An ambient stable core-substituted perylene bisimide dianion: isolation and single crystal structure analysis

The reduction of a highly electron deficient PBI afforded the corresponding dianion disodium salt that was characterized by single crystal structure analysis.


Materials and Methods
Starting material Cl 4 PBA was purchased from SYNTHON Chemicals and its purity was carefully checked by NMR and HRMS. DBI was synthesized according to literature known procedure. S1 Column chromatography was performed on silica gel (particle size 0.040−0.063 mm). All other commercially available reagents and solvents were of reagent grade and used without further purification. The solvents for the spectroscopic measurements and other experiments were of spectroscopic grade and used without further purification. UV-Vis absorption spectra were recorded on a Perkin Elmer Lamda 950 spectrometer. Steady-state fluorescence spectra were recorded under ambient conditions on a PTI QM4-2003 fluorescence spectrometer and corrected against photomultiplier and lamp intensity. The fluorescence quantum yields were determined by optical dilute method S2 (A < 0.05) using N,N´-di(2,6-diisopropylphenyl)-perylene-3,4:9,10tetracarboxylic acid bisimide (φ fl = 1.00 in chloroform) as reference. NMR spectra were recorded on a Bruker DMX 400 spectrometer. 13 C NMR spectra were broad-band proton-decoupled ( 13 C{ 1 H}). Chemical shifts () are listed in parts per million (ppm) and are reported relative to tetramethylsilane. Coupling constants (J) are quoted in Hertz (Hz). Spectra are referenced internally to residual proton solvent resonances or natural-abundance carbon resonances. IR spectra were recorded on a JASCO FT/IR-4100 spectrometer using an ATR unit. MALDI-TOF mass spectra were recorded on a Bruker Daltronik GmbH (autoflex II) mass spectrometer. High resolution ESI-TOF mass spectrometry was carried out on a microTOF focus instrument (Bruker Daltronik GmbH). For cyclic and square wave voltammetry, a standard commercial electrochemical analyzer (EC epsilon; BAS Instruments, UK) with a three electrode singlecompartment cell was used. The supporting electrolyte tetrabutylammonium hexafluorophosphate (TBAHFP) was recrystallized from ethanol/water. The measurements were carried out using ferrocene/ferrocenium (Fc/Fc + ) as an internal standard for the calibration of the potential.
Ag/AgCl reference electrode was used. A Pt disc and a Pt wire were used as working and auxiliary electrodes, respectively. The set-up for spectroelectrochemistry consists of a cylindrical quartz cell with an optically transparent and polished bottom, a platinum disc working electrode (6 mm diameter), a gold-coated metal plate as counter electrode and an Ag/AgCl pseudoreference electrode. An EG & G Princeton Applied Research Model 283 potentiostat was used.
UV/vis spectra (JASCO V-670 UV/vis/NIR spectrometer) were recorded in reflection at the polished working electrode, with 100 μm distance between the cell bottom and the surface of the working electrode (adjusted with a micrometer screw). Elemental analyses were performed with an Elementar vario micro cube. DFT calculations for a simplified structure of PBI dianion 4 (fluorinated alkyl chains were replaced by methyl groups and sodium cations are omitted) were performed by using the Gaussian 09 program package S3 with B3-LYP S4 as functional and 6-31+G* as basis set. The structures were geometry optimized, followed by frequency calculations on the optimized structures which confirmed the existence of a minimum. For the starting geometry, the coordinates of the single crystal structure analysis were used. The HOMO of the PBI dianion shown in Scheme 1 (main text) was simulated with the help of the GaussView 5 visualization software package S5 using the data obtained from DFT calculations.

Br 4 Cl 4 PBI 2
A solution of 1.00 g (1.12 mmol) Cl 4 PBI 1 and 1.12 g (3.92 mmol) DBI in 40 mL of Oleum (20% SO 3 ) was stirred for 18 h at 100 °C. After cooling to room temperature the mixture was poured slowly onto 150 g of ice. 150 mL water were added and the precipitate was collected by filtration, washed several times with water and dried in vacuum. The crude product was purified by column chromatography using dichloromethane as the eluent to give a red solid. Mp.: >300 °C.

CN 4 Cl 4 PBI 3
Synthesis was carried out similar to a literature known procedure. S7 300 mg (248 µmol) Br 4 Cl 4 PBI 2 and 133 mg (1.49 mmol) copper cyanide were mixed in 15 mL of dry DMF under argon and heated to 140 °C for 2.5 h. After cooling to room temperature the mixture was poured onto 150 mL of water. The precipitate was filtered off, washed with water and dissolved in dichloromethane. The solution was dried over MgSO 4 and concentrated under reduced pressure. The crude product was purified several times by column chromatography (silica, dichloromethane/ethyl acetate (95/5)) to give an orange-red solid.

Single crystal data
Single crystals suitable for X-ray diffraction experiments were grown by slow diffusion of pentane into a 1mM solution of 4 in acetone at room temperature.
Crystal Data were collected on a Bruker D8Quest Kappa Diffractometer using CuKα-radiation from an Incoatec IµS microsource with Montel multi layered mirror, a Photon100 CMOS detector and Apex2 software at 100K. The structure was solved using direct methods (SHELXS), expanded with Fourier techniques and refined with SHELXL. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in the structure factor calculation on geometrically idealized positions.         Quaternary carbon atoms and CF 2 , CF 3 groups could not be detected.