Monotrimethylene-bridged bis-p-phenylenediamine radical cations and dications: spin states, conformations, and dynamics.
J Phys Chem A
; 117(7): 1439-48, 2013 Feb 21.
Article
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| ID: mdl-23339358
ABSTRACT
The properties of p-phenylenediamine- (PD-) based systems substantially depend on the molecular topology. The singly bridged PD analogues HMPD and OMPD in which the PD rings are connected by a flexible linker reveal particular electronic properties in their radical cations and dications. The EPR and UV-vis spectra of HMPD(2+â¢â¢) were found to be exceptionally temperature-sensitive, following a change from the extended conformation (doublet-doublet state) predominant at room temperature to the π-stacked conformation (singlet state) prevailing at dry-ice temperature. Changing the single bridge from (CH(2))(3) to dimethylated CH(2)CMe(2)CH(2) in OMPD(2+â¢â¢) causes considerably less of the π-stacked conformation to be present at low temperature as a result of the steric interactions with the methyl groups of the bridge. In contrast to HMPD(2+â¢â¢) and OMPD(2+â¢â¢), in which the positive charges are localized separately in each PD(+â¢) ring, in the extended conformation, exchange of the electron ("hole hopping") between the two PD units (fast at the time scale of EPR experiments) was observed for HMPD(+â¢) and OMPD(+â¢). This process slows in a reversible manner with decreasing temperature, thus forming the radical cation with the unpaired electron spin density predominantly on one PD core, at low temperatures. Accordingly, a subtle balance between conformational changes, electron delocalization, and spin states could be established.
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Colección:
01-internacional
Base de datos:
MEDLINE
Idioma:
En
Revista:
J Phys Chem A
Asunto de la revista:
QUIMICA
Año:
2013
Tipo del documento:
Article
País de afiliación:
Austria