Self‐Assembled Conjugated Thiophene‐Based Rotaxane Architectures: Structural, Computational, and Spectroscopic Insights into Molecular Aggregation

Abstract

A comparative study of the self‐assembly at a variety of surfaces of a dithiophene rotaxane 1⊂β‐CD and its corresponding dumbbell, 1, by means of atomic force microscopy (AFM) imaging and scanning tunneling microscopy (STM) imaging on the micrometer and nanometer scale, respectively. The dumbbell is found to have a greater propensity to form ordered supramolecular assemblies, as a result of π–π interactions between dithiophenes belonging to adjacent molecules, which are hindered in the rotaxane. The fine molecular structure determined by STM was compared to that obtained by molecular modelling. The optical properties of both rotaxane and dumbbell in the solid state were investigated by steady‐state and time‐resolved photoluminescence (PL) experiments on spin‐cast films and diluted solutions. The comparison between the optical features of the threaded and unthreaded systems reveals an effective role of encapsulation in reducing aggregation and exciton migration for the rotaxanes with respect to the dumbbells, thus leading to higher PL quantum efficiency and preserved single‐molecule photophysics for longer times after excitation in the threaded oligomers.

Synthesis and electro‐optical properties of polyfluorene modified with randomly distributed electron‐donor and rotaxane electron‐acceptor structural units in the main chain

“…1 × 10 −5 M solution) 38. As shown in Table 2, the ϕ PL of the synthesized PF copolymer is lower than that reported for a copolymer with PFO and electron‐donating TA moities,4 but similar with other reported results 22, 27, 29. However, we found that this shortcoming could be overcome by protecting the acceptor unit through its encapsulation into a macrocycle γCD molecule.…”

“…Besides this, one should also consider as reason for higher ϕ PL the relocation of acceptor molecule into the more hydrophobic environment, which restricts rotational and vibrational motions and decreases the nonradiative decay pathways 40, 41. The enhanced ϕ PL can also be explained by a more planar and rigid structure of PF•γCD copolymer, which sterically prevents close contact between the aromatic cores and preserves single‐molecule photophysics for longer times after excitation 23, 29, 42…”

“…The construction of mechanically interlocked molecules, such as rotaxanes and polyrotaxanes, was also investigated as a method of further improvement of electronic properties through insulating the backbones of conjugated polymers for controlling intermolecular interactions 22–31. These studies revealed an attractive approach to achieve higher degree of control over molecular rigidity, prevention of aggregation, fluorescence efficiency, improved solubility, and surface‐morphological properties of the resulting conjugated polyrotaxanes 24–31…”

Redox‐Active Peptide‐Functionalized Quinquethiophene‐Based Electrochromic π‐Gel

“…[51] Among the varietieso fs mall molecular and polymerico rganic electrochromic materialsu sedi ne lectrochromic devices, oligothiophenesa sw ella s polythiophene derivatives area ni mportant classo fp-conjugated organic material. [52][53][54][55][56] Thiophene-based oligomersa nd polymers possess intrinsicc ontrasting colours between the neutral ando xidized forms concomitantw ithf orming stable intermediates. [57][58][59][60] Moreover,polythiophenese xhibits everal additionaladvantagesi ncluding well definedm olecular backbone,s olution processability,p recise molecular ordering andc rystallinityf or superior charge transfer.T he molecular structurei sakeyf actorf or molecularp acking induced by severaln on-covalenti nteractions, whichi nfluence the morphology of materials.…”

Effect of permodified β-cyclodextrin on the photophysical properties of poly[2,7-(9,9-dioctylfluorene)-alt-(5,5′-bithiophene)] main chain polyrotaxanes

“…This possibility represents an attractive approach to achieve control over molecular rigidity, prevention of aggregation, improved PLQE, and surface‐morphological characteristics of the resulting conjugated polyrotaxanes. Macrocyclic encapsulation of conjugated monomers into native cyclodextrins (CDs), as macrocycle host molecules followed by polymerization has been employed as an alternative supramolecular approach to achieve an “insulation” of the individual molecular wires . Such threading of macrocycles onto the conjugated chains does not disrupt the π‐conjugation and can additionally improve the solubility as well as the morphological characteristics of the resulting polymers.…”