The optical and redox properties of a series of 3,4‐ethylenedioxythiophene oligomers (EDOTn, n=1–4) and their β,β′‐unsubstituted analogues (Tn, n=1–4) are described. Both series are end capped with phenyl groups to prevent irreversible α‐coupling reactions during oxidative doping. Absorption and fluorescence spectra of both series reveal a significantly higher degree of intrachain conformational order in the EDOTn oligomers. Oxidation potentials (EPA1 and EPA2) determined by cyclic voltammetry reveal that those of EDOTn are significantly lower than the corresponding Tn oligomers as a consequence of the electron‐donating 3,4‐ethylenedioxy substitution. Linear fits of EPA1 and EPA2 versus the reciprocal number of double bonds reveal significantly steeper slopes for the EDOTn than for the Tn oligomers. This could indicate a more effective conjugation for the EDOTn series, confirmed by the fact that coalescence of EPA1 and EPA2 is reached already at relatively short chain lengths (≈5 EDOT units) in contrast to the Tn series (>10 thiophene units). The stepwise chemical oxidation of the EDOTn and Tn oligomers in solution was carried out to obtain radical cations and dications. The energies of the optical transitions of the radical cations and dications as determined by UV/Vis/NIR spectroscopy were similar for the two series. These spectroscopic observations are consistent with quantum‐chemical calculations performed on the singly charged molecules. Cooling solutions containing T2.+, T3.+, EDOT2.+, and EDOT3.+ revealed the reversible formation of dimers, albeit with a somewhat different tendency, expressed in the values for the dimerization enthalpy.

Self-complexation of triblock copolymers based on undeca-and heptadecathiophene cores attached to generation three Fre ´chet-type poly(benzyl ether) dendrons in solution at low temperature leads to the formation of relatively small but well-defined supramolecular assemblies. The formation of these aggregates is associated with a strong thermochromic effect. Upon cooling dilute solutions, minor concentration-independent changes in the optical absorption due to intrachain planarization precede significant concentration-dependent thermochromic changes that are shown to originate from intermolecular π-π stacking interactions. The structurally well-defined nature of the substrates enables the determination of distinct temperature regimes for both intra-and intermolecular thermochromic changes. Furthermore, combining thermodynamic expressions for both the concentration and temperature dependence of aggregation allows a quantitative analysis of the self-assembly phenomenon. The results show that the supramolecular aggregates are relatively small, yet well-defined involving from 5 to 6 molecules in an average aggregate. The apparent size limitation of the aggregates is ascribed to steric constraints imparted by the dendritic wedges. Relatively high exothermicities accompany the aggregation process, increasing with conjugation length from -73.0 kJ/mol with the undecathiophene triblock (G3-T11-G3) to -85.8 kJ/mol for the heptadecathiophene analogue (G3-T17-G3), suggesting that π-π stacking is the driving force for complexation.

Favorable alignment of regio‐irregular poly(3‐alkylthiophene)s in a film can be attained, despite the fact that these polymers lack an intrinsic tendency to form well‐ordered supramolecular aggregates. As reported here, alignment can be achieved simply by oxidizing the polymer in solution prior to film formation. A delicate balance between the degree of order and the level of oxidation in solution is observed. These results point to a way to improve charge transport efficiency, which is influenced by intra‐ and interchain order in the polymer.

Photoluminescence (PL) and photoinduced absorption (PIA) spectroscopy measurements were performed on two lengthy oligothiophenes, G3-T11-G3 and G3-T17-G3, doubly end-substituted with third generation poly-benzyl ether dendrons. These oligothiophenes form well-defined nanoaggregates in dichloromethane solution upon cooling. The molecularly dissolved and aggregated phases interconvert reversibly in a narrow temperature range. PL and PIA spectroscopy were used to investigate the optical signatures of photoexcited singlet, triplet, and charged states as a function of aggregation. The extent of aggregation could be controlled by varying the temperature. Both the fluorescence and the triplet absorption spectra of the aggregated phase were significantly bathochromically shifted when compared to the spectra of the isolated molecules in solution. These bathochromic shifts indicate that interchain delocalization of the singlet and triplet photoexcitations occurs within the dendritic nanoassemblies. Charged states of G3-T11-G3 and G3-T17-G3 were selectively created by photoexcitation in the presence of an external electron acceptor (tetracyanoethylene). The principal absorption bands of the charged states shift to lower energy upon aggregation. Surprisingly, new high-energy bands are observed in the PIA spectrum of the aggregated phase. These transitions are clear signatures of two-dimensionally delocalized polaronic charge carriers within the nanoaggregates (i.e. intermolecular delocalization over the constituent molecules within the aggregate).