The synthesis and properties of solution processable phenyl cored thiophene dendrimers

In this paper we describe the convergent synthesis of a new class of phenyl cored thiophene dendrimers, which are promising candidates for use in organic semiconductor devices. We have prepared dendrimers with three and four dendrons around the core as well as dendrimers with 1st and 2nd generation dendrons. All the dendrimers were soluble in common organic solvents such as chloroform, THF and toluene. The structures and size properties are confirmed by a number of techniques including NMR, GPC and MALDI-TOF-MS. Decomposition was studied by TGA with initial breakdown of the hexyl surface groups followed by the aromatic core. The spectroscopic properties were studied by UV-vis and PL spectrometry which demonstrated substantial differences between the dendrimers with three and four dendrons. Optical band gaps varied between 2.34 and 2.60 eV for thin films of the dendrimers and electronic band gaps were, on average, 0.3 eV greater than the optical band gaps. The smallest band gap was measured for the dendrimer with four 2nd generation dendrons around the phenyl core. Fluorescence lifetimes of the molecules in solution ranged from 200 to 560 ps. This range in values was attributed to differences in internal conversion rates associated with varying degrees of flexibility of the extended dendrons.