Anthracene and β-cyclodextrin-based semi-conducting rotaxanes: Effect of the benzylation on the physico-chemical and electrical properties

In this work, we report the benzylation of an anthracene and β-Cyclodextrin-based rotaxane. Then, a comparative study between the physicochemical and electrical properties of the modified rotaxane (R-Bn) and those of the pristine supramolecule (R) was conducted. We noted an important improvement of the solubility of the rotaxane following the o-benzylation of the β-Cyclodextrin hydroxyl groups. The analysis of the surface topography of the rotaxane films using atomic force microscopy (AFM) showed a smoother surface morphology for the supramolecular assembly R-Bn. Also, we have demonstrated that the introduction of benzyl moieties induces a remarkable broadening and a bathochromic shift of the UV–visible absorption and photoluminescence spectra, an improvement in the fluorescence yield as well as a reduction of the optical and electrochemical band gaps. In addition, a white photoluminescence was emitted from R-Bn thin layer while a blue emission was observed in the case of the primitive rotaxane film (R). Regarding the electrical measurements, the benzylation of the rotaxane induced a dramatic decrease of the threshold voltage (from 3.70 V to 1.55 V) and the dynamic resistances (from 113.84 kΩ to 11.51 kΩ), an important increase by one order of magnitude of the charge carrier mobility and a drastic increase of the conductivity by 5 orders of magnitude.