Aromatic Co-Polyazomethine Polyrotaxane with Enhanced Solubility Applied as a Hole Carrier in a p–n Heterojunction Diode

Conjugated coazomethine 4 and the polyrotaxane 4·TMe-βCD were synthesized by Suzuki coupling of bromine-terminated bis-azomethine 1 and its encapsulated form 1·TMe-βCD with 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester 2, followed by the end-capping with 3-bromothiophene 3. FT-IR and 1H NMR spectroscopies proved the chemical structures of 4 and 4·TMe-βCD. Polyrotaxane formation improves solubility, film-forming ability, adhesivity onto different substrates, and thermal stability. The result of 2,3,6-tri-O-methyl-β-cyclodextrin (TMe-βCD) encapsulation was evidenced by higher fluorescence (ΦFL), phosphorescence (ΦPh), lifetime (τ), reversible electrochemical reduction, or better self-organization of 4·TMe-βCD. Doping of 4 and 4·TMe-βCD by exposure to iodine was found to increase the electrical conductivities up to 1 × 10–7 S·cm–1. Owing to 4·TMe-βCD has better photophysical properties, the hole-transporting capability was explored for the first time in a hybrid p–n heterojunction diode. The measured current–voltage characteristics of the eGaIn/4·TMe-βCD/ZnO/Al/ZnO diode revealed a rectification ratio of 56 at ±3 V and saturation current of 0.46 mA, highlighting the ambipolar characteristics of 4·TMe-βCD, which poses both p- and n-type doping features. These findings are relevant for a better understanding of the hole-transporting ability of supramolecular semiconductor materials with a wide range of applications in optoelectronics.