Access tetracoordinate boron-doped polycyclic aromatic hydrocarbons with aggregation-induced emission under mild conditions

(s, 3H, -CH 3 1.32 (s, 9H, t Bu), 1.00 (s, 3H, -CH 3 13 C NMR (126 MHz, CDCl 3 ) δ 153.81(Py), 151.08(Py), 143.70, 143.45, 143.17, 142.97, 142.18, 141.99, 141.85, 141.79, 141.56, 139.34, 137.93, 135.40(Py), 130.12, 129.79, 126.63, 125.54, 125.24, 124.51, 124.20, 124.02, 120.94, 120.14, 119.55(Py), 118.12, 117.87, 116.79, 116.36, 115.92, 113.95, 113.48, 112.96, 35.22 t 35.14 t Bu), 34.86 t Bu), 34.66 t Bu), 32.37 t Bu), 32.31 t Bu), 32.17 ( t Bu), 32.04 ( t Bu), 22.50 3 21.99 3 20.74 (-CH 3 HRMS(ESI) (m/z): [M+H] + calcd for C 54 H 61 BN 3 762.4959; found: 762.4951.


Experimental section 1.1 General information
All reactions were carried out under an atmosphere of dry nitrogen.
Dichloromethane was freshly distilled over calcium hydrogen and stored under nitrogen prior to use. All starting materials were purchased from Energy Chemical and Leyan and used without further purification. Proton nuclear magnetic resonance ( 1 H NMR) and carbon nuclear magnetic resonance ( 13 C NMR) spectra were recorded on Bruker Avance 400 or 500 MHz spectrometers. All Photophysical property measurements were under nitrogen atmosphere. UV/vis and fluorescence measurements were performed on a Jasco V-770 UV/vis spectrophotometer and a F97 Pro fluorescence spectrophotometer, respectively. Quantum efficiencies were determined using an absolute PL quantum yield spectrometer C11347. Phosphorescence and photoluminescence decay curves were recorded on an Edinburgh Instruments FLS980 spectrophotometer equipped with 365 nm picosecond pulsed LEDs and decay curves were analyzed using the Edinburgh Instruments F980 software. Bpin-carbazole 1 and 7-Bpin-indole 2 were synthesized according to the reported procedure.

Synthesis of Compound NBNN-1
A mixture of 2-Methoxyethanol (48 ml) and water (8 ml) was stirred and degassed by nitrogen for 1 hour. 2,6-dibromopyridine (830 mg, 3.53 mmol), Bpin-carbazole (3.12 g, 7.70 mmol), Pd(PPh3)4 (200 mg, 0.173 mmol) and K2CO3 (1.45 g,10.51 mmol) were add to the mixed solvents. The reaction mixture was heated to 80 ℃ and stirred for 16 hours. The reaction mixture was quenched with water and then the mixture was washed with brine and CH2Cl2 for three times. The combined organic layers were dried over magnesium sulfate and then the solvents were evaporated under reduced pressure.

Method 1
Boron tribromide (0.1 mL) was added to a solution of 1a (100 mg, 0.157 mmol) in CH2Cl2 (2 mL) under nitrogen atmosphere. The reaction mixture was stirred at room temperature for 2 hours. Phenylmagnesium bromide (1 M in tetrahydrofuran, 4 ml, 4.0 mmol) was dripped into the reaction mixture and the reaction mixture was stirred for 1.5 hours. The reaction mixture was quenched with water and then the mixture was washed with brine and CH2Cl2 for three times. The combined organic layers were dried over magnesium sulfate and then the solvents were evaporated under reduced pressure.
Purification of the crude product by alumina column chromatography (petroleum ether/ethyl acetate = 30:1) afforded the product NBNN-1 as an orange solid in 78% yield (88 mg, 0.122 mmol). The product was confirmed by X-ray diffraction analysis.

Synthesis of Compound NBNN-4
Boron tribromide (0.1 mL) was added to a solution of 1a (100 mg, 0.157 mmol) in CH2Cl2 (2 mL) under nitrogen atmosphere. The reaction mixture was stirred at room temperature for 2 hours. The reaction mixture was quenched with N,N-diisopropylethylamine (0.34 ml, 1.96 mmol) and then the mixture was washed with brine and CH2Cl2 for three times. The combined organic layers were dried over magnesium sulfate and then the solvents were evaporated under reduced pressure.

Synthesis of Compound NBNN-5
A mixture of 1,2-dimethoxyethane (DME, 24 ml) and water (4 ml) was stirred and degassed by nitrogen for 1 hour. 2,6-dibromopyridine (592 mg, 2.52 mmol), 7-Bpinindole (1.34 g, 5.51 mmol), Pd(PPh3)4 (144 mg, 0.124 mmol) and K2CO3 (1.03 g, 7.45 mmol) were add to the mixed solvents. The reaction mixture was heated to 80 ℃ and stirring for 16 hours. The reaction mixture was quenched with water and then the mixture was washed with brine and CH2Cl2 for three times. The combined organic layers were dried over magnesium sulfate and then the solvents were evaporated under reduced pressure. Purification of the crude product by silica gel column Boron tribromide (0.1 mL) was added to a solution of 1b (150 mg, 0.485 mmol) in CH2Cl2 (6 mL) under nitrogen atmosphere. The reaction mixture was stirred at room temperature for 2 hours. Phenylmagnesium bromide (1 M in tetrahydrofuran, 4 ml, 4.0 mmol) was dripped into the reaction mixture and the reaction mixture was stirred for 1.5 hours. The reaction mixture was quenched with water and then the mixture was washed with brine and CH2Cl2 for three times. The combined organic layers were dried over magnesium sulfate and then the solvents were evaporated under reduced pressure.

Synthesis of Compound NBNN-6
Boron tribromide (0.1 mL) was added to a solution of 1a (300 mg, 0.437 mmol) in CH2Cl2 (6 mL) under nitrogen atmosphere. The reaction mixture was stirred at room temperature for 2 hours. Isopropylmagnesium chloride (2 M in tetrahydrofuran, 2 ml, 4.0 mmol) was dripped into the reaction mixture and the reaction mixture was stirred for 1.5 hours. The reaction mixture was quenched with water and then the mixture was washed with brine and CH2Cl2 for three times. The combined organic layers were dried over magnesium sulfate and then the solvents were evaporated under reduced pressure.
Purification of the crude product by alumina column chromatography (petroleum ether/ethyl acetate = 20:1). Although we saw yellow product spots on both silica plate and alumina plate, we did not get the stable product NBNN-6 by column chromatography.

Synthesis of Compound NBNN-7
Boron tribromide (0.1 mL) was added to a solution of 1a (100 mg, 0.157 mmol) in CH2Cl2 (2 mL) under nitrogen atmosphere. The reaction mixture was stirred at room temperature for 2 hours. Methyl lithium diethyl ether (1.6 M in diethyl ether, 2.5 ml, 4.0 mmol) was dripped into the reaction mixture and the reaction mixture was stirred for 1.5 hours. The reaction mixture was quenched with water and then the mixture was washed with brine and CH2Cl2 for three times. The combined organic layers were dried over magnesium sulfate and then the solvents were evaporated under reduced pressure.
Purification of the crude product by alumina column chromatography (petroleum ether/ethyl acetate = 25:1). Although we saw orange product spots on both silica plate and alumina plate, we did not get the stable product NBNN-7 by column chromatography.

Synthesis of Compound NBNN-8
Boron tribromide (0.1 mL) was added to a solution of 1a (300 mg, 0.437 mmol) in CH2Cl2 (6 mL) under nitrogen atmosphere. The reaction mixture was stirred at room temperature for 2 hours. Vinylmagnesium bromide (2 M in tetrahydrofuran, 2 ml, 4.0 mmol) was dripped into the reaction mixture and the reaction mixture was stirred for 1.5 hours. The reaction mixture was quenched with water and then the mixture was washed with brine and CH2Cl2 for three times. The combined organic layers were dried over magnesium sulfate and then the solvents were evaporated under reduced pressure.
We saw lighter orange product spots on both silica plate and alumina plate, but we did not get the stable product NBNN-8 by column chromatography.
After quenching with triethylamine, the reaction mixture was concentrated under reduced pressure. Purification of the crude product by alumina column chromatography (petroleum ether/ethyl acetate = 20:1) afforded the product NBNN-1f as a red solid in 78% yield (56 mg, 0.078 mmol), which was confirmed by X-ray diffraction analysis.
After quenching with triethylamine, the reaction mixture was concentrated under reduced pressure. Purification of the crude product by alumina column chromatography (petroleum ether/ethyl acetate = 20:1) afforded the product NBNN-2f as a red solid in 58% yield (
After quenching with triethylamine, the reaction mixture was concentrated under reduced pressure. Purification of the crude product by alumina column chromatography(petroleum ether/ethyl acetate = 4:1) afforded the mixed product NBNN-4f as a red solid. We found that the stability of product NBNN-4f was not good, so we did not get clean NMR spectrum ( Figure

Electrochemical Properties
Electrochemical measurements were through a three-elecyrode system with a glassy carbon work electrode, a Pt wire reference electrode and a Pt wire counter electrode. NBNN-1, NBNN-3, NBNN-4, NBNN-1f, NBNN-2f, and 1a were measured in CH3CN (0.1 mol/L n Bu4NBF4 vs Fc/Fc + ) at a scan rate of 100 mV/s. The solubility of NBNN-2 in CH3CN is not good, so it was measured in CH2Cl2 (0.1 mol/L n Bu4NBF4 vs Fc/Fc + ) at a scan rate of 100 mV/s. No obvious peak can be found of NBNN-5 and 1b in either CH3CN or CH2Cl2.

Computational Results
All calculations were performed using the Gaussian 16 suite of programs. 3 . Initial input coordinates were taken from the corresponding crystal structure data if applicable, while all others were generated in GausView 6.0. DFT and TD-DFT calculations were performed using the B3LYP/6-311g(d,p) level 4 of theory based on optimized structures.       Figure S5.1 Fluorescence spectra in PMMA(10 wt%) film

X-ray Crystallographic Analysis
Crystals of NBNN-1 and NBNN-1f were grown by mixed solution of CH2Cl2 and petroleum ether. The crystal data were collected on a Bruker SMART APEX-II diffractometer at 296.15 K. Crystal of NBNN-3 was grown by mixed solution of ethyl acetate and petroleum ether. The crystal data were collected on a Bruker SMART APEX-II diffractometer at 180.00 K. The crystal data of NBNN-1, NBNN-1f and NBNN-3 have been deposited at the Cambridge Crystallographic Data Center (CCDC).