Photophysical and Electrochemical Properties of Push–Pull Oligo(ferrocenyl-phenyleneethynylene)s: Supramolecular Orders in Molecular Films

Abstract

We report on the optoelectronic properties of a series of unsymmetrical π-conjugated phenyleneethynylene macromolecules bearing ferrocene (Fc) as the electron-donor group (D), (benzyl) benzoate (Bz) or benzoic acid (Ac) as the electron attractor group (A) and connected through 2,5-di(alcoxy) phenyleneethynylene(s) (nPE) with n = 1, 2, 3 as π-conjugated bridges. In the series, by increasing the distance between the electron-attracting and electron-donor groups, the push−pull effect decreases. The intramolecular charge transfer (D → π → A) was evaluated by static and dynamic spectroscopy, electrochemistry, and density functional theory (DFT) theoretical calculations. The longest oligomer Fc3PEBz formed the best optical quality films. A study at the atomic level by scanning tunneling microscopy (STM) revealed that the molecules self-assemble on highly ordered pyrolytic graphite (HOPG) in domains with a short-range order. Films are mesoporous and the molecules arrange in a lamellar-like pattern, with an edge-on conformation with respect to HOPG, where the conjugated backbones lie parallel to the surface. Two different assemblies were identified in the monoatomic film, which depends on the ferrocene−ferrocene or benzyl−benzyl interactions.

Diruthenium Complexes with π-Extended Bridging Bis(alkenyl)arylene Ligands, A Derived Metallamacrocycle, and Their Oxidized Forms

“…OPVs and OPEs are paradigmatic examples of oligomers that become electrically conductive upon doping with a suitable oxidant or reductant and are hence dubbed “synthetic metals”. , Their (semi)conducting properties upon doping, , their wirelike behavior in single-molecule nanoelectrode setups, , their chemical stability, and their interesting optical and luminescence properties, − including electroluminescence, are attractive assets. The stiffer rigid-rod structures of ethynylene-bridged poly(phenyleneethynylenes) (PPEs) are often thought to decrease the impact of ring torsions along the π-conjugated backbone. − The ability of molecule-based wires with varying numbers of identical π-conjugated repeat units in their backbones to transport charge over longer distances can be evaluated by measuring the decay of conductance G as a function of the molecular length L . The latter scales according to G = A · e − β L where β is the so-called attenuation factor. , For OPVs and OPEs, β values for charge transport according to the superexchange mechanism, i.e., through direct orbital interactions, are in the range of 0.14–0.18 ,,, and 0.20–0.34 Å –1 , ,− respectively.…”