Effect of Rotaxane Formation on the Photophysical, Morphological, and Adhesion Properties of Poly[2,7-(9,9-dioctylfluorene)-alt- (5,5’-bithiophene)] Main-Chain Polyrotaxanes a Aurica Farcas,* Indrajit Ghosh, Vasile C. Grigoras, Iuliana Stoica, Cristian Peptu, Werner M. Nau* Introduction Conjugated polymers have received considerable attention due to their potential applications in molecular electronics, such as light emitters, [1] organic transistor materials, [2] photovoltaic devices, [3] and in non-linear optics. [4] Among the conjugated polymers, in particular, a number of fluorene-based polymers (PFs) have attracted great interest as very promising candidates for organic light- emitting diodes (LEDs) due to their efficient and pure blue luminescence properties. [5–9] However, in view of the known difficulty of structural modifications of the polyfluorenes, [10] recent studies have focused on fluorene-based copolymers as an alternative approach to fine-tune their photophysical properties. [11–13] Among them, fluorene-thiophene or bithio- phene copolymers have gained special attention because of their excellent stability and wide electronic tunability by side chain modifications. [10] For example, it has recently been reported that the optical, electrochemical and thermal properties of fluorene/thiophene or bithiophene copolymers can be modified by differential substitution. Unfortunately, different structural regioregularities, especially when the bithiophene unit is present in the copolymer chain, can lead to undesirable side effects, such as a decrease in the fluorescence quantum yield. [10] Full Paper A. Farcas, V. C. Grigoras, I. Stoica, C. Peptu ‘‘Petru Poni’’, Institute of Macromolecular Chemistry, 700487 Iasi, Romania E-mail: auricafarcas@yahoo.com I. Ghosh, W. M. Nau Jacobs University, School of Engineering and Science, D-28759 Bremen, Germany E-mail: w.nau@jacobs-university.de a Supporting Information is available from the Wiley Online Library or from the author In order to investigate the effect of rotaxane formation on the photophysical and morpho- logical properties of p-conjugated materials, a new main chain polyrotaxane was synthesized through Suzuki coupling between the inclusion complex of 5,5’-dibromo-2,2’-bithiophene with randomly methylated b-cyclodextrin and 9,9-dioctylfluorene-2,7-trimethylene diborate. Due to rotaxane formation, a blue shift in the absorption spectra as well as in the fluorescence spectra was observed, while the fluor- escence quantum yields and fluor- escence lifetimes remained unchanged. This study demonstrates that rotaxane formation can alter the electronic and morphological properties of the threaded copolymer, which is of great interest for electronic applications. 1022 Macromol. Chem. Phys. 2011, 212, 1022–1031 ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/macp.201000727