Abstract
We report on the synthesis as well as the optical, electrochemical and morphological properties of two polyrotaxanes (4a and 4b), which consist of electron-accepting 9,9-dicyanomethylenefluorene 1 as an inclusion complex in persilylated β- or γ-cyclodextrin (TMS-β-CD, TMS-γ-CD) (1a, 1b) and methyltriphenylamine as an electron-donating molecule. They are statistically distributed into the conjugated chains of 9,9-dioctylfluorene 3 and compared with those of the corresponding non-rotaxane 4 counterpart. Rotaxane formation results in improvements of the solubility, the thermal stability, and the photophysical properties. Polyrotaxanes 4a and 4b exhibited slightly red-shifted absorption bands with respect to the non-rotaxane 4 counterpart. The fluorescence lifetimes of polyrotaxanes follow a mono-exponential decay with a value of τ = 1.14 ns compared with the non-rotaxane, where a bi-exponential decay composed of a main component with a relative short time of τ1 = 0.88 (57.08%) and a minor component with a longer lifetime of τ2 = 1.56 ns (42.92%) were determined. The optical and electrochemical band gaps (ΔEg) as well as the ionization potential and electronic affinity characterized by smaller values compared to the values of any of the constituents. AFM reveals that the film surface of 4a and 4b displays a granular morphology with a lower dispersity supported by a smaller roughness exponent compared with the non-rotaxane counterpart.
Highlights
Semiconducting π-conjugated polymers have attracted attention in the last years as promising active hole-transporting materials, which have a wide range of applications in electro-optical devices [1,2,3,4]
Due to lower tendency to aggregate formations of functionalized CDs [31], polyrotaxanes with permodified CDs are characterized by a better solubility in common organic solvents, a higher fluorescence efficiency, a higher transparency of the solid films, and an easier processability compared with native CDs
To clarify whether the guest molecule 1 can be accommodated inside the permodified CDs cavities, the approximated stability constant (Ks) was investigated
Summary
Semiconducting π-conjugated polymers have attracted attention in the last years as promising active hole-transporting materials, which have a wide range of applications in electro-optical devices [1,2,3,4]. Recently reported results have shown improvements of the thermal stability, solubility, luminescence and surface characteristics of polyrotaxanes compared to those of non-rotaxane counterparts [8,13,19,20,21,22,23,24,25] This approach has been applied for the synthesis of polyrotaxanes by incorporating chemically modified CDs as host molecules [11,26,27,28,29,30]. The combination of D–A units associated with the encapsulation of an acceptor monomer into CDs has been successfully employed for the fabrication of PFs materials with smaller optical and electrochemical band gaps [13]. We report on the synthesis as well as the characterization of the optical, electrochemical and morphological properties of 4a and 4b polyrotaxanes, which consist of 1a or 1b and 2 units statistically distributed into the conjugated chains of 3 and compared them with those of the corresponding 4 nonrotaxane counterpart (Figure 1)
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