The effect of the macrocyclic encapsulation on the photophysical properties of conjugated polymers

We report the effect of the macrocyclic encapsulation on the photophysical properties of poly(9,9-dioctylfluorene-alt-bithiophene) polyrotaxanes copolymers. The encapsulated compounds were synthesized by Suzuki cross-coupling reaction between 5,5'-dibromo-2,2'-bithiophene (DBT) inclusion complexes in randomly methylated β-cyclodextrin (RM-βCD), 2,3,6-tri-O-methyl β-cyclodextrin (TM-βCD), 2,3,6-tri-O-trimethylsilyl β-cyclodextrin (TMS-βCD) or cucurbit[7]uril (CB7) with a bulky 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester (DF) as stoppers. These supramolecular compounds exhibited distinct improvement in the solubility, molecular weight, film forming ability, surface-morphological characteristics and reduced aggregation tendency compared to those of the neat compound. Also, the threading of conjugated backbones into macrocycles leads to an increasing environmental stability and resistance to quenching from impurities. Fluorescence emission (PL) shows vibronic transitions and a mono-exponential kinetics. The electrochemical data provided that the investigated compounds exhibited n- and p-doping processes. The encapsulation of DBT into TM-βCD or TMS-βCD cavities exhibits a greater effect on the LUMO, while the encapsulation into CB7 affects the HOMO energy levels. The HOMO/LUMO energy levels indicate that the investigated polyrotaxanes are electrochemically accessible as electron-transporting materials in electronic devices. Based on AFM analysis, polyrotaxane compounds exhibits a higher tendency to organize into fibers or linear ribbons.