Benzo[4,5]cyclohepta[1,2-b]fluorene: an isomeric motif for pentacene containing linearly fused five-, six- and seven-membered rings† †Electronic supplementary information (ESI) available: Synthetic procedures and characterization data for all new compounds; general experimental method; additional sp

A new class of conjugated polycyclic molecules containing a C6–C5–C6–C7–C6 polycylic framework was synthesized. Both experiments and calculations show different electron structures in comparison to their pentacene isomers.


5,11-Dimesityl-5,11-dihydrobenzo[4,5]cyclohepta[1,2-b]fluorene-5,11-diol (12c)
To a solution of 2-Bromomesitylene (241 mg, 1.21 mmol) in 10 ml of anhydrous THF at −78 °C was added 0.78 mL of 1.6 M n-butyllithium in hexane (1.24 mmol) dropwise under a nitrogen atmosphere, and the resulting mixture was stirred for 0.5 hour at −78 °C. To the mixture was added 61.6 mg (0.200 mmol) of benzo [4,5]cyclohepta[1,2-b]fluorene-5,11-dione (11) under a nitrogen atmosphere, and the resulting mixture was warmed to room temperature. After being stirred for 5 hours at room temperature, the reaction mixture was quenched with water and then extracted with diethyl ether for three times. The organic layers were combined, washed with saturated brine, dried with anhydrous Na 2 SO 4 , and concentrated under a reduced pressure. The resulting gel-like solid was purified by column chromatography on silica gel using hexane/diethyl ether (v/v changed from 10/1 to 3/1) as eluent for gradient elution yielding the diol 12c as two separated diastereomers.

5,11-Bis((triethylsilyl)ethynylbenzo[4,5]cyclohepta[1,2-b]fluorine (5b)
0.12 mL of acidic SnCl 2 saturated solution (SnCl 2 saturated in 37% HCl) was added to a solution of 67.3 mg (0.100 mmol) of diol 12b (a mixture of two diastereomers) in 50 mL of THF at 0 o C. The immediately formed dark green solution was stirred at room temperature in dark for 30 minutes, and then diluted with 50 mL of water and extracted with diethyl ether. The organic layer was separated, washed with water, NaHCO 3 aq. solution and saturated brine successively, dried with anhydrous Na 2 SO 4 , and then concentrated under a reduced pressure. The crude product was purified by column chromatography on deactivated silica gel containing 5% water with CH 2 Cl 2 /hexane (1/100, v/v) as eluent in dark yielding 41.5 mg (65%) of 5,11-bis((triethylsilyl)ethynylbenzo [4,5] Preparation of deactivated silica gel: 1.0 g of water was added to 20 g of silica gel suspended in hexane. The suspension was stirred until block solids disappeared. Then the suspension was used to fill a column for chromatography.

5,11-Dimesitylbenzo[4,5]cyclohepta[1,2-b]fluorene (5c)
0.30 mL of acidic SnCl 2 saturated solution (SnCl 2 saturated in 37% HCl) was added to a solution of 54.9 mg (0.100 mmol) of diol 12c (a mixture of two diastereomers) in 50 mL of THF at 0 °C. The mixture was stirred at room temperature in dark for 10 hours. Then the resulting dark-green mixture was diluted with 50 mL of water and extracted with diethyl ether. The organic layer was separated, washed with water, NaHCO 3 aqueous solution and saturated brine successively, dried with anhydrous Na 2 SO 4 , and then concentrated under a reduced pressure. The crude product was purified by column chromatography on deactivated silica gel containing 5% water with CH 2 Cl 2 /hexane (1/40, v/v) as eluent in dark yielding 36.0 mg (70%) of 5,11-dimesitylbenzo [4,5] Scheme S1 Alternative synthesis of diketone 10.
The diacid as obtained above was dissolved in 30 mL of anhydrous ethanol. To the solution 5 mL of concentrated H 2 SO 4 (5 mL) was slowly added, and the reaction mixture was refluxed overnight. After cooled to room temperature, the mixture was poured into water and extracted with ethyl acetate. The organic layer was washed by water, dried over anhydrous Na 2 SO 4 , and concentrated under a reduced pressure. The residue was purified by column chromatography on silica using hexane/ethyl acetate (15/1, v/v) as eluent yielding 3.

DFT calculation details
Density functional theory calculations were employed with Gaussian 09 package, 1 utilizing the (U)CAM-B3LYP 2-4 level of theory with Pople basis set 6-31G* 5-7 for all molecules in the gas phase. NICS values at the (U)CAM-B3LYP/6-31G* level using the standard GIAO procedure (NMR pop=NCSall). 8 UV-vis-NIR absorption spectra of 5b and 5c in the closed-shell form were generated assuming an average UV-vis width of 4000 cm -1 at half-height using the SWizard program. 9      H-0->L+0(7%) S15

Fabrication and characterization of organic thin film transistors
(1) Dip coating thin films of 5b and fabrication of OTFTs The substrate used in the fabrication is a highly n-doped silicon wafer with a 300 nm-thick SiO 2 layer on the top. To form dip-coated films, a 1 cm × 0.5 cm silicon wafer was immersed vertically in a 2.5 mg/ml solution of 5b in n-hexane and then was pulled up with a constant speed of 5.3 μm/s as controlled with a Longer Pump TJ-3A syringe pump controller.
To fabricate OTFTs, the solution-processed films were placed in a vacuum oven overnight to remove solvent residues. Then top contact drain and source gold electrodes were vacuum-deposited afterwards through a shadow mask onto the films by an Edward Auto 306 vacuum coating system with a Turbomolecular pump at a pressure of 4.0 × 10 −6 torr or lower, with a deposition rate of ca. 2 nm/minute to a thickness about 30 nm as measured by a quartz crystal sensor, and the resulting semiconducting channels were 50 μm (L) × 1 mm (W), 100μm (L) × 1mm (W), 150 μm (L) × 1mm (W), 50 μm (L) × 2mm (W) and 100 μm (L) × 2mm (W).
(2) Characterization of the films and OTFTs.
Polarized optical images of the dip coated films were obtained using Nikon 50IPOL microscope. XRD measurement with θ-2θ scan mode was carried out on a SmartLab X-Ray Refractometer. The current-voltage measurement of thin-film transistors was conducted using a 4PROBES TECH ST-102C probe station and a Keithley 4200 Semiconductor Characterization System in air under ambient conditions.