2 research outputs found
Electronic Delocalization in the Radical Cations of Porphyrin Oligomer Molecular Wires
The
radical cations of a family of Ļ-conjugated porphyrin arrays
have been investigated: linear chains of <i>N</i> = 1ā6
porphyrins, a 6-porphyrin nanoring and a 12-porphyrin nanotube. The
radical cations were generated in solution by chemical and electrochemical
oxidation, and probed by visāNIRāIR and EPR spectroscopies.
The cations exhibit strong NIR bands at ā¼1000 nm and 2000ā5000
nm, which shift to longer wavelength with increasing oligomer length.
Analysis of the NIR and IR spectra indicates that the polaron is delocalized
over 2ā3 porphyrin units in the linear oligomers. Some of the
IR vibrational bands are strongly intensified on oxidation, and Fano-type
antiresonances are observed when activated vibrations overlap with
electronic transitions. The solution-phase EPR spectra of the radical
cations have Gaussian lineshapes with linewidths proportional to <i>N</i><sup>ā0.5</sup>, demonstrating that at room temperature
the spin hops rapidly over the whole chain on the time scale of the
hyperfine coupling (ca. 100 ns). Direct measurement of the hyperfine
couplings through electronānuclear double resonance (ENDOR)
in frozen solution (80 K) indicates distribution of the spin over
2ā3 porphyrin units for all the oligomers, except the 12-porphyrin
nanotube, in which the spin is spread over about 4ā6 porphyrins.
These experimental studies of linear and cyclic cations give a consistent
picture, which is supported by DFT calculations and multiparabolic
modeling with a reorganization energy of 1400ā2000 cm<sup>ā1</sup> and coupling of 2000 cm<sup>ā1</sup> for charge transfer
between neighboring sites, placing the system in the RobināDay
class III
Electronic Delocalization in the Radical Cations of Porphyrin Oligomer Molecular Wires
The
radical cations of a family of Ļ-conjugated porphyrin arrays
have been investigated: linear chains of <i>N</i> = 1ā6
porphyrins, a 6-porphyrin nanoring and a 12-porphyrin nanotube. The
radical cations were generated in solution by chemical and electrochemical
oxidation, and probed by visāNIRāIR and EPR spectroscopies.
The cations exhibit strong NIR bands at ā¼1000 nm and 2000ā5000
nm, which shift to longer wavelength with increasing oligomer length.
Analysis of the NIR and IR spectra indicates that the polaron is delocalized
over 2ā3 porphyrin units in the linear oligomers. Some of the
IR vibrational bands are strongly intensified on oxidation, and Fano-type
antiresonances are observed when activated vibrations overlap with
electronic transitions. The solution-phase EPR spectra of the radical
cations have Gaussian lineshapes with linewidths proportional to <i>N</i><sup>ā0.5</sup>, demonstrating that at room temperature
the spin hops rapidly over the whole chain on the time scale of the
hyperfine coupling (ca. 100 ns). Direct measurement of the hyperfine
couplings through electronānuclear double resonance (ENDOR)
in frozen solution (80 K) indicates distribution of the spin over
2ā3 porphyrin units for all the oligomers, except the 12-porphyrin
nanotube, in which the spin is spread over about 4ā6 porphyrins.
These experimental studies of linear and cyclic cations give a consistent
picture, which is supported by DFT calculations and multiparabolic
modeling with a reorganization energy of 1400ā2000 cm<sup>ā1</sup> and coupling of 2000 cm<sup>ā1</sup> for charge transfer
between neighboring sites, placing the system in the RobināDay
class III