EPR and ENDOR Studies of Dimeric Paracyclophane Radical Cations and Dications Containing Tri- and Pentamethylene-Bridged p-Phenylene Diamine Units

Abstract

Solution EPR and ENDOR studies on the radical cations of three dimeric p-phenylene diamine (PD)-based compounds, the tetraisopropyl-substituted bis-trimethylene-bridged [5,5]paracyclophane 1(iPr)(+) and its tetramethyl- and tetraisopropyl-substituted bis-pentamethylene-bridged [7,7]paracyclophane analogues 3(Me)(+) and 3(iPr)(+), showed that charge is localized on one PD(+) unit on the EPR time scale in all three compounds and determined the nitrogen splitting constants and several of the hydrogen splitting constants for these complex spectra. Rigid glass studies of the diradical dications of 1(iPr)(2+), 3(iPr)(2+), and its tetramethylene-bridged [6,6]paracyclophane analogue 2(iPr)(2+), all of which show significant amounts of thermally excited triplet at low temperature, demonstrated that 1(iPr)(2+) has a singlet ground state but the triplet lies only 0.07 kcal/mol higher in energy, and 3(iPr)(2+) has its triplet lying 0.05 kcal/mol higher in energy than its singlet.

Oxidation Products of Doubly Trimethylene-Bridged Tetrabenzyl p-Phenylenediamine Paracyclophane

“…The singly Together with previous studies, [26][27][28][29]38 this work shows that molecular interactions of the organic radical ions are clearly sensitive to the solvent and counterion environment, which is also shown by theoretical studies on the spontaneous dimerization of TMPD radical cations. 39 We expect that deeper understanding from the molecular prospective of the intermolecular binding nature of the open-shell organic radicals can provide the basis for future discoveries of novel organic materials.…”

Intramolecular π‐Stacking Interactions of Bridged Bis‐p‐Phenylenediamine Radical Cations and Diradical Dications: Charge‐Transfer versus Spin‐Coupling

“…The EPR and ENDOR spectra of similar molecules with three and five carbon bridges have been published in collaboration with Gescheidt (T.U. Graz), and J values obtained from low temperature EPR intensity changes in collaboration with Teki (Osaka City University) 9…”

Photoswitchable mixed valence

“…This approach yields HAB 40 = 5550 cm -1 , a value close to those obtained for four chemically related bis(triarylamine) mixed valence systems with nonphotoswitchable bithiophene bridges and comparable N-N distances. 59 No IVCT bands can be observed for the open forms 12o + and 13o + . 45 The conclusion from this work on bis(triarylamine) systems is that photoisomerization of the DTE linker from the open to the closed form induces a changeover from class I mixed valence behavior to class II in the case of 13c + and to class III in the case of 12c + .…”

“…This approach yields H AB = 5550 cm À1 , a value close to those obtained for four chemically related bis(triarylamine) mixed valence systems with non-photoswitchable bithiophene bridges and comparable N-N distances. 59 No IVCT bands can be observed for the open forms 12o + and 13o + .…”