Synthesis and photophysical characteristics of polyfluorene polyrotaxanes.

ABSTRACT: Two alternating polyfluorene polyrotaxanes (3·TM-?CD and 3·TM-?CD) have been synthesized by the coupling of 2,7-dibromofluorene encapsulated into 2,3,6-tri-O-methyl-?- or ?-cyclodextrin (TM-?CD, TM-?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-?CD or TM-?CD encapsulation on the thermal stability, solubility in common organic solvents, film forming ability was also investigated. Polyrotaxane 3·TM-?CD exhibits a hypsochromic shift, while 3·TM-?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 ?0.6 ns. At higher concentration the fluorescence decay remains mono-exponential for 3·TM-?CD and polymers 3, with a lifetime ? = 0.7 ns and 0.8 ns, whereas the 3·TM-?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 ?1 = 0.7 ns and a minor component with a longer lifetime of ?2 = 5.4 ns (2%). The electrochemical band gap (?E g ) of 3·TM-?CD polyrotaxane is smaller than that of 3·TM-?CD and 3, respectively. The lower ?E g value for 3·TM-?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-?CD and 3·TM-?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.

SUBMITTER: Farcas A 

PROVIDER: S-EPMC4734422 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature