Pentacene to Octacene: The Limit of Fourfold TIPS-Ethynylation

Abstract

Soluble acenes beyond hexacene are rare. Their sensitivity complicates isolation, purification and application in devices. To increase the stability of acenes, functionalization with trialkylsilylethynyl substituents prevents [4+4] dimerization and oxidation. At the same time such acenes are soluble and processible. Here we present the modular synthesis of fourfold TIPS-ethynylated pentacenes to octacenes and investigate their optical and redox properties, frontier orbital positions (CV, DFT calculations) as well as their stability in solution (UV/vis, NMR spectroscopy). We also investigated their magnetic properties as a function of acene length. Pentacene, hexacene and heptacene are sufficiently stable to serve as semiconductors in thin-film transistors - the octacene rapidly decays to its butterfly dimer evidence by time-dependent NMR spectroscopy and crystal structure analysis.