title: On the Importance of Electronic Symmetry for Triplet State Delocalization.
abstract: The influence of electronic symmetry on triplet state delocalization in linear zinc porphyrin oligomers is explored by electron paramagnetic resonance techniques. Using a combination of transient continuous wave and pulse electron nuclear double resonance spectroscopies, it is demonstrated experimentally that complete triplet state delocalization requires the chemical equivalence of all porphyrin units. These results are supported by density functional theory calculations, showing uneven delocalization in a porphyrin dimer in which a terminal ethynyl group renders the two porphyrin units inequivalent. When the conjugation length of the molecule is further increased upon addition of a second terminal ethynyl group that restores the symmetry of the system, the triplet state is again found to be completely delocalized. The observations suggest that electronic symmetry is of greater importance for triplet state delocalization than other frequently invoked factors such as conformational rigidity or fundamental length-scale limitations.
authors.affiliation: Centre for Advanced Electron Spin Resonance (CAESR), University of Oxford , South Parks Road, Oxford OX1 3QR, United Kingdom.
authors.forename: Sabine
authors.identifier: 0000-0002-2990-974X
authors.initials: S
authors.lastname: Richert
authors.affiliation: Department of Chemistry, Duke University , French Family Science Center, 124 Science Drive, Durham, North Carolina 27708, United States.
authors.forename: George
authors.initials: G
authors.lastname: Bullard
authors.affiliation: Department of Chemistry, Duke University , French Family Science Center, 124 Science Drive, Durham, North Carolina 27708, United States.
authors.forename: Jeff
authors.identifier: 0000-0002-8431-0772
authors.initials: J
authors.lastname: Rawson
authors.affiliation: Department of Physics, Saint Joseph's University , 5600 City Avenue, Philadelphia, Pennsylvania 19131, United States.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Angiolillo
authors.affiliation: Department of Chemistry, Duke University , French Family Science Center, 124 Science Drive, Durham, North Carolina 27708, United States.
authors.forename: Michael J
authors.identifier: 0000-0003-4876-0036
authors.initials: MJ
authors.lastname: Therien
authors.affiliation: Centre for Advanced Electron Spin Resonance (CAESR), University of Oxford , South Parks Road, Oxford OX1 3QR, United Kingdom.
authors.forename: Christiane R
authors.identifier: 0000-0003-1828-7700
authors.initials: CR
authors.lastname: Timmel