We report the effect of the macrocyclic encapsulation on the photophysical properties of poly(9,9-dioctylfluorene-alt-bithiophene) polyrotaxanes copolymers. The encapsulated compounds were synthesized by Suzuki cross-coupling reaction between 5,5'-dibromo-2,2'-bithiophene (DBT) inclusion complexes in randomly methylated β-cyclodextrin (RM-βCD), 2,3,6-tri-O-methyl β-cyclodextrin (TM-βCD), 2,3,6-tri-O-trimethylsilyl β-cyclodextrin (TMS-βCD) or cucurbituril (CB7) with a bulky 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester (DF) as stoppers. These supramolecular compounds exhibited distinct improvement in the solubility, molecular weight, film forming ability, surface-morphological characteristics and reduced aggregation tendency compared to those of the neat compound. Also, the threading of conjugated backbones into macrocycles leads to an increasing environmental stability and resistance to quenching from impurities. Fluorescence emission (PL) shows vibronic transitions and a mono-exponential kinetics. The electrochemical data provided that the investigated compounds exhibited n- and p-doping processes. The encapsulation of DBT into TM-βCD or TMS-βCD cavities exhibits a greater effect on the LUMO, while the encapsulation into CB7 affects the HOMO energy levels. The HOMO/LUMO energy levels indicate that the investigated polyrotaxanes are electrochemically accessible as electron-transporting materials in electronic devices. Based on AFM analysis, polyrotaxane compounds exhibits a higher tendency to organize into fibers or linear ribbons.
Optical, electrochemical and surface-morphological properties of three terpolymer polyrotaxanes (1a, 1b and 1c) composed of 2,7-dibromo-9,9-dicyanomethylenefluorene encapsulated into γ-cyclodextrin (γCD), β- or γ-persilylated cyclodextrin (PS-γCD, PS-γCD) cavities (acceptor) and 4,4′-dibromo-4′′-methyltriphenylamine (donor) randomly distributed into 9,9-dioctylfluorene conjugated chains have been evaluated and compared to those of the reference 1. The role of the encapsulation on the thermal stability, solubility, film forming ability and transparency was also investigated. High fluorescence efficiency, almost identical normalized absorbance maximum in solution and solid-states of 1a, 1b and 1c provides the lower aggregation tendency. The fluorescence lifetimes (τ) of 1a, 1b and 1c follow a mono-exponential decay with a value τ = 1.11, 1.03 and 1.14 ns, compared with the neat 1, where a bi-exponential decay was identified. AFM studies reveal a smooth and homogenous surface morphology for polyrotaxanes than that of the reference. The electrochemical data provided that the investigated compounds exhibited n- and p-doping processes. The HOMO/LUMO energy levels 1a, 1b, 1c and 1 and in combination with the work function of anodic ITO glass substrates coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (-5.2 eV) and cathodic Ca (-2.8 eV) or Al (-2.2 eV) indicate that the compounds are electrochemically accessible as electron-transporting materials.
The photophysical properties of two polyazomethine polyrotaxanes (4•αCD and 4•TMS-αCD) composed of pyrene and triazole encapsulated into native and permodified α-cyclodextrin (αCD and TMS-αCD) cavities have been investigated and compared with those of the non-rotaxane 4 counterparts. Rotaxane formation results in improvements of the solubility in organic solvents, as well as better film forming ability combined with a high transparency. The polyrotaxane 4•TMS-αCD was soluble in toluene/DMF1/1 v/v mixture and displayed useful levels of thermal stability. The fluorescence spectroscopy of 4•αCD and 4•TMS-αCD shows an obvious blue shift both in excitation and emission spectra with respect to those of non-rotaxane counterparts. 4•TMS-αCD displays a continuous absorption spectrum, whereas the reference 4 does not show any absorption maximum, neither for its emission maximum, presumably because of its very low solubility in DMF. The improved fluorescence efficiency (ΦPL) of both polyrotaxanes is attributed to the hydrophobic micro-environment within αCD and TMS-αCD cavities. The surfaces of non-rotaxane 4 counterparts showed globular formations with an agglomeration tendency, while the encapsulated 4•αCD and 4•TMS-αCD rotaxane compounds exhibited smoother surfaces, comprised by smaller grains uniformly distributed on the surface of the solid films. The presence of the αCD and TMS-αCD in 4·αCD and 4•TMS-αCD polyrotaxanes affects the LUMO energy levels to a greater extent than its HOMO energy with respect to reference 4. The wetting properties of spin-coated film of 4•TMS-αCD in water (polar) and diiodomethane (apolar), indicates that TMS-αCD makes its surface more hydrophobic. The dispersive and polar components are lower than that of the reference compounds. The doping of the rotaxane structures with iodine (I2) indicated smaller improvements of electrical conductivity (σ) values, which presents a tradeoff with their better solubility, process ability, surface characteristics and ΦPL.