Electron Transfer and Aggregate Formation Coinduced Emission

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Electron Transfer and Aggregate Formation Coinduced Emission Enhancement of 9-Cycloheptatrienylidene Fluorenes in the Presence of Cupric Chloride Qingchuan Han, Qiang Su, Lei Tang, Jinwu Feng, Ping Lu,* and Yanguang Wang* Chemistry Department, Zhejiang UniVersity, Hangzhou 310027, P. R. China ReceiVed: July 21, 2010; ReVised Manuscript ReceiVed: September 18, 2010

A series of 2,7-diaryl-9-cycloheptatrienylidene fluorenes (9-CHFs) were synthesized, and their structures were confirmed by spectroscopic methods. By cooperation with cupric chloride in tetrahydrofuran, 9-CHFs exhibited emission enhancement at locally excited (LE) band and aggregation induced emission at lower energy band when the solution was excited at two different wavelengths. By kinetically tracking the process via absorption, emission, dynamic light scattering, and TEM photography, it could be concluded that electron transfer from 9-CHFs to cupric cation and the aggregate formation coinduced the turn-on luminescence. Based on the study of the fluorescent structure-property relationship, the investigation of anion effect, and the analysis of X-ray diffraction, it was revealed that electrostatic interactions and intermolecular C-H...π interactions resulted in aggregates formation and thereafter restricted the intramolecular free rotation of σ-bonds, which finally increased the quantum yields at two bands. Thus, emission efficiencies of 9 and cupric chloride in THF solution were determined to be 0.55 and 0.48 for LE band emission and lower energy band emission, respectively. Introduction Organic compounds with luminescent properties have practical uses in many fields, such as organic light emitting diodes (OLEDs)1 and fluorescent diagnostic kits.2 In most cases, emission efficiency of a compound in the solid state is lower than that in its solution due to the intermolecular interactions and the corresponding nonradiative decay. This phenomenon is named aggregation-causing quenching (ACQ)3 but runs in the opposite direction to its practical application because the real state fabricated in most kinds of devices would be the solid state. In order to overcome this drawback, many efforts have been made to seek molecules with particular structures which could emit intense light in aggregate states.4 Fortunately, quite a few structures have been revealed to possess this character, which is subsequently called aggregation-induced emission enhancement (AIEE) and/or aggregation induced emission (AIE) observed by Swager,5 Park,6 and Tang7 at the beginning of the 21st century. Along with more structures with AIEE/AIE character being recognized,8,9 restricted intramolecular rotation7,10 has been ascribed as the key factor causing these phenomena. Several techniques have thereafter been efficiently developed to restrict the free rotation of the molecule to evaluate AIEE/ AIE or apply AIEE/AIE in biological detection,11 for example, adding water to induce nanoparticle formation, increasing the viscosity of the solvent, lowering the temperature to form a glassy solid, increasing the pressure on the matrix surface, doping the compound in polymer matrix, as well as embedding the compound in micella or vesicle.7–10,12 By extension of our previous work on AIEE,9 here we would like to report the electron transfer and aggregate formation coinduced emission enhancement of 9-cycloheptatrienylidene fluorenes (9-CHFs) in the presence of cupric chloride and their conformational effects on the emission spectra. * To whom correspondence should be addressed. Fax/Tel.: +86-57187952543. E-mail: [email protected] (P.L.); [email protected] (Y.W.).

Results and Discussion 1. Synthesis. Structures of compounds 1-15 are shown in Scheme 1. Synthetic routes to 1-9 are presented in Scheme S1 in the Supporting Information, while synthetic routes to 10-15 are drawn in Scheme S2. Suzuki coupling and Sonogashira coupling were used to construct these molecules in moderate to good yields. All synthesized compounds were fully characterized and confirmed by 1H NMR, 13C NMR, and high-resolution mass spectroscopy (HRMS) (Figure S16). 2. Absorption and Emission Measurements. Compounds 1-15 are soluble in tetrahydrofuran (THF). Photoabsorptive and photoemissive spectra are normally measured in a concentration of 1 × 10-5 M in THF. 3. Photophysical Properties of 1 with Addition of CuCl2. The absorption spectrum of 1 in THF solution showed absorption bands in the range of 250-450 nm with a maximum absorption wavelength centered at 392 nm, while the emission spectrum of 1 showed an emission band at 377 nm, which could be assigned to locally excited emission (LE), when excited at 324 nm. The quantum yield of this LE band was determined to be 0.004 because of its self-absorption. Therefore, the lifetime of 1 in THF was not detectable. After addition of 0.5 equiv CuCl2 to a THF solution of 1 for a period of time, absorption spectra dropped obviously at the range of 250-300 nm and showed the most significant reduction of the band at 392 nm (Figure 1A) as the solution was bleached. Meanwhile, dramatic increment of the LE band could be observed when the solution was excited at 324 nm (Figure 1B). Addition of CuCl2, which resulted in the electron transfer from the 9-CHF core of 1 to Cu2+, interrupted the conjugation of 1, directly diminishing the self-absorption and lighting up LE emission. To our surprise, a new emission at lower energy band (458 nm) occurred and gradually reached a 0.19 quantum yield as the time was prolonged when the solution was excited at 372 nm (Figure 1C). Lifetimes of these two bands were determined to be 1.09 and 2.02 ns, respectively, based on one-

10.1021/jp1068126  2010 American Chemical Society Published on Web 10/12/2010

Electron Transfer and AIEE of 9-CHFs

J. Phys. Chem. C, Vol. 114, No. 43, 2010 18703

SCHEME 1: Structures of Compounds 1-15

component fit (Figure 1D).13 Job’s plot was employed to determine the ratio between 9-CHFs and CuCl2. Keeping the total molar concentration of CuCl2 and 9-CHFs at 1 × 10-5 mol L-1 and varying their molar fractions from 1/9 to 9/1, emissions were measured. The ratio of 9-CHFs to CuCl2 was found to be 2:1 (Figure S1). In order to scrutinize this transformation dynamically, time dependent emission spectra were drawn (Figure 2). First, fluorescent intensity had a plateau for a few minutes without obvious increment for both LE emission (Figure 2A) and lower energy band emission (Figure 2C). Then, a significant mutation was observed with dramatic emission enhancement. Finally, a second plateau approached. Rate constants for LE emission enhancement (Figure 2B) and lower energy band emission enhancement (Figure 2D) were calculated to be 0.21 and 0.17 min-1 according to the equation,14 respectively. Both increments showed first-order kinetics no matter how many excess amounts of CuCl2 (0.5-5 equiv) were added. The fluorescent turn-on at 458 nm occurred 0.5-1 min later than LE emission started to increase. Significantly absorptive reduction at 392 nm and dramatically emissive enhancement at 377 nm were similar to our previous observation of compound 515 when 5 was acidified with sulfuric acid. However, turn-on emission at lower energy band (458 nm) was not detected when either 1 or 5 was acidified. By photographing the THF solution of 1 and 0.5 equiv CuCl2 after standing at room temperature for 2 h, aggregates were detected

(Figure 1E). Emission at lower energy band might be the formation of aggregates which emitted intense light with sky blue. 4. Working Mechanism between 1 and CuCl2. In order to understand how 1 reacted with CuCl2, we synthesized 2-4 for mechanism study. Without the conjugation between five-member and seven-member rings, 2 did not react with CuCl2 at all. Both absorption and emission spectra of 2 remained the same before and after the addition of CuCl2 (Figure S2). Compound 3, with the 9-CHF core, could be used as a UV-vis pH sensor16 as in our previous report. With the addition of CuCl2 into the THF solution of 3, significantly decreased absorption at 379 nm was detected (Figure S3), which was similar to its addition with acid.16 However, no emission was observed for 3 before and after addition of Cu2+. Oxidative coupling of 1 afforded 4 in 80% yield (Scheme S1). Both 1 and 4 could transfer electrons from the 9-CHF core to Cu2+ as well as form aggregates after the solution stood for a period of time. The difference was that the free rotation of biphenyl in 4 was completely “locked” due to its rigid skeleton. In other words, there would be no dihedral angle change before and after aggregates formed.10b 4 absorbed light at 406 nm and emitted vibrational structures (LE bands) at 379 and 399 nm with quantum yield of 0.02. Addition of CuCl2 resulted in the absorptive deduction at 406 nm (Figure 3A) and the LE emissive enhancement, which was magnified to 34-fold of its initial value (Figure 3B and Figure S4). However, emission from the lower energy band was not detected

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Figure 1. (A) Absorption of 1 in THF after addition of 0.5 equiv CuCl2; the inset is the absorption-time profile at 392 nm. (B) Emission accordingly excited at 324 nm. (C) Emission accordingly excited at 372 nm. (D) Time-resolved fluorescence spectra at low bands after keeping the mixture of 1 and 0.5 equiv CuCl2 at room temperature for 2 h. (E) TEM and fluorescent images (under 365 nm) after keeping the mixture of 1 and 0.5 equiv CuCl2 at room temperature for 2 h.

Figure 2. (A) Fluorescence-time profile of 1 in THF associated with various equivalents of CuCl2, emission at 377 nm. (B) Experimental rate constant, emission at 377 nm. (C) Fluorescence-time profile of 1 in THF associated with various equivalents of CuCl2, emission at 458 nm. (D) Experimental rate constant, emission at 458 nm.

no matter how long the solution stood and whatever the nanoparticle formed (Figure 3C). It indicated that electron transfer does occur from the 9-CHF core to Cu2+. Both the 9-CHF core and two rotatable aryls at the 2, 7-positions of 9-CHF worked essentially for emission at the lower energy band.

5. Monitoring Aggregate Formation. By using dynamic light scattering (DLS), we tracked the aggregate formation process of 1 and CuCl2 in THF solution (Figure 4C). Combining the changes of absorption at 392 nm (Figure 4A) and emissions at 377, 458 nm (Figure 4B), a turning point at about 4 min was



Figure 3. (A) UV-vis spectra and (B) fluorescence spectra (ex 347 nm) of 4 in THF with 0.5 equiv CuCl2. (C) TEM image and fluorescent image (under 365 nm) after keeping the solution of 4 and 0.5 equiv CuCl2 at room temperature for 2 h.

Figure 4. Trend of absorption at 392 nm (A), emissions at 377, 458 nm (B), and aggregate growth (C) in THF solution of 1 after adding 0.5 equiv CuCl2; TEM photography at 4 min (D), 10 min (E), and 2 h (F), respectively.

SCHEME 2: Working Mechanism of Aggregate Formation

clearly observed. These results were in good accordance with the TEM photography (Figure 4D-F). From the beginning to 4 min, addition of CuCl2 to the THF solution of 1 resulted in the aggregate formation and the size growth to 100 nm. Afterward, a mutation occurred. As the size of aggregates increased dramatically, absorption started to decrease and emissions started to increase. Intermolecular interactions between 1 and Cu2+ triggered the electron transfer from the 9-CHF core to metal cation, which simultaneously resulted in the formation of aggregates that was accelerated by the cooperation of chloride anion via electrostatic interactions. As a result, the solution was bleached and the fluorescence was turned on (Scheme 2). Moreover, both LE emission enhancement and aggregation-induced emission (AIE) at lower energy band

obeyed first-order kinetics, which further referred that the rate constant was associated only with the concentration of aggregates which dispersed in solution. 6. More Examples Showing AIE at Lower Energy Band. Many fluorescent compounds that are nonemissive in dilute solutions could be induced to emit intensive light in aggregates. However, most of the AIE/AIEE examples reported by Tang,7 Swager,5 Park,6 ours,9 and other groups8 focused on the emission enhancemnt of the LE band. Combination of 1 and cupric chloride might be the first example causing both LE emission enhancement and AIE at lower energy band due to cooperation of the aggregate formation and the electron transfer. In order to test more examples with this phenomenon, a number of

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TABLE 1: Photophysical Data of Compounds with CuCl2 in THF Solutions absorption

LE emission 3

λabs/ (nm/10 ) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

324/24.0, 392/11.8 322/31.6 246/69.4, 379/35.4 318/57.8, 406/16.5 324/28.3, 388/17.3 332/33.4, 386/18.9 308/15.6, 383/21.8 350/44.0, 402/15.9 340/64.5, 390/23.6 348/66.9, 396/19.9 361/88.6 355/71.9 298/39.3, 354/61.8 370/73.9 371/100

λ ex/λ

em

(nm)

324/377 325/377 347/379, 399 326/379 326/357, 374 314/334 338/375, 393 344/384, 403 360/402, 423 374/440 369/408, 428 365/411 336/367, 385 385/416, 439

Φ0

a

lower energy band emission b

-1

KLE (min )

0.004 0.21 0.02 0.05 0.01 0.006 0.002 0.006 0.011 0.008 0.006 0.002 0.005 0.002

0.21 0.15 0.26 0.16 0.12 0.19 0.23 0.22 0.33 0.23 0.18 0.57

ΦLE

a,d

λex/λem (nm)

KAIEb (min-1)

ΦAIEc,d

0.19 0.21 0.26 0.18 0.17 0.08 0.22 0.55 0.51 0.22 0.031 0.007 0.20 0.07

372/458 376/470 384/471 352/422 409/455, 482 394/476, 496 412/491 419/500 417/493 416/495, 517 389/479 433/486, 521

0.17 0.17 0.18 0.17 0.36 0.23 0.30 0.30 0.22 0.24 0.22 0.43

0.19 0.26 0.15 0.09 0.39 0.48 0.43 0.37 0.24 0.13 0.31 0.34

Quantum yields were calculated based on trans, trans-1,4-diphenylbuta-1,3-diene as the standard (Φ ) 0.44). b Rate constants were evaluated from ref 14. c Quantum yields were calculated based on 9, 10-diphenylanthracene as standard (Φ ) 0.95). d ΦLE and ΦAIE were calculated 1 h after 0.5 equiv CuCl2 was added into the THF solutions of 9-CHF derivatives at room temperature. a

SCHEME 3: AIE Efficiency at Lower Energy Band Tuned by Rotation Groups

compounds with 9-CHF core were synthesized. Photophysical data of these compounds were summarized in Table 1. Besides compound 1, compounds 5-9 also possessed LE emission enhancement and AIE at lower energy band (Scheme 3). Kinetic trackings of the cooperation of compounds 5-9 and cupric chloride via absorption, emission, and TEM are presented in Figure S5-S9, respectively. Due to four methyl groups attached on phenyl rings (7), free rotations of σ-bonds were partially depressed via steric hindrance. Variable of dihedral angle of 7, from single molecule to aggregates, was less than that of 6. Therefore, emission efficiencies at two bands of 7 in its aggregates were less expressed in comparison with those of 6, respectively (Table 1, compounds 6 and 7). By extension of the conjugation of 6-8, red-shifted absorption and red-shifted emission were expectantly observed. Two more rotatable σ-bonds existed in 8 than that in 6 as the interposition of triple bond. Emission efficiencies at two bands were thereafter increased because the nonradiative decay of 8 was more efficiently saved in comparison with that of 6 in their aggregates (Table 1, compounds 6 and 8). With two more phenyls on 6, 9 had more opportunities to restrict free rotation of σ-bonds. As a result, emission efficiencies at two bands of 9 in its aggregates were determined to be 0.55 and 0.48 for LE band and lower energy band, respectively (Table 1, compounds 6 and 9). Therefore, it could be preliminarily concluded that the restricted

free rotation of σ-bonds in their aggregate states was the key factor for AIEE at LE band and AIE at lower energy band. For comparison, compounds 10-15 were designed and synthesized, which possessed different terminal groups (Scheme 4). Kinetic trackings of the cooperation of compounds (10-15) and cupric chloride via absorption, emission, and TEM are presented in Figures S10-S15, respectively. All of these compounds exhibited AIEE at LE band and AIE at lower energy band. The maximum emission efficiency for AIE at lower energy band was determined to be 0.43 for 10 among these compounds. For compounds 11 and 15, it was not surprising that one of the phenyl groups in 11 did not contribute to AIE due to the fact that it was perpendicular to its backbone. A similar situation was observed for 15. For compounds 12-14, all terminal phenyls were blocked, and the free rotation of terminal phenyl groups was efficiently inhibited. 7. Emission vs Concentration. For the concentration quenching occurring mostly in organofluorescent compounds, emissions associated with concentrations were recorded after solutions stood for 24 h for to complete electron transfer (Figure 5). Keeping the ratio of 1 to CuCl2 at 2:1, two emission bands were demonstrated as the concentration of 1 varied from 1 × 10-6 to 5 × 10-4 mol L-1. The turning point could be clearly seen as the concentration of 1 reached 5 × 10-5 mol L-1. Beyond this point, AIE at lower energy band kept going while emission



SCHEME 4: AIE Efficiency at Lower Energy Band Tuned by Terminal Groups

at LE band decreased dramatically. It implied that AIE occurred at lower energy band, while aggregation-causing quenching (ACQ) happened at LE band at higher concentration. A similar situation was observed in the case of 11, the turning point of which was observed to be 1 × 10-5 mol L-1. 8. Emission Enhancement at Low Temperature. Restricted intramolecular rotation was assigned as the main reason leading to AIE as previously studied. In order to limit the free rotation of two phenyl rings of 6, emission spectra of 6 were recorded at freezing temperature. As the temperature changed from 28 to -107 °C, emission enhancement was detected, and it was magnified to twofold of its initial value, but their emission efficiencies were relatively low (Figure 6A). After addition of CuCl2 for 2 h and cooling, the emission efficiency was magnified twofold at LE band (Figure 6B) and fourfold at lower energy band (Figure 6C) as the temperature decreased from 28 to -107 °C. 9. Anion Effect on AIE at Lower Energy Band. It is notable that AIE at lower energy band depended on different anions. When CuCl2, CuBr2, Cu(Ac)2, Cu(NO3)2, CuSO4, and

Cu(OTf)2 were used as Cu2+ source, respectively, only the cases with Cl- or Br- presented the AIE at lower energy band after 2 h. Cl- showed the maximum variable. Two hours after addition of various copper salts to the solutions of 1, aggregates gradually grew, and the size of aggregates was determined to be 149, 142, 178, and 171 nm for Cu(OTf)2, Cu(NO3)2, Cu(Ac)2, and CuSO4, respectively. Addition of CuCl2 or CuBr2 to the solution of 1 afforded the aggregates also, but with the size larger than 500 nm (Figure 7A). If the solution of 1 and CuSO4 stood for 48 h, the size of aggregates grew to 400 nm and the turn-on fluorescence at lower energy band could also be observed. Therefore, it is becoming clear that anions worked for the turn-on fluorescence at lower energy band, but with different rates. A similar phenomenon was observed for 6. After the solution of 6 and various salts stood for 2 h, photos were taken when solutions were exposed to UV light (Figure 7B). Only the solution with both Cu2+ and Cl- caused the turn-on fluorescence. An AND logic gate was thereby established (Figure 7C).

Figure 5. Emissions associated with various concentrations of 1 (A) or 11 (B) with 0.5 equiv CuCl2, after 24 h.

Figure 6. Emissions of 6 at different temperatures: (A) emissions of 6 with 0.5 equiv CuCl2 in THF at different temperatures, ex 326 nm (B) and ex 384 nm (C).

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Figure 7. (A) DLS characterization of nanoparticles of 1 in THF with 0.5 equiv various copper salts. (B) Fluorescence images of 6 (under 365 nm): (1) pure solution, (2) with 0.5 equiv CuSO4, (3) with 1 equiv NaCl, (4) with both 0.5 equiv CuSO4 and 1 equiv NaCl in THF solution. (C) AND logic gate.

Figure 8. (A) X-ray diffraction structure of 1. (B) Packing arrangement in crystal structure of 1, with C-H...π hydrogen bonds marked by dashed lines, d1 ) 3.01 Å, ∠C-H...π ) 141.34°.

Figure 9. Packing arrangement in crystal structure of 11, with C-H...π hydrogen bonds marked by dashed lines, d1 ) 2.92 Å, ∠C-H...π ) 137.66°; d2 ) 3.32 Å, ∠C-H...π ) 140.89°; and d3 ) 3.19 Å, ∠C-H...π )149.50°.

10. Stacking Model in Aggregates. In order to understand the stacking model in the aggregates, we checked geometric structures and packing arrangements of 1 and 11 in their crystalline states. 1 has a symmetrical plane (Figure 8A). The seven-membered ring is slightly turned-up relative to the fluorene plane with a dipole moment to satisfy several aromaticities. Two phenylenes are slightly twisted to the central fluorene (∠C11-C12-C13-C14 ) -45.17°), while two terminal phenyls are almost perpendicular to their carrier (∠C1-C6-C7-C12 ) -53.48°). There are 18 molecules in a unit cell. Two driving forces for the molecular stacking are antiparallel π-π interactions between adjacent 9-CHFs and C-H...π van der Waals interactions as indicated (Figure 8B), respectively. As the conjugation extended, compound 11 possesses neither antiparallel nor parallel π-π interactions between adjacent 9-CHFs. The only intermolecular interaction for molecular stacking is the C-H...π van der Waals interactions as indicated (Figure 9). In THF solution, a sandwich complex formed between Cu2+ and 9-CHFs. The ratio of Cu2+ and 9-CHFs was found to be 1:2 based on the Job’s plot. Cu2+ was in between two 9-CHFs,

similar to the structure of ferrocene. Thus, the internal Cu2+ directly inhibited the π-π stacking of two 9-CHFs. Moreover, due to the electron transfer process, the organic part held the positive charge which also diminished the possible π-π stacking between two 9-CHFs of two adjacent sandwiches because of the electrostatic repulsion. As a result, any π-π stacking between 9-CHFs was thereby inhibited. The possible C-H...π van der Waals interactions and the function of specific anions, such as Cl-, Br-, induced the single complex to form aggregates and expressed the AIE at lower energy band. Conclusion In this contribution, emission enhancement at LE band and aggregation induced emission at lower energy band were simultaneously observed for 2,7-diaryl-9-cyclohepatrienylfluorenes and cupric chloride in THF solution using two excitation wavelengths. By kinetically tracking the nanoparticle formation and comparatively studying the structural effect, a working mechanism was proposed. Electron transfer cooperating with the aggregate formation turned on the fluorescence. The reason

Electron Transfer and AIEE of 9-CHFs was ascribed to the restricted intramolecular rotation in their aggregates, and the model might be used for better understanding the mechanism of AIE and could be designed as an AND logic gate for further application. Experimental Section 1. General Method. Tetrahydrofuran for UV-vis and emission spectroscopic measurements was redistilled. Commercially available reagents were used without further purification unless ¨ CHI otherwise stated. Melting points were recorded on a BU 535. 1H and 13C NMR spectra were obtained on a Bruker AVANCE DMX500 or Bruker AVANCE DMX400 spectrometer in CDCl3 or DMSO-d6 as solvents with tetramethylsilane (TMS) as internal standard. UV-vis absorption spectra were recorded on a Shimadzu UV-2450 spectrophotometer. Steadystate fluorescence spectra were recorded on a Shimadzu RF5301PC spectrofluorophotometer. The time-resolved fluorescence data were obtained with an EDINBURGH FLS 920 timeresolved spectrofluorimeter. All electron impact mass spectra were recorded on an Agilent 5973N MSD instrument, and all high-resolution mass spectra (HRMS) were recorded on a Waters Micromass GCT instrument or Ionspec 4.7 T FTMS mass spectrometer. TEM micrographs were obtained on a JEM1200EX transmission electron microscope. All reactions were carried under N2. Dynamic light scattering (DLS) measurements of the colloidal particles were conducted on a Brookhaven 90 Plus Particle Size Analyzer, at a detection angle of 90° at 23 °C. X-ray measurements were carried out on a CCD area detector diffractometer by using graphite-monochromated Mo KR radiation (λ ) 0.710 73 Å). Intensity data were collected in the ω-scan mode. The structures of 1 and 11 were solved by direct methods (SIR97 program). The hydrogen atoms were placed in calculated positions at a bond distance of 0.93 Å to aryl C and 0.97 Å to alkyl C. 2. Synthesis. 2,7-Dibromo-9-(cycloheptatrienylidene)fluorene, 2,7-dibromo-9-(2,4,6-cycloheptatrienyl)fluorene, 3, 5, 6, and 8 were prepared and characterized as described previously.16,17 2,7-Di(biphenyl-2-yl)-9-(cycloheptatrienylidene)fluorene (1). A mixture of 2,7-dibromo-9-(cycloheptatrienylidene)fluorene (150 mg, 0.36 mmol), biphenyl-2-ylboronic acid (216 mg, 1.09 mmol), K2CO3 (0.73 g, 5.3 mmol), and Pd(PPh3)4 (10 mg, 0.013 mmol) in 25 mL of toluene/ethanol/degassed water (2:2:1) was refluxed for 24 h. After cooling, methylene chloride (30 mL) was added. The organic layer was washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After filtration, the filtrate was evaporated under reduced pressure. The crude product was purified by column chromatography (silica gel) using n-hexane/dichloromethane as eluent. In this way, 1 (150 mg, 74% yield) was obtained as an orange solid. 1H NMR (500 MHz, CDCl3): δ 7.67 (d, J ) 7.8 Hz, 2H), 7.54-7.52 (m, 2H), 7.51-7.45 (m, 8H), 7.33-7.29 (m, 10H), 7.24-7.22 (m, 2H), 6.40-6.39 (m, 2H), 6.16-6.12 (m, 2H), 5.82 (d, J ) 11.0 Hz, 2H). 13C NMR (125 MHz, CDCl3): δ 142.27, 141.11, 140.84, 139.64, 138.54, 137.91, 136.25, 132.69, 131.07, 130.97, 130.27, 130.02, 129.40, 129.22, 128.39, 128.23, 127.89, 127.66, 127.47, 126.86, 119.68. HRMS: calcd. for C44H30[M+], 558.2352; found, 558.2342. Compound 2. Compound 2 was prepared from 2,7-dibromo9-(2,4,6-cycloheptatrienyl)fluorene by a similar method as 1. Yield 74%. mp 179.7-180.2 °C. 1H NMR (400 MHz, CDCl3): δ 7.61 (d, J ) 7.7 Hz, 2H), 7.46-7.39 (m, 8H), 7.24-7.22 (m, 4H), 7.18-7.09 (m, 10H), 6.55-6.53 (m, 2H), 6.06-6.02 (m, 2H), 4.77 (dd, J ) 9.3, 6.5 Hz, 2H), 3.85 (d, J ) 6.1 Hz, 1H),

J. Phys. Chem. C, Vol. 114, No. 43, 2010 18709 2.23-2.18 (m, 1H). 13C NMR (100 MHz, CDCl3): δ 146.10, 141.62, 140.86, 140.62, 140.04, 139.64, 130.73, 130.70, 129.85, 128.92, 127.96, 127.50, 127.47, 127.41, 126.57, 125.57, 125.02, 119.26, 46.59, 42.33. MS(EI): m/z 560.2 (M+). HRMS: calcd. for C44H32[M+], 560.2504; found, 560.2501. Compound 4. To a flame-dried flask with a magnetic stirrer was added a solution of 1 (20 mg, 0.036 mmol) in dry dichloromethane (35 mL). The solution was degassed by bubbling nitrogen for 30 min, and then FeCl3 (0.46 g, 2.8 mmol) powder was added. A constant nitrogen stream was carried out during the entire reaction, and the reaction was quenched with methanol (20 mL) after 0.5 h. The solution was diluted by THF/ CH2Cl2 and washed with water. The organic layer was evaporated under reduced pressure. The crude product was purified by column chromatography (silica gel) using n-hexane/dichloromethane as eluent first and then using dry THF. In this way, 4 (16 mg, 80% yield) was obtained as an orange solid. 1H NMR (500 MHz, CDCl3): δ 9.20 (s, 2H), 9.10 (s, 2H), 8.86 (d, J ) 8.0 Hz, 2H), 8.66-8.63 (m, 6H), 7.75-7.64 (m, 8H), 7.20 (d, J ) 10.8 Hz, 2H), 6.74-6.69 (m, 4H). HRMS: calcd. for C44H26[M+], 554.2030; found, 554.2029. 2,7-Bis(2,6-dimethylphenyl)-9-(cycloheptatrienylidene)fluorene (7). 7 was prepared by a similar method as 1. Yield 60%. 1 H NMR (500 MHz, CDCl3): δ 7.86 (d, J ) 7.6 Hz, 2H), 7.76 (s, 2H), 7.25-7.22 (m, 2H), 7.19- 7.17 (m, 4H), 7.14 (dd, J ) 7.6, 1.0 Hz, 2H), 6.91 (d, J ) 11.1 Hz, 2H), 6.50-6.48 (m, 2H), 6.44-6.40 (m, 2H), 2.14 (s, 12H). 13C NMR (125 MHz, CDCl3): δ 142.70, 139.60, 139.23, 138.39, 136.96, 136.71, 132.98, 130.21, 129.78, 128.06, 127.60, 127.30, 125.52, 119.88, 21.26. MS(EI): m/z 462 (M+). HRMS: calcd. for C36H30[M+], 462.2348; found, 462.2352. 2,7-Di(biphenyl-4-yl)-9-(cycloheptatrienylidene)fluorene (9). 9 was prepared by a similar method as 1. Yield 74%. 1H NMR (500 MHz, CDCl3): δ 8.24 (s, 2H), 7.85 (d, J ) 7.8 Hz, 2H), 7.77-7.72 (m, 8H), 7.68 (d, J ) 7.2 Hz, 4H), 7.62 (dd, J ) 7.8, 1.3 Hz, 2H), 7.49 (dd, J ) 7.7 Hz, 4H), 7.38 (dd, J ) 7.4 Hz, 2H), 7.07 (d, J ) 10.5 Hz, 2H), 6.65-6.53 (m, 4H). 13C NMR (125 MHz, CDCl3): δ 141.16, 141.02, 140.31, 139.88, 139.58, 138.90, 136.97, 133.11, 130.03, 129.75, 129.10, 127.91, 127.83, 127.61, 127.32, 126.40, 123.85, 120.30. MS(EI): m/z 558 (M+). HRMS: calcd. for C44H30[M+], 558.2348; found, 558.2353. 2,7-Bis(4-(2-phenylprop-1-enyl)phenyl)-9-(cycloheptatrienylidene)fluorene (10). 10 was prepared by a similar method as 1. Yield 90%. 1H NMR (500 MHz, CDCl3): δ 8.23 (s, 2H), 7.84 (d, J ) 7.8 Hz, 2H), 7.70 (d, J ) 8.1 Hz, 4H), 7.61 (d, J ) 7.7 Hz, 2H), 7.57 (d, J ) 7.6 Hz, 4H), 7.50 (d, J ) 8.1 Hz, 4H), 7.40 (dd, J ) 7.6 Hz, 4H), 7.32 (dd, J ) 7.3 Hz, 2H), 7.07 (d, J ) 10.7 Hz, 1H), 6.91 (s, 2H), 6.58-6.56 (m, 2H), 2.38 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 144.29, 140.21, 139.87, 139.67, 138.85, 137.92, 137.57, 136.88, 133.10, 130.04, 129.94, 129.71, 128.63, 127.61, 127.49, 127.26, 126.34, 126.29, 123.79, 120.27, 17.95. MS(EI): m/z 638.3 (M+). HRMS: calcd. for C50H38[M+], 638.2974; found, 638.2972. 2,7-Bis(4-(2,2-diphenylWinyl)phenyl)-9-(cycloheptatrienylidene)fluorine (11). 11 was prepared by a similar method as 1. Yield 90%. 1H NMR (400 MHz, CDCl3): δ 8.12 (s, 2H), 7.76 (d, J ) 7.9 Hz, 2H), 7.51 (d, J ) 7.9 Hz, 2H), 7.46 (d, J ) 7.9 Hz, 4H), 7.42-7.27 (m, 20H), 7.15 (d, J ) 8.0 Hz, 4H), 7.04 (s, 2H), 7.00 (d, J ) 10.8 Hz, 2H), 6.55-6.50 (m, 4H). 13C NMR (125 MHz, CDCl3): δ 143.69, 142.87, 140.74, 140.29, 139.75, 139.36, 138.77, 136.78, 136.55, 133.03, 130.64, 130.27, 130.00, 129.64, 129.04, 128.48, 127.97, 127.84, 127.76, 126.95,

18710


126.16, 123.52, 120.15. MS(EI): m/z 762.3 (M+). HRMS: calcd. for C60H42[M+], 762.3287; found, 762.3276. Compound (12). 12 was prepared by a similar method as 1. Yield 56%. 1H NMR (400 MHz, CDCl3): δ 8.11 (s, 2H), 7.75 (d, J ) 7.9 Hz, 2H), 7.54-7.45 (m, 8H), 7.33 (d, J ) 7.5 Hz, 2H), 7.23-7.19 (m, 6H), 7.15-7.08 (m, 10H), 6.99 (d, J ) 10.8 Hz, 2H), 6.85 (s, 2H), 6.55-6.49 (m, 4H), 3.56 (s, 2H), 3.42 (s, 2H), 3.08 (s, 2H), 2.92 (s, 2H). 13C NMR (125 MHz, CDCl3): δ 144.09, 142.12, 140.84, 140.25, 139.74, 139.40, 139.32, 138.76, 137.84, 136.35, 133.03, 130.49, 130.00, 129.94, 129.71, 129.64, 128.65, 128.54, 128.22, 128.08, 127.64, 126.97, 126.82, 126.42, 126.18, 123.54, 120.15, 33.86, 32.34. MS(EI): m/z 814.4 (M+). HRMS: calcd. for C64H46[M+], 814.3600; found, 814.3609. 2,7-Bis(dibenzosuberenylidenemethyl)-9-(cycloheptatrienylidene)fluorine (13). 13 was prepared by a similar method as 1. Yield 51%. 1H NMR (400 MHz, CDCl3): δ 8.10 (s, 2H), 7.75 (d, J ) 7.9 Hz, 2H), 7.57 (d, J ) 7.6 Hz, 2H), 7.49 (d, J ) 7.9 Hz, 2H), 7.48-7.41 (m, 8H), 7.35-7.31 (m, 6H), 7.24 (d, J ) 3.8 Hz, 4H), 7.05-6.94 (m, 10H), 6.56-6.49 (m, 6H). 13 C NMR (125 MHz, CDCl3) δ 142.87, 142.64, 140.31, 139.75, 139.42, 138.76, 137.79, 136.77, 136.09, 135.17, 134.60, 133.04, 132.13, 131.73, 131.46, 130.00, 129.93, 129.64, 129.41, 129.18, 129.15, 128.62, 127.62, 127.28, 127.20, 126.88, 126.17, 123.53, 120.15. MS(EI): m/z 810.3 (M+). HRMS: calcd. for C64H42[M+],810.3287; found, 810.3291. 2,7-Bis(4-((9H-fluoren-9-ylidene)methyl)phenyl)-9-(cycloheptatrienylidene)fluorine (14). 14 was prepared by a similar method as 1. Yield 49%. 1H NMR (500 MHz, CDCl3): δ 8.30 (s, 2H), 7.90 (d, J ) 7.8 Hz, 2H), 7.83 (d, J ) 7.4 Hz, 2H), 7.80 (dd, J ) 8.2, 1.8 Hz, 6H), 7.75-7.74 (m, 10H), 7.69 (dd, J ) 7.8, 1.4 Hz, 2H), 7.40-7.33 (m, 6H), 7.14-7.11 (m, 4H), 6.62-6.61 (m, 4H). 13C NMR (125 MHz, CDCl3): δ 141.77, 141.59, 139.99, 139.86, 139.46, 139.06, 136.82, 136.03, 133.18, 130.27, 130.02, 129.91, 128.88, 128.50, 127.50, 127.28, 127.22, 126.98, 126.42, 124.75, 123.75, 120.53, 120.44, 120.05, 119.88. MS(EI): m/z 758.3 (M+). HRMS: calcd. for C60H38[M+], 758.2974; found, 758.2978. 2,7-Bis((4-(2,2-diphenylWinyl)phenyl)ethynyl)-9-(cycloheptatrienylidene)fluorine (15). A mixture of 1-(2,2-diphenylvinyl)4-iodobenzene (0.42 g, 1.09 mmol), 19 (100 mg, 0.36 mmol), CuI (20 mg, 0.1 mmol), PPh3 (26.2 mg, 0.1 mmol), and Pd(PPh3)2Cl2 (10 mg, 0.013 mmol) in Et3N (40 mL) was refluxed for 12 h. After cooling to room temperature, the solvent was removed by evaporation. The residue was purified by column chromatography. In this way, 21 was obtained in 95% yield (280 mg) as a yellow solid. 1H NMR (500 MHz, CDCl3): δ 8.07 (s, 2H), 7.69 (d, J ) 7.8 Hz, 2H), 7.46 (d, J ) 7.9 Hz, 2H), 7.35-7.30 (m, 20H), 7.22-7.21 (m, 4H), 7.03-6.97 (m, 8H), 6.61-6.59 (m, 4H). 13C NMR (125 MHz, CDCl3): δ 143.80, 143.42, 140.37, 139.02, 138.19, 137.69, 133.24, 131.43, 130.62, 130.55, 130.26, 129.94, 129.76, 128.98, 128.50, 127.98, 127.91, 127.76, 121.69, 121.65, 120.09, 91.49, 89.99. HRMS: calcd. for C64H42[M+], 810.3287; found, 810.3283. Acknowledgment. We thank the National Nature Science Foundation of China (20972137, J0830413) and the FundamentalResearchFundsfortheCentralUniversities(2009QNA3011) for financial support. Supporting Information Available: Copies of 1H NMR, C NMR, HRMS, and photophysical spectra for products; crystallographic information files for compounds 1 and 11. This material is available free of charge via the Internet at http:// pubs.acs.org.

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JP1068126

Electron Transfer and Aggregate Formation Coinduced Emission

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