Aromatic Co-Polyazomethine\nPolyrotaxane with Enhanced\nSolubility Applied as a Hole Carrier in a p–n Heterojunction\nDiode

Conjugated coazomethine <b>4</b> and the polyrotaxane <b>4·TMe-βCD</b> were synthesized by Suzuki coupling of\nbromine-terminated bis-azomethine <b>1</b> and its encapsulated\nform <b>1·TMe-βCD</b> with 9,9-dioctylfluorene-2,7-diboronic\nacid bis(1,3-propanediol) ester <b>2</b>, followed by the end-capping\nwith 3-bromothiophene <b>3</b>. FT-IR and <sup>1</sup>H NMR\nspectroscopies proved the chemical structures of <b>4</b> and <b>4·TMe-βCD</b>. Polyrotaxane formation improves solubility,\nfilm-forming ability, adhesivity onto different substrates, and thermal\nstability. The result of 2,3,6-tri-<i>O</i>-methyl-β-cyclodextrin\n(TMe-βCD) encapsulation was evidenced by higher fluorescence\n(Φ<sub>FL</sub>), phosphorescence (Φ<sub>Ph</sub>), lifetime\n(τ), reversible electrochemical reduction, or better self-organization\nof <b>4·TMe-βCD</b>. Doping of <b>4</b> and <b>4·TMe-βCD</b> by exposure to iodine was found to increase\nthe electrical conductivities up to 1 × 10<sup>–7</sup> S·cm<sup>–1</sup>. Owing to <b>4·TMe-βCD</b> has better photophysical properties, the hole-transporting capability\nwas explored for the first time in a hybrid p–n heterojunction\ndiode. The measured current–voltage characteristics of the\neGaIn/<b>4·TMe-βCD</b>/ZnO/Al/ZnO diode revealed\na rectification ratio of 56 at ±3 V and saturation current of\n0.46 mA, highlighting the ambipolar characteristics of <b>4·TMe-βCD</b>, which poses both p- and n-type doping features. These findings\nare relevant for a better understanding of the hole-transporting ability\nof supramolecular semiconductor materials with a wide range of applications\nin optoelectronics.