title: 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.
authors.affiliation: Institute of Physical and Theoretical Chemistry, Graz University of Technology, Technikerstrasse 4/I, A-8010 Graz.
authors.forename: Arnulf
authors.initials: A
authors.lastname: Rosspeintner
authors.forename: Markus
authors.initials: M
authors.lastname: Griesser
authors.forename: Isao
authors.initials: I
authors.lastname: Matsumoto
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Teki
authors.forename: Gaoquan
authors.initials: G
authors.lastname: Li
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Nelsen
authors.forename: Georg
authors.initials: G
authors.lastname: Gescheidt