Linear Oligofluorene-BODIPY structures for fluorescence applications

A family of linear oligofluorene-BODIPY structures, containing either a ter- or quaterfluorene unit, have been prepared, in which the attachment of the oligofluorene chain to the BODIPY unit is switched between the meso- and beta-positions. Each member of this family was investigated by UV-vis absorption and photoluminescence spectroscopy, cyclic voltammetry and thermal studies (TGA and DSC) to determine their suitability as emissive layers in hybrid luminescent devices. One candidate was then successfully deployed as a down converter to convert UV to visible light.


Contents
• Experimental procedures for new compounds

Experimental General experimental
Tetrakis(triphenylphosphine)palladium(0) (Pd(PPh 3 ) 4 ) was prepared prior to use and stored under nitrogen.Unless otherwise stated, all other reagents were sourced commercially and used without further purification.Dry solvents were obtained from a solvent purification system (SPS 400 from Innovative Technologies) using alumina as the drying agent. 1 H and 13 C NMR spectra were recorded on either a Bruker DRX 500 apparatus at 500.13 and 125.76 MHz, or a Bruker Avance DPX400 apparatus at 400.13 and 100.6 MHz.Chemical shifts are given in ppm; all J values are in Hz.Elemental analyses were obtained on a Perkin-Elmer 2400 analyser.MS LDI-TOF spectra were run on a Shimadzu Axima-CFR spectrometer (mass range 1-150000 Da).Accurate mass measurements (HRMS) were recorded using ASAP mode on an Orbitrap instrument at the EPSRC National Mass Spectrometry Service Centre in Swansea.Thermogravimetric analysis (TGA) was performed using a Perkin-Elmer Thermogravimetric Analyzer TGA7 under a constant flow of helium.Melting points were taken using a TA instruments DSC QC1000 Differential Scanning Calorimeter, or a Stuart Scientific apparatus, and are uncorrected.
Cyclic voltammetry (CV) measurements were performed on a CH Instruments 660A electrochemical workstation with iR compensation using anhydrous dichloromethane as the solvent.The electrodes were glassy carbon, platinum wire and silver wire as the working, counter and reference electrodes, respectively.All solutions were degassed (Ar) and contained monomer substrates in concentrations of ca. 10 -4 M, together with n-Bu 4 NPF 6 (0.1 M) as the supporting electrolyte.All measurements are referenced against the E 1/2 of the Fc/Fc + redox couple.Absorption spectra and CIE coordinates were recorded on a Unicam UV 300 instrument.
Photoluminescence measurements were recorded using a Perkin-Elmer LS 50 B fluorescence spectrometer in a quartz cuvette (path length 10 mm).For PLQY measurements, absorption and photoluminescence measurements were performed using a Jasco V-660 spectrophotometer and a Jasco FP 6500 spectroflurometer, respectively.
Electroluminescence (EL) measurements of the light-emitting diodes (LEDs) were carried out at room temperature using a Keithley source measure unit.The light was dispersed by an Oriel 1/8 m spectrograph before being collected by an Andor charge-coupled device.The UV LEDs (XSL 365 class) were purchased from Roithner Lasertechnik and were used with the glass lens removed.
Scheme 1: formation of the oligofluoreneboronic acids 11 -13.To a solution of 7'-bromo-9,9,9',9'-tetraoctyl-2,2'-bifluoren-7-yl) trimethylsilane (5) (8.957 g, 9.619 mmol) in dry tetrahydrofuran (100 mL), n-BuLi (1.95 M solution in n-hexanes, 6.41 mL, 12.51 mmol) was added dropwise under a N 2 atmosphere at -80 °C over the span of 2 min.The system was stirred at -80 °C for 10 min and then cooled down to -100 °C.Triisopropylborate (6.7 mL, 28.86 mmol) was added and the reaction mixture was allowed to warm up to room temperature and stirred for 18 h.The reaction mixture was washed with water (500 mL), and extracted with diethyl ether (4 x 100 mL).The combined organic fractions were washed with water (300 mL), dried over anhydrous MgSO 4 and the solvent evaporated to yield 8.587 g of crude product.The residue was purified by flash chromatography on a silica gel column with elution first by toluene to remove by-products and then with diethyl ether to recover the product as a white foamy solid (5.940 g, 6.63 mmol, 69 %); To a solution of 2-bromo-9,9,9',9',9'',9''-hexaoctyl-2,2'-terfluorenyl-7-trimethylsilane (6) (8 g, 5.73 mmol) in dry tetrahydrofuran (170 mL), n-BuLi (2.39 M solution in n-hexanes, 3.11 mL, 7.446 mmol) was added dropwise under a N 2 atmosphere at -80 °C over the span of 2 min.The system was stirred at -80 °C for 45 min and then cooled down to -100 °C.Triisopropylborate (4 mL, 17.85 mmol) was added and the reaction mixture was allowed to warm up to room temperature and stirred for 18 h.The reaction mixture was washed with water (500 mL) and extracted with diethyl ether (3 x 300 mL).The combined organic fractions were washed with water (500 mL), dried over anhydrous MgSO 4 and the solvent evaporated to yield a yellow crude product.
It was purified by flash chromatography on a silica gel column with elution first by toluene to remove byproducts and then with diethyl ether to recover the product as a white foamy solid ( A solution of 2,7-dibromo-9,9-dioctylfluorene 1 (19.740g, 36 mmol) and Pd(PPh 3 ) 4 (0.416 g, 0.36 mmol) in dry toluene (40 mL) was stirred under a N 2 atmosphere for 20 min.A solution of 9,9-dioctyl-7-trimethylsilylfluoren-2-ylboronic acid (2) (6.05 g, 12 mmol) in dry toluene (20 mL) was added to the mixture.The flask previously containing 2 was washed with an additional portion of dry toluene (20 mL) and added to the reaction mixture.
Triisopropylborate (3 mL, 13 mmol) was added and the reaction mixture was allowed to warm up to room temperature and stirred for 18 h.The reaction mixture was washed with water (500 mL), acidified with HCl until a pH of 2-3 was reached and extracted with diethyl ether (4 x 100 mL).The combined organic fractions were washed with water (300 mL), dried over anhydrous MgSO 4 and the solvent evaporated to yield 3.784 g of crude product.The residue was purified by flash chromatography on a silica gel column with elution first by toluene to remove by-products and then with diethyl ether to recover the product as a white foamy solid (3.05 g, 3.70 mmol, 85 %); Synthesis of 9,9,9',9',9'',9''-hexaoctyl-2,2'-terfluoren-7-ylboronic acid 12 To a solution of 7-bromo-9,9,9',9',9'',9''-hexaoctyl-2,2'-terfluorene (9) (1.701 g, 1.36 mmol) in dry tetrahydrofuran (20 mL), was added dropwise n-BuLi (2.5 M solution in n-hexanes, 0.7 mL, 1.79 mmol) under a N 2 atmosphere at -80 °C over the span of 2 min.The system was stirred at -80 °C for 45 min and then cooled down to -100 °C.Triisopropylborate (1 mL, 4.15 mmol) was added and the reaction mixture was allowed to warm up to room temperature and stirred for 18 h.The reaction mixture was washed with water (300 mL), acidified with HCl until a pH of 2-3 was reached and extracted with diethyl ether (7 x 100 mL).The combined organic fractions were washed with water (300 mL), dried over anhydrous MgSO 4 and the solvent evaporated to yield a yellow crude product.It was purified by flash chromatography on a silica gel column with elution first by toluene to remove by-products and then with diethyl ether to recover the product as a white foamy solid To a solution of 7-bromo-9,9,9',9',9'',9'',9''',9'''-octaoctyl-2,2'-quaterfluorene (10) (0.406 g, 0.25 mmol) in dry tetrahydrofuran (6 mL), was added dropwise n-BuLi (2.45 M solution in n-hexanes, 0.15 mL, 0.32 mmol) under a N 2 atmosphere at -80 °C.The system was stirred at -80 °C for 45 min and cooled down to -100 °C.
Triisopropylborate (0.2 mL, 0.75 mmol) was added and the reaction mixture was allowed to warm up to room temperature and stirred for 18 h.The reaction mixture was washed with water (200 mL), acidified with HCl until a pH of 2-3 was reached and extracted with diethyl ether (5 x 100 mL).The combined organic fractions were washed with water (200 mL), dried over anhydrous MgSO 4 and the solvent evaporated to yield 0.472 g of a white solid.The crude product was purified by flash chromatography on a silica gel column with elution first by toluene to remove by-products and then with diethyl ether to recover the product as a white foamy solid (0.37 g, 0.23 mmol, 73 %); Figure S1: oxidation wave of meso-TFBOD • Figure S2: reduction wave of meso-TFBOD • Figure S3: oxidation wave of meso-QFBOD • Figure S4: reduction wave of meso-QFBOD • Figure S5: oxidation wave of beta-TFBOD • Figure S6: reduction wave of beta-TFBOD • Figure S7: oxidation wave of beta-QFBOD • Figure S8: reduction wave of beta-QFBOD • Figure S9: UV-vis absorbance spectra used to calculate PLQY for meso-QFBOD • Figure S10: photoluminescence spectra used to calculate PLQY for meso-QFBOD • Figure S11: DSC plot for meso-TFBOD • Figure S12: electroluminescence spectrum of UV LED coated with meso-QFBOD Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C This journal is © The Royal Society of Chemistry 2013

Figure S12 :
Figure S12: spectrum of the uncoated LED subtracted from the spectrum of the meso-QFBOD coated LED (blue dashed line) compared to the spectrum of the coated LED (red line).
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C This journal is © The Royal Society of Chemistry 2013The flask previously containing 3 was washed with an additional portion of dry toluene (40 mL) and added to the reaction mixture.An aqueous 2M solution of Na 2 CO 3 (12.96mL, 25.92 mmol) was added and the system was stirred under N 2 refluxing at 80 °C for 18 h.The reaction mixture was washed with water (200 mL) and extracted with dichloromethane (5 x 200 mL).The combined organic fractions were washed with water (300 mL), dried over anhydrous MgSO 4 and the solvent evaporated yielding the crude product (30.180g)as a yellow oil.The residue was purified by column chromatography on silica gel eluting with petroleum ether and then crystallised in acetone to afford the product as a white crystalline solid (10.976 g, 8.014 mmol, 74 %); m.p.
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C This journal is © The Royal Society of Chemistry 2013 silica plug to remove polar by-products and crystallised from acetone to yield the product as a white crystalline in dichloromethane (56 mL), CF 3 COOH (1.8 mL) was added and the mixture stirred at room temperature for 2 h.Basic work up was carried out with water (2 x 100 mL), saturated NaHCO 3 solution (2 x 70 mL) and final washing with water (100 mL).The organic fraction was dried over anhydrous MgSO 4 and filtered through a Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C This journal is © The Royal Society of Chemistry 2013