Synthesis and Optoelectronic Properties of Nanometer‐Sized and Highly Soluble Homocoupled Oligodiacetylenes

Abstract

Abstract Color and shape of oligodiacetylenes : We synthesized a series of highly soluble homocoupled oligodiacetylenes (HODAs). The color of these oligomers is dependent on the molecular length and aggregation state (see picture). The optical properties of these materials were studied by using both steady‐state and time‐resolved spectroscopic techniques. magnified image A new series of pure, nanometer‐sized and highly‐soluble homocoupled 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 λ max and the ε max of absorption for these HODAs show an increase with the chain elongation. The λ 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 λ 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).