Blending through-space and through-bond π-π-coupling in [2,2']-paracyclophane-oligophenylenevinylene molecular wires

J Am Chem Soc. 2013 Jul 17;135(28):10372-81. doi: 10.1021/ja401239r. Epub 2013 Jul 3.

Abstract

A series of ZnP-pCp-oPPV-C60 conjugates covalently connected through [2,2']-paracyclophane-oligophenylenevinylene (pCp-oPPV) bridges containing one, two, and three [2,2']-paracyclophanes (pCps) has been prepared in multistep synthetic procedures involving Horner-Wadsworth-Emmons olefination reactions and/or Heck type Pd-catalyzed reactions. Molecular modeling suggests that charge transfer is effectively mediated by the pCp-oPPVs through a predominant hole-transfer mechanism. Photophysical investigation supports molecular modeling and reveals two major trends. On one hand, C60 excitation of 1, 2, and 3 leads exclusively to charge transfer between pCp and C60 to afford a ZnP-(pCp-oPPV)(•+)-C60(•-) radical ion pair state without giving rise to a subsequent charge shift to yield the ZnP(•+)-pCp-oPPV-C60(•-) radical ion pair state. On the other hand, ZnP excitation of 1, 2, and 3 results in a rather slow charge transfer between ZnP and C60, after which the ZnP(•+)-pCp-oPPV-C60(•-) radical ion pair state evolves. In temperature-dependent ZnP fluorescence experiments, which were performed in the temperature range from 273 to 338 K, two domains are discernible: low and high temperature behaviors. In the low temperature range (i.e., below 30 °C) the rate constants do not change, suggesting that a superexchange mechanism is the modus operandi. In the high temperature range (i.e., >30 °C) the rate constants increase. Moreover, we find rather strong distance dependence for 1 and 2 and weak distance dependence for 2 and 3. A damping factor of 0.145 Å(-1) is derived for the former pair and 0.012 Å(-1) for the latter.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Fullerenes / chemistry*
  • Models, Molecular
  • Molecular Structure
  • Organometallic Compounds / chemical synthesis
  • Organometallic Compounds / chemistry*
  • Polycyclic Compounds / chemistry*
  • Polyvinyls / chemistry*
  • Quantum Theory
  • Zinc / chemistry*

Substances

  • Fullerenes
  • Organometallic Compounds
  • Polycyclic Compounds
  • Polyvinyls
  • poly(4-phenylenevinylene)
  • (2.2)paracyclophane
  • Zinc
  • fullerene C60