Abstract
Two alternating polyfluorene polyrotaxanes (3.TM-beta CD and 3.TM-gamma CD) have been synthesized by the coupling of 2,7-dibromofluorene encapsulated into 2,3,6-tri-O-methyl-beta-or.-cyclodextrin (TM-beta CD, TM-gamma CD) cavities with 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester. Their optical, electrochemical and morphological properties have been evaluated and compared to those of the non-rotaxane counterpart 3. The influence of TM-beta CD or TM-gamma CD encapsulation on the thermal stability, solubility in common organic solvents, film forming ability was also investigated. Polyrotaxane 3.TM-beta CD exhibits a hypsochromic shift, while 3.TM-gamma CD displays a bathochromic with respect to the non-rotaxane 3 counterpart. For the diluted CHCl3 solutions the fluorescence lifetimes of all compounds follow a mono-exponential decay with a time constant of approximate to 0.6 ns. At higher concentration the fluorescence decay remains mono-exponential for 3.TM-beta CD and polymers 3, with a lifetime tau = 0.7 ns and 0.8 ns, whereas the 3.TM-gamma CD polyrotaxane shows a bi-exponential decay consisting of a main component (with a weight of 98% of the total luminescence) with a relatively short decay constant of tau(1) = 0.7 ns and a minor component with a longer lifetime of tau(2) = 5.4 ns (2%). The electrochemical band gap (.Eg) of 3.TM-beta CD polyrotaxane is smaller than that of 3.TM-gamma CD and 3, respectively. The lower.Eg value for 3.TM-beta CD suggests that the encapsulation has a greater effect on the reduction process, which affects the LUMO energy level value. Based on AFM analysis, 3.TM-beta CD and 3.TM-gamma CD polyrotaxane compounds exhibit a granular morphology with lower dispersity and smaller roughness exponent of the film surfaces in comparison with those of the neat copolymer 3.