Interplay of orbital tuning and linker location in controlling electronic communication in porphyrin arrays

Sung Ik Yang, Jyoti Seth, Thiagarajan Balasubramanian, Dongho Kim, Jonathan S. Lindsey, Dewey Holten, David F. Bocian

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111 Citations (Scopus)

Abstract

The β-diphenylethyne-linked porphyrin dimers ZnFbU-β (nonlinking meso- mesityl substituents) and F30ZnFbU-β (nonlinking meso-pentafluorophenyl substituents) and their bis-Zn analogues have been examined by static spectroscopic (absorption, fluorescence, electron paramagnetic resonance), time-resolved spectroscopic (absorption, fluorescence), and electrochemical (cyclic and square-wave voltammetry, coulometry) methods. The β-linked dimers were examined to test the hypothesis that the nature of the porphyrin HOMO (a(1u) versus a(2u)) in concert with the position of the linker (β- pyrrole or meso carbon) mediates electronic communication (excited-state energy transfer, ground-state hole-hopping). The major findings are as follows: (7) The rate of energy transfer is (56 ps)-1 for ZnFbU-β and (24 ps)-1 for F30ZnFbU-β. (2) The rate of hole/electron hopping in the monooxidized bis-Zn complex [F30Zn2U-β]+ is in the fast-exchange limit and is at least comparable to that for [Zn2U-β]+. These findings indicate that the presence of pentafluorophenyl groups causes enhancement of electronic communication in the β-linked dimers but attenuation in the meso- linked dimers. These opposite effects in the β- versus meso-linked dimers are explained by the fact that both pentafluorophenyl-substituted dimers have a(1u) HOMOs, which exhibit significant β-pyrrole electron density, whereas both mesityl-substituted dimers have a(2u) HOMOs, which exhibit large meso- carbon density. Thus, the combination of an a(1u) HOMO with a β-linker or an a(2u) HOMO with a meso linker results in optimal electronic communication. Collectively, these results demonstrate that the nature of the frontier orbitals and position of connection of a covalent linker (in addition to distance, orientation, and energetics) must be considered in the design architecture of molecular photonic devices.

Original languageEnglish
Pages (from-to)4008-4018
Number of pages11
JournalJournal of the American Chemical Society
Volume121
Issue number16
DOIs
Publication statusPublished - 1999 Apr 28

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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