Abstract
A new series of pure, nanometer-sized and highly-soluble homo-coupled oligodiacetylenes (HODA) consisting of two symmetrical oligodiacetylene units was synthesized with high yield and on a multi-milligram scale under mild, catalytic Sonogashira conditions. The lambda(max) and the epsilon(max) of absorption for these HODAs show an increase with the chain elongation. The lambda(max) converges to 450 nm for the longest members of the series at micromolar concentration and to 462 nm for thin drop-casted films. An additional red-shifted absorption is observed in the solid state and in solution at low temperatures, which is caused by aggregation. The lambda(max) of the fluorescence emission increases with the chain length and reaches 492 nm for the longest oligomer. The fluorescence quantum yield has its maximum for the shortest oligomer and decreases rapidly for the longer ones. A similar trend is found for the fluorescence lifetime with a maximum of 100 ps for the homocoupled monomer. The rotational correlation time shows a linear increase with the oligomer length. This reveals a significant persistence length and indicates that the HODA molecules are fully stretched molecular rods (up to 8.2 nm).