Anthracene and beta-Cyclodextrin Based Supramolecular Semi-Conducting Thin Film: Effect of the Encapsulation on the Optical and Electrical Properties

In this study, we describe the synthesis of a host-guest supramolecule (TDPAn beta-CD) formed from an anthracene-based conjugated molecule (TDPAn, guest) encapsulated in cyclodextrin (beta-CD, host) under microwave irradiation. The obtaining of the desired rotaxane was confirmed by different spectroscopic and thermal analyzes. A comparative study between the physicochemical and electrical properties of the free molecule (TDPAn) and those of the rotaxane (TDPAn beta-CD) was conducted. Thermal analyzes show an amorphous morphology and good thermal stability for the rotaxane. The surface morphology of the synthesized materials was studied using atomic force microscopy and contact angle measurement. The supramolecular film exhibits a smooth and homogeneous surface with a relatively low surface roughness compared to that of the free model. The absorption and photoluminescence spectra of the rotaxane thin film are blue-shifted in comparison with TDPAn, due to a steric hindrance effect of the beta-CD. Hence, a blue intense photoluminescence was emitted from the rotaxane layer, compared to a violet-red emission in the case of non-encapsulated TDPAn. Higher electron affinity and ionization potential for the host-guest supramolecule were observed by cyclic voltammetry. The static study of ITO/TDPAn/Al and ITO/TDPAn beta-CD/Al schottky single layer diodes showed typical behaviors with relatively low threshold voltages and higher charge carrier mobility was achieved for the rotaxane active layer.