.4 (s), 124.2 (d, JCP = 15.5 Hz), 123.2 (all aromatics), −0.3 (s, SiMe3) ppm. HRMS (EI, 70 eV): m/z calcd for C30H29OPS2Si2 ([M+]) 556.0936; found 556.0931. Anal. Calcd (%) for C30H29OPS2Si2: C 64.71, H 5.25. Found: C 63.70, H 5.15. 2,6-Bis(tert-butyldimethyl)4-(pyren-1-yl)-4H-phospholo[3,2b:4,5-b′]dithiophene 4-Oxide, 7c. Following the same reaction

conditions as described in the synthesis of 5b we used 4a (0.48 g, 0.8 mmol) and excess H2O2 (30%, 2 mL) in CHCl3 (50 mL). The solution was dried with MgSO4, and all volatile materials were removed under vacuum. The residue was recrystallized with a minimal amount of acetone to obtain clear yellow crystals (yield 0.27 g, 55%). 31 1 P{ H} NMR (162 MHz, CDCl3): δ 22.3 ppm (s). 1H NMR (400 MHz, CDCl3): δ 9.28 (d, 3JHH = 9.1 Hz, 1H), 8.26 (m br, 5H), 8.08 (m 3H), 7.43 (d, 3JHP = 2.0 Hz, 2H), 0.89 (s, SitBu,18H), 0.28 (s, SiMe2, 6H), 0.27 (s, SiMe2, 6H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 150.9 (d, JCP = 24.5 Hz), 143.0 (d, JCP = 10.9 Hz), 141.9 (d, JCP = 108.7 Hz), 136.1 (s), 134.9 (s), 134.8 (s), 134.7 (s), 134.0 (d, JCP = 12.9 Hz), 131.3 (d, JCP = 52.0 Hz), 130.0 (d, JCP = 40.7 Hz), 129.0 (d, JCP = 13.0 Hz), 127.4 (s), 126.7 (s), 126.5 (s), 125.6 (d, JCP = 6.6 Hz), 125.3 (d, JCP = 11.0 Hz), 125.1 (s), 124.5 (d, JCP = 30.9 Hz), 124.5 (d, JCP = 14.3 Hz), 123.1 (s) (all aromatics), 26.5 (s, SitBu), 17.1 (s, SitBu), −4.7 (s, SiMe), −4.8 (s, SiMe) ppm. HRMS (EI, 70 eV): m/z calcd for C36H41OPS2Si2 ([M+]) 640.1875; found 640.1906. Anal. Calcd (%) for C36H41OPS2Si2: C 67.46, H 6.45. Found: C 67.28, H 6.39. 2,6-Bis(tert-butyldimethyl)-4-methyl-4-(pyren-1-yl)-4Hphospholo[3,2-b:4,5-b′]dithiophen-4-ium Triflate, 8. Methyl triflate (0.33 g, 2.0 mmol) was added dropwise to a solution of 4c (0.96 g, 1.5 mmol) in CH2Cl2 (90 mL) at 0 °C. The solution was kept stirring for 2 h before raising the temperature to room temperature. Subsequently, the solvent was removed under vacuum, and the residue was washed twice with small amounts of diethyl ether and acetone, respectively. After recrystallization with a CHCl3/pentane mixture, 8 was obtained as clear yellow crystals (yield 0.72 g, 74%). 31P{1H} NMR (162 MHz, CDCl3): δ 7.9 ppm (s). 1H NMR (400 MHz, CDCl3): δ 8.77 (dd, 3JHP = 16.5 Hz, 3JHH = 8.2 Hz, 1H), 8.45 (dd, 3JHH = 8.2 Hz, 4JHH = 2.9 Hz, 1H), 8.33 (t, 3JHH = 7.7 Hz, 2H), 8.25 (m, 2H), 8.11 (m, 2H), 7.97 (d, 3JHH = 9.2 Hz, 1H), 7.67 (d, 3JHP = 1.9 Hz, 2H), 3.08 (d, 2JHP = 14.3 Hz, P-Me, 3H), 0.92 (s, SitBu, 18H), 0.34 (s, SiMe2, 6H), 0.33 (s, SiMe2, 6H) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ 153.1 (d, JCP = 22.0 Hz), 147.4 (d, JCP = 11.3 Hz), 138.1 (s), 137.1 (s), 134.6 (d, JCP = 13.8 Hz), 134.0 (d, JCP = 10.0 Hz), 132.8 (d, JCP = 12.9 Hz), 131.9 (d, JCP = 5.6 Hz), 131.8 (s), 131.1 (d, JCP = 30.7 Hz), 130.1 (s), 128.4 (s), 128.2 (d, JCP = 11.7 Hz), 127.4 (s), 126.0 (d, JCP = 15.2 Hz), 125.1 (s), 125.0 (s), 123.9 (s), 122.4 (s), 122.2 (d, JCP = 9.1 Hz) (all aromatics), 26.4 (s, SitBu), 17.0 (s, SitBu), 10.4 (d, JCP = 55.0 Hz, P-Me), −4.87 (s, SiMe), −4.91 (s, SiMe) ppm. HRMS (EI, 70 eV): m/z calcd for C34H35F3O3PS3Si2 ([M+ − C4H9]) 731.0977; found 731.0950. Anal. Calcd (%) for C38H44F3O3PS3Si2: C 57.84, H 5.62. Found: C 57.92, H 5.39.

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ASSOCIATED CONTENT

S Supporting Information *

Photophysical data of concentration-dependent studies, qualitative solid-state organization of 7c, and crystallographic information files (CIF) for 7a and 7b. This material is available free of charge via the Internet at http://pubs.acs.org. The CIF files were also deposited with the Cambridge Crystallographic Data Centre (CCDC), and CCDC codes 863382 and 863383 were allocated. These data are available without cost at www. ccdc.cam.ac.uk/conts/retrieving.html or from the CCDC, 12 Union Road, Cambridge CB2 IEZ, U.K.; fax: +44(0)1223336033; e-mail: [email protected].

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by NSERC of Canada and the Canada Foundation for Innovation (CFI) is gratefully acknowledged. 2434


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C.J.C. thanks the University of Calgary for an Open Scholarship. We also thank Alberta Ingenuity now part of Alberta Innovates−Technology Futures for a New Faculty Award (T.B.) and a graduate scholarship (Y.R.), as well as Talisman Energy for a graduate scholarship (Y.R.).

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