Ultrathin films of poly[N-(2-cyanoethyl)pyrrole] and poly(N-methylpyrrole) and their composites with Au nanoparticles were used for the electrochemical detection of small concentrations (10 mM-100 μM) of dopamine, a neurotransmitter related with neurological disorders. Results indicated that Au nanoparticles improve the sensing abilities of the two polymers, even though they are not essential to obtain effective and fast responses toward the presence of dopamine. Furthermore, although both polymers have been found to be highly sensitive to low concentrations of dopamine, the response of poly[N-(2-cyanoethyl)pyrrole] is better and more effective than the response of poly(N-methylpyrrole). Experimental results were corroborated with quantum mechanical calculations on model systems, which also indicated that the interaction of oxidized dopamine with poly[N-(2-cyanoethyl)pyrrole] is stronger than that with poly(N-methylpyrrole). This behavior has been attributed to two different factors: (i) the flexibility of the cyanoethyl groups, which allows maximize the number of attractive van der Waals interactions, and (ii) the dipole of the cyano group, which interacts favorably with the dipole of the CO bonds of oxidized dopamine. Finally, theoretical results were used to propose an atomistic model that explains the interaction behavior between the oxidized dopamine and the conducting polymers.

In an attempt to relate atomistic information to the rheological response of a large dendritic object, interand intramolecular hydrogen bonds and p,p-interactions have been characterized in a dendronized polymer (DP) that consists of a polymethylmethacrylate backbone with tree-like branches of generation four (PG4) and contains both amide and aromatic groups. Extensive atomistic molecular dynamics simulations have been carried out on (i) an isolated PG4 chain and (ii) ten dimers formed by two PG4 chains associated with different degrees of interpenetration. Results indicate that the amount of nitrogen atoms involved in hydrogen bonding is ~11% while ~15% of aromatic groups participate in p,pinteractions. Furthermore, in both cases intramolecular interactions clearly dominate over intermolecular ones, while exhibiting markedly different behaviors. Specifically, the amount of intramolecular hydrogen bonds increases when the interpenetration of the two chains decreases, whereas intramolecular p,pinteractions remain practically insensitive to the amount of interpenetration. In contrast, the strength of the corresponding two types of intermolecular interactions decreases with interpenetration. Although the influence of complexation on the density and cross-sectional radius is relatively small, interpenetration affects significantly the molecular length of the DP. These results support the idea of treating DPs as long colloidal molecules.

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Density functional and time-dependent density functional calculations using the B3LYP method combined with the 6-31G(d) and 6-311++G(d,p) basis sets are performed on symmetric and unsymmetric all-thiophene dendrimers containing up to 45 thiophene rings. Calculations consider both the neutral and the oxidized states of each dendrimer. The results are used to examine the molecular geometry, the ionization potential, the lowest π-π* transition energy, and the shape of the frontier orbitals. The molecular and electronic properties of these systems depend not only on the number of thiophene rings, as typically occurs for linear oligothiophenes, but also on their symmetric/unsymmetric molecular architecture. Two mathematical models developed to predict the lowest π-π* transition energy of all-thiophene dendrimers that are inaccessible to quantum mechanical calculations are tested on a dendrimer with 90 thiophene rings.

The internal organization of macromonomers (MGs) consisting of all-thiophene dendrons of generation g= 2 and 3 attached to a phenyl core, as well as of the dendronized polymers resulting from polymerization of these macromonomers (PG2 and PG3, respectively), has been investigated using theoretical methods. The conformational preferences of the MGs, determined using density functional theory calculations, are characterized by the relative orientation between dendrons and core.We find that the strain of the MGs increases with the generation number and is alleviated by small conformational re-arrangements of the peripheral thiophene rings.The conformations obtained for the MGs have subsequently been used to construct models for the dendronized polymers. Classical molecular dynamics simulations have evidenced that the interpenetration of dendrons belonging to different repeat units is very small for PG2. In contrast, the degree of interpenetration is found to be very high for PG3, which also shows a significant degree of backfolding (i.e. occurrence of peripheral methyl groups approaching the backbone). Consequently, PG2 behaves as a conventional linear flexible polymer bearing bulk pendant groups, whereas PG3 is better characterized as a semirigid homogenous cylinder. The two polymers are stabilized by - stacking interactions, even though these are significantly more abundant for PG3 than for PG2; the average number of interactions per repeat unit is 3.0 and 8.8 for PG2 and PG3, respectively. While in these interactions the thiophene rings can adopt either parallel (sandwich) or perpendicular (T-shaped) dispositions, the former scenario turns out to be the most abundant.3