Water soluble pentacene

Abstract

A water soluble pentacene, potassium 3,3′-(pentacene-6,13-diylbis(sulfanediyl))dipropanoate (4), has been synthesized and characterized. The synthesis of 4 is straightforward and scalable, and its isolation does not require time consuming chromatographic separations. UV-vis spectra in several solvents indicate an optical HOMO–LUMO gap of approximately 1.91–1.97 eV. Water soluble pentacene 4 is long-lived in the solution phase and in the solid state. Because it forms stable solutions, inks based on 4 have been formulated and printed onto paper and flexible plastic using an unmodified commercial ink-jet printer. A bi-layer photovoltaic cell using 4 as donor and [60]fullerene as acceptor was fabricated and shown to be active. The crystal structure of the pentacene diacid precursor to water soluble pentacene 4 has been solved and shows a parallel displaced arrangement of pentacene rings, indicative of stabilizing π–π stacking interactions. DFT modeling for 4, however, suggests an unusual, low energy conformation in which both potassium carboxylate moieties are located on the same face (syn) of the pentacene π system. Likewise, calculated two-molecule stacks of 4 suggest a crystal packing arrangement in which potassium carboxylate moieties are intercalated between adjacent pentacene rings.