Starting materials, if commercially available, were purchased and used as such. ZnO nanoparticles were purchased from Sigma Aldrich (Europe) (<100 nm particle size (DLS), <0 nm average particle size (APS), 20 wt % in H2O). 1H and 13C nuclear magnetic resonance (NMR) spectra were recorded at 300 and 75 MHz in CDCL3. Chemical shifts are reported in δ units, parts per million (ppm), and were measured relative to the signals for residual chloroform. Coupling constants (J) are given in Hertz (Hz). Multiplicities are abbreviated as follows: singlet (s), doublet (d), triplet (t), quartet (q), and multiplet (m). HRMS were recorded using TOF electrospray ionization (ESI-positive). IR spectra were recorded using FT-IR ATR, the solvents used were of spectroscopic or equivalent grade. Water was twice distilled and passed through a Millipore apparatus. All reaction mixtures were filtered through a 0.45 μm PTFE 25 mm syringe filter.
Synthesis of 4,4′-(Pyrrolo[3,2-b]pyrrole-1,4-diyl)dianiline (4)
Benzene-1,4-diamine 1 (2 mmol), 1.7% of Pt/Al2O3 (132.5 mg), 4.5% of ZnO nanoparticles (21.5 μL), and ethylene glycol (4 mL) were mixed manually inside a 50 mL quick-thread glass reaction tube. The tube was sealed with an Easy-On PTFE cap and put into a Carousel 12 Plus reaction station at 175 °C for 48 h. The reaction mixture was cooled to room temperature, and it needed to be opened carefully to depressurize the tube. After that, 25 mL of ethyl acetate was added, and the crude was filtered through a 0.45 μm PTFE filter. The reaction mixture was extracted with distilled water (3 × 10 mL), and the organic layer was dried with Na2SO4, filtered, and concentrated to afford the reaction crude that was checked by 1H-NMR. The crude reaction product was purified by chromatography (Silica gel, Hexane/Ethyl Acetate from 3:1 to 1:3 v:v) as a brown oil identified as the 4,4′-(pyrrolo[3,2-b]pyrrole-1,4-diyl)dianiline (4) (47 mg, yield 15%). 1H-NMR (300 MHz, Cl3CD); δ: 7.26 (d, J = 9 Hz, 4H), 6.95 (d, J = 3 Hz, 2H), 6.70 (d, J = 9 Hz, 4H), 6.27 (d, J = 3 Hz, 2H), 0.7 (sa,4H). 13C-NMR (75 MHz, Cl3CD); δ: 143.4(C), 133.2(C), 128.1(C), 121.3(CH), 121.1(CH), 116.1(CH), 93.6(CH). HRMS: [M + H+] calc. for C18H16N4: 289.1448; found: 289.14425. IR (ATR): 3771, 2922, 2851, 1632, 1516, 1421, 1273, 1177, 825, 689 cm−1. UV-vis (5 × 10−4 M in methanol): λmax 206, 240, and 298 nm.