p‐Phenyleneethynylene Molecular Wires: Influence of Structure on Photoinduced Electron‐Transfer Properties

Abstract

A series of donor-acceptor arrays (exTTF-oPPE-C60) containing pi-conjugated oligo(phenyleneethynylene) wires (oPPE) of different length between pi-extended tetrathiafulvalene (exTTF) as electron donor and fullerene (C60) as electron acceptor has been prepared by following a convergent synthesis. The key reaction in these approaches is the bromo-iodo selectivity of the Hagihara-Sonogashira reaction and the deprotecting of acetylenes with different silyl groups to afford the corresponding donor-acceptor conjugates in moderate yields. The electronic interactions between the three electroactive species were determined by using UV-visible spectroscopy and cyclic voltammetry. Our studies clearly confirm that, although the C60 units are connected to the exTTF donor through pi-conjugated oPPE frameworks, no significant electronic interactions are observed in the ground state. Theoretical calculations predict how a simple exchange from C=C double bonds (i.e., oligo(p-phenylenevinylene) to C triple chemical bond C triple bonds (i.e., oPPE) in the electron donor-acceptor conjugates considerably alters long-range electron transfer. Photoexcitation of exTTF-oPPE-C60 leads to the following features: a transient photoproduct with maxima at 660 and 1000 nm, which are unambiguously attributed to the photolytically generated radical-ion-pair state, [exTTF*+-oPPE-C60*]. Both charge-separation and charge-recombination processes give rise to a molecular-wire behaviour of the oPPE moiety with an attenuation factor (beta) of (0.2+/-0.05) A(-1).

Oligo(p‐phenyleneethynylene) (OPE) Molecular Wires: Synthesis and Length Dependence of Photoinduced Charge Transfer in OPEs with Triarylamine and Diaryloxadiazole End Groups

“…[18] UV-Visible absorption studies on OPE wires terminated with dialkylamino donor and cyano, formyl or nitro acceptor groups showed a competition between the extension of the chromophores and a decrease of the ICT upon increasing the number of PE repeat units. [19] More extensive photophysical studies on series of extended-TTF-OPE-pyrrolidinoC 60 , [20,21] porphyrin-OPE-pyrrolidinoC 60 [22] and 3,5-dimethyl-4-(9-anthracenyl)julolidine-OPEnaphthalene-bis(dicarboximide) systems [23] gave  values of 0.20, 0.11 and 0.23 Å -1 , respectively. Other examples include boron dipyrromethene (BODIPY)-OPE systems.…”

“…[21,23,38] The experimental data can be readily fitted to equation 1 giving an attenuation factor of = 0. [22] and = 0.20 Å -1 for extended-TTF-OPE-pyrrolidinoC 60 .…”

“…[22] and = 0.20 Å -1 for extended-TTF-OPE-pyrrolidinoC 60 . [20,21] These relatively large values for OPE bridges indicate that the length of the bridge has a significant impact on the ICT process. For comparison, oligo-p-phenylenevinylene (OPV) bridges, albeit with different D and A moieties, can give much lower values, indicative of more effective conjugation, e.g.…”

Light‐Harvesting Materials for Organic Electronics

“…The higher values of the attenuation factor revealed that the HOMO for this system is completely localized on the exTTF and does not reach into the bridge. The presence of triple bonds in exTTF-oPPE-C 60 disrupts the extended π-conjugation and influences in the charge transfer [79].…”

Fullerene-Indole-Nitrobenzene Hybrid System Connected Through Pyrazoline Ring: Synthesis, Electrochemical, and Photophysical Studies

“…During the past few years, electron donor-acceptor (DA) dyads based on [60] fullerene, which upon photoexcitation give rise to photoinduced charge-separated states, have been the focus of intensive research as candidates for artificial photosynthetic reaction centers (5)(6)(7)(8)(9)(10). Remarkably, small reorganization energies (11) associated with the reduction of the C 60 cage lead to efficient photoinduced electron transfer occurring, with the generation of relatively long-lived charge-separated (CS) states.…”