The effect of permodified cyclodextrins encapsulation on the photophysical properties of a polyfluorene with randomly distributed electron-donor and rotaxane electron-acceptor units

Abstract

SummaryWe 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 (ΔE g) 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.

Synthesis and photophysical characteristics of polyfluorene polyrotaxanes

“…However, some major drawbacks for their use are their high ionization potential associated with low photoluminescence (PL) efficiency, their rather large band gap and facile photochemical degradation [ 12 – 13 ]. Different strategies have been employed in view to reduce these undesirable effects, e.g., the synthesis of copolymers [ 14 – 17 ], block copolymers [ 18 ], the introduction of donor (D) and acceptor (A) moieties [ 19 – 21 ], or bulky substituents at the C-9 position of the fluorene units [ 22 – 24 ], incorporating PF moieties into zeolites [ 25 ], nanochannels [ 26 ], or by wrapping with amylose [ 27 ]. The past decade has witnessed remarkable innovations and progress in polymer science, including the field of supramolecular science as a complementary field, which offers great opportunity for new concepts, new materials with unique properties, and novel practical applications.…”

Synthesis, Photophysical, and Morphological Properties of Azomethine‐Persylilated α‐Cyclodextrin Main‐Chain Polyrotaxane

“…[ 16,17,19,21,22 ] The use of permodifi ed CDs derivatives, which exhibit higher solubility in nonpolar organic solvents and lower propensity to aggregate formations [ 23,24 ] has been employed as an alternative supramolecular approach for the synthesis of polyrotaxanes with conjugated polymers. [25][26][27][28][29][30] Recently, permethylated αCD has been shown to produce PAMs main-chain polyrotaxanes with better solubility in common organic solvents and easier processability with respect to the nonrotaxane ones. [ 31 ] As a continuation of our previous studies, we decided to explore the effect of hexakis(2,3,6-trimethylsilyl) α-cyclodextrin (TMS-αCD), as an alternative approach to bring some benefi ts on the photophysical characteristics of PAMs.…”

“…The encapsulation into macrocyclic cavities, i.e., native cyclodextrins (CDs) of PAMs present noticeable advantages for optoelectronic applications, compared to those observed on nonrotaxane counterparts, due to easier processability and adhesivity on the substrates of solid films, as well as the improvements of morphological characteristics . The use of permodified CDs derivatives, which exhibit higher solubility in nonpolar organic solvents and lower propensity to aggregate formations has been employed as an alternative supramolecular approach for the synthesis of polyrotaxanes with conjugated polymers . Recently, permethylated αCD has been shown to produce PAMs main‐chain polyrotaxanes with better solubility in common organic solvents and easier processability with respect to the nonrotaxane ones .…”

Synthesis, Photophysics, and Langmuir Films of Polyfluorene/Permodified Cyclodextrin Polyrotaxanes

“…This efficient strategy, which does not require the formation of covalent bonds between hosts and guests, allows the optimization of the optical and electrical properties of PFs . The architectures of the polypseudorotaxane (PP) and polyrotaxane (PR) types present increased distances between the PF chains and are thus able to decrease their tendency to aggregate and enhance a broad range of photophysical properties. − Because of the significant interest in the potential applications of these supramolecular compounds, a relatively large number of PPs and PRs containing various macrocyclic molecules have been reported by several research groups. − The use of native cyclodextrins (CDs) as host molecules has been extensively investigated, and this approach has been employed to obtain a wide variety of supramolecular architectures. − The second group of investigated host molecules used in the synthesis of this type of supramolecular compounds is composed of randomly methylated β-CD, 2,3,6-tri- O -methyl β- or γ-CD (TMeCD), − and 2,3,6-tri- O -trimethylsilyl α-, β-, or γ-CD (TMS-CD). ,, At the same time, the hydrophobic permodified CDs surfaces are able to hinder the strong face-to-face π-interaction between conjugated backbones, which leads to a better tendency to organize into a smooth and homogeneous surface morphology in the solid state and a lower propensity to aggregate as opposed to native CDs . On the basis of our previous studies, alternating PF copolymers prepared from a 1:1 mol feed ratio of 2,7-dibromofluorene (DBF) encapsulated into native CDs or TMe-CDs and 9,9-dioctylfluorene-2,7-diboronic acid bis­(1,3-propanediol) ester (DOF) followed by end-capping with bromobenzene (Br-Ph) exhibited improved photophysical characteristics compared with their nonencapsulated counterparts.…”

“…14−19 The second group of investigated host molecules used in the synthesis of this type of supramolecular compounds is composed of randomly methylated β-CD, 20 2,3,6-tri-O-methyl βor γ-CD (TMeCD), 21−26 and 2,3,6-tri-O-trimethylsilyl α-, β-, or γ-CD (TMS-CD). 23,27,28 At the same time, the hydrophobic permodified CDs surfaces are able to hinder the strong face-to-face π-interaction between conjugated backbones, which leads to a better tendency to organize into a smooth and homogeneous surface morphology in the solid state 29 and a lower propensity to aggregate as opposed to native CDs. 30 On the basis of our previous studies, alternating PF copolymers prepared from a 1:1 mol feed ratio of 2,7dibromofluorene (DBF) encapsulated into native CDs 15 or TMe-CDs 24 and 9,9-dioctylfluorene-2,7-diboronic acid bis-(1,3-propanediol) ester (DOF) followed by end-capping with bromobenzene (Br-Ph) exhibited improved photophysical characteristics compared with their nonencapsulated counterparts.…”