title: Tuning aryl, hydrazine radical cation electronic interactions using substituent effects.
abstract: Absorption spectra for 2,3-diaryl-2,3-diazabicyclo[2.2.2]octane radical cations (2(X)(*+)) and for their monoaryl analogues 2-tert-butyl-3-aryl-2,3-diazabicyclo[2.2.2]octane radical cations (1(X)(*+)) having para chloro, bromo, iodo, cyano, phenyl, and nitro substituents are reported and compared with those for the previously reported 1- and 2(H)(*+) and 1- and 2(OMe)(*+). The calculated geometries and optical absorption spectra for 2(Cl)(*+) demonstrate that p-C6H4Cl lies between p-C6H4OMe and C6H5 in its ability to stabilize the lowest energy optical transition of the radical cation, which involves electron donation from the aryl groups toward the pi*(NN)(+)-centered singly occupied molecular orbital of 2(X)(*+). Resonance Raman spectral determination of the reorganization energy for their lowest energy transitions (lambda(v)(sym)) increase in the same order, having values of 1420, 5300, and 6000 cm(-1) for X = H, Cl, and OMe, respectively. A neighboring orbital analysis using Koopmans-based calculations of relative orbital energies indicates that the diabatic aryl pi-centered molecular orbital that interacts with the dinitrogen pi system lies closest in energy to the bonding pi(NN)-centered orbital and has an electronic coupling with it of about 9200 +/- 600 cm(-1), which does not vary regularly with electron donating power of the X substituent.
authors.affiliation: Department of Chemistry and Biochemistry, University of California Los Angeles, California 90095, USA.
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Valverde-Aguilar
authors.forename: Xianghuai
authors.initials: X
authors.lastname: Wang
authors.forename: Edward
authors.initials: E
authors.lastname: Plummer
authors.forename: Jenny V
authors.initials: JV
authors.lastname: Lockard
authors.forename: Jeffrey I
authors.initials: JI
authors.lastname: Zink
authors.forename: Yun
authors.initials: Y
authors.lastname: Luo
authors.forename: Michael N
authors.initials: MN
authors.lastname: Weaver
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Nelsen