Properties of oligothiophene dendrimers as a function of molecular architecture and generation number.

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.