Increasing and Dispersing Strain in Pyrene-Fused Azaacenes

A new strategy to obtain distorted pyrene-fused azaacenes is reported. The careful alignment and selection of substituents give rise to highly twisted pyrene-fused azaacenes. A combined global and local theoretical analysis shows how the strain is generated and dispersed across the aromatic backbone. Furthermore, simulation of the observed optoelectronic properties shines light on the structural factors that govern the properties of twisted pyrene-fused azaacenes.

The HOMO-1 and HOMO orbitals show density on both quinoxaline residues of 12 and 13, but in the case of 14, the electronic densities are localized in opposite quinoxaline residues in the HOMO-1 and HOMO, respectively. Also, while in the case of 12 and 13, the LUMO and LUMO+1 densities are almost identical, but in the case of 14 LUMO and the LUMO+1 are exchanged.

S1. General Experimental Methods
All reagents and solvents were purchased from Fisher Scientific, ABCR, Alfa Aesar, Sigma Aldrich or VWR, and were used without further purification unless specified otherwise. Preparation of air moisture sensitive materials was carried out in flamed-dried flasks under nitrogen atmosphere employing standard Schlenk techniques. Anhydrous THF was dried using an Innovative Pure Solve solvent purification system. Commercial chlorotriisopropylsilane was dried by distillation under reduced pressure and stored with molecular sieves under argon atmosphere in a freezer until its use.
Column chromatography was performed on Silica gel 60 (40-60 μm) from Scharlab, employing petroleum ether and dichloromethane as eluents. Analytical thin layer chromatography (TLC) was carried out using aluminum sheets (20x20 cm) pre-coated with silica gel RP-18W 60 F254 from Merck). UV-active compounds were detected using a UV-lamp from CAMAG at wavelength λ = 254 or 366 nm. NMR spectra in solution were recorded on a Bruker Avance 400 MHz or 500 MHz spectrometer at 298K using partially deuterated solvents as internal standards. X-ray data collections were performed in an Agilent Supernova diffractometer equipped with an Atlas CCD area detector, and a CuKα micro-focus source with multilayer optics (λ = 1.54184Å, 250μm FWHM beam size) by Dr. Leire Sanfelices (SGiker, University of the Basque Country). The quality of the crystals was checked under a polarizing microscope, and a suitable crystal or fragment was mounted on a Mitegen Micromount TM using Paratone-N inert oil and transferred to the diffractometer. Samples were kept at 150(10)K with an Oxford Cryosystems Cryostream 700 cooler.
Absorption spectra were recorded on a Perkin-Elmer Lambda 950 spectrometer.
Fluorescence spectra were recorded on a LS55 Perkin-Elmer Fluorescence spectrometer.
Electrochemical measurements were carried out on a Princeton Applied Research Parstat 2273 in a 3-electrode single compartment cell with glassy-carbon disc working electrode (φ = 3mm), a platinum wire counter electrode (φ = 0.5mm) and a silver wire pseudoreference electrode. The cell and the electrodes were custom made. All the potential values are reported versus the redox potential of the ferrocene/ferrocenium couple.

S15
Preparation of starting materials.
In a round bottom flask 360 mg (0.404 mmol) of 4 and 257 mg of sodium carbonate (2.43 mmol, 6 eq.) were suspended on 10 mL of chloroform and cooled below 0°C, then 1 mL of a solution 1.62M of bromide (3.1 g/mL, 4 eq.) in chloroform was slowly added. After 15 minutes the reaction was stopped. More solvent was added, and the organic phase was treated with a 10% aqueous solution of sodium thiosulfate, then washed with water and brine, dried over sodium sulfate and filtered. Solvent was removed by rotary evaporation. Resulting crude was dissolved in 6 mL of a mixture 1:5 chloroform/acetonitrile and 442 mg of cerium-ammonium-nitrate 99% (CAN, 0.808 mmol, 2 eq.) was added. Reaction was heated up to 70 °C overnight. When reaction was completed dichloromethane was added, the organic phase was washed with water and brine, dried over sodium sulfate and filtered. Solvent was removed by rotary evaporation. Resulting crude was purified by flash chromatography (eluent mixture hexanes/DCM 9:1) affording 106 mg (0.189 mmol) of red solid 5 in 47% yield over two steps. ---7: 2,7-bis(triphenylsilyl)-pyrene-4,5,9,10-tetraone.
In a round bottom flask 210 mg (0.188 mmol) of 6 and 120 mg of sodium carbonate (1.13 mmol, 6 eq.) were suspended on chloroform and cooled below 0°C, then 1 mL of a 0.75M solution of bromide (3.1 g/mol, 4 eq.) in chloroform was slowly added. After 15 minutes the reaction was stopped. More solvent was added, and the organic phase was treated with a 10% aqueous solution of sodium thiosulfate, then washed with water and brine, dried over sodium sulfate and filtered. Solvent was removed by rotary evaporation. Resulting crude was dissolved in 6 mL of 1:5 mixture chloroform/acetonitrile and 206 mg of cerium-ammonium-nitrate 99% (0.376 mmol, 2 eq.) was added. Reaction was heated up to 70 °C overnight. When reaction was completed dichloromethane is added, the organic phase was washed with water and brine, dried over sodium sulfate and filtered. Solvent was removed by rotary evaporation. Resulting crude was purified by flash chromatography (eluent mixture hexanes/DCM 3:2) affording 60mg (0.0771 µmol) of red solid 7 in 45% yield over two steps. Crystals for 7 were obtained by chloroform evaporation. ---11: 3,6-bis((tris(trimethylsilyl)silyl)ethynyl)benzene-1,2-diamine.
In a two-neck 250 mL round bottom flask 500 mg (0.747 mmol) of 10 was dissolved in 35 mL of dry diethyl ether and cooled to −15°C, then under nitrogen atmosphere 300 mg (7.47 mmol, 10 eq.) of LiAlH4 was slowly added. Reaction was allowed to reach room temperature, after two hours was quenched with ammonium chloride and extracted with hexane. Organic phase was washed with water and brine, dried over sodium sulfate and solvent was removed by rotary evaporation. Trituration on methanol afforded 176 mg (0.26 mmol) of pale yellow solid 11 in 35% yield. In a Schlenk flask 13 mg of tetraketone 1 (36 µmol, 1 eq.) and 52 mg of diamine 11 (80 µmol, 2.2 eq.) were dissolved in little amount chloroform and 1.5 mL of acetic acid was added. Mixture was heated up to 40°C for three hours under nitrogen atmosphere. Reaction was cooled to room temperature. Chloroform was removed, methanol was added, and the suspension was filtered. In a Schlenk flask 20 mg of tetraketone 5 (34 µmol, 1 eq.) and 65 mg of diamine 11 (104 µmol, 3 eq.) were suspended in 1.5 mL of acetic acid. Mixture is heated up 40° for three hours under nitrogen atmosphere. Reaction was cooled to room temperature, methanol was added, and the suspension was filtered. Resulting solids were purified by flash chromatography (eluent mixture hexane/DCM 4:1). Desired product was isolated by precipitation on methanol affording 23.8 mg (14 µmol) of yellow solid 13 in 40% yield. Crystals were obtained by low vapor diffusion of ethanol over a toluene solution of 13.
In a Schlenk flask 20 mg of tetraketone 7 (26 µmol, 1 eq.) and 50 mg of diamine 11 (77 µmol, 3 eq.) were suspended in 3 mL of acetic acid. Mixture was heated at 40 °C for three hours under nitrogen atmosphere. Reaction was cooled to room temperature, methanol was added, and the suspension was filtered. Resulting solids were purified by flash chromatography (eluent mixture hexane/DCM 4:1). Desired product was isolated by precipitation on methanol affording 23.8 mg (12 µmol) of yellow solid 14 in 47% yield. Crystals were obtained by low vapor diffusion of ethanol over a toluene solution of 14.

S4. General Methods for Calculations
The geometries from the crystallographic data were first optimized in cartesian space to a very small gradient with the GFN2-xTB method (Geometry, Frequency, Non-covalent, Extended Tight-Binding) 5 and then they were optimized at the B3LYP-6-31G(d,p) level.

S4.1 Strain calculations
The strain energies for the three systems under consideration were estimated with a simplified H-capped molecular analogue where the bulky groups were deleted, the H-capping atoms optimized, and then the molecule allowed to relax.

H-capped molecules
Aromatic core Polycyclic core Acetylenes Quantum yields were calculated following the next equation: The error of was calculated as follows: To measure quantum yield of 12, 13 and 14, 9,10-Diphenylanthracene (DPA) was selected as reference standard (Φ ! /0' = 0.93) 6 at 7.57·10 -7 M in cyclohexane ( 1234 = 1.45). The excitation wavelength was set at 340 nm and three different solutions at different concentration of 12, 13 and 14 were analyzed.
Figure S17 13 C NMR on CDCl3 of compound 6.