Comparison of Alternant and Nonalternant Aromatic Bridge Systems with Respect to Their ET-Properties

Abstract

The bis(triarylamine) systems 1−5 were synthesized and investigated by spectroscopic and electrochemical methods. They all have an aromatic five-membered ring system in common as a central part of their π-electron bridge. The absorption spectra are presented. All compounds undergo five oxidations whereupon only the first two are reversible under semi-infinite cyclic voltammetry conditions. The spectra of the radical cations and dications of 1−5 were collected upon stepwise titration with SbCl5. All monoradical cations exhibit rather intense absorption bands in the NIR region that are assigned to optically induced charge transfer between the amine redox centers or between the amine redox center and aromatic bridge. It is suggested that with CH2Cl2 as solvent the charge in 1 + and 2 + is localized mainly at the peripheral amine redox centers whereas 3 + and 4 + are symmetrically delocalized systems with the highest charge density at the bridge. Upon increasing the solvent polarity, solvent induced symmetry breaking occurs as previously reported for the anthracene derivative 7 + . Less clear is the situation in 5 + . The nonalternant azulene derivative 4 behaves entirely different with respect to its optical and electrochemical properties if compared with the alternant naphthalene compound 6. The 1,3-azulene bridging unit turns out to mediate a strong electronic coupling combined with a low-oxidation potential.

Two Structural and Functional Domains of MESD Required for Proper Folding and Trafficking of LRP5/6

“…For residue H46, we notice that it is in close proximity to the conserved H207 of the BP domain (Figure 3C). The planar aromatic side chains of these two histidine residues stack closely against each other, forming a potential aromatic bridge or πelectron stacking (Noll et al, 2007). K183 of the BP domain may also play a role to stabilize this interaction.…”

Charge Delocalization in a Homologous Series of α,α′-Bis(dianisylamino)-Substituted Thiophene Monocations

“…15 Indeed, the oneelectron oxidized or one-electron reduced forms of several oligo-p-phenylene and oligo-p-phenylene vinylene systems could be described well as organic mixed-valence compounds in various experimental studies, [16][17][18][19][20][21][22][23][24][25] but until now there has been comparatively little conceptually analogous work on thiophene systems. [26][27][28][29][30][31][32][33][34][35] A notable exception is the recent study of the oxidized forms of bis (4-(alkoxyphenyl)amino) derivatives of dithienylethene and bithiophene and the finding that a mixed-3 valence description of these cations is meaningful. 36 Another exception is our own recent investigation of photoswitchable organic mixed-valence in dithienylethene systems.…”

Redox-State Dependent Spectroscopic Properties of Porous Organic Polymers Containing Furan, Thiophene, and Selenophene

“…[14] The cyclic voltammograms for POP-S and POP-Se are similar to that of POP-O with one broad oxidation peak at ,0.5 V versus Fc/Fc þ ( Fig. S2b,c; Supplementary Material), assigned to oxidation of the triarylamine core to its radical cation state in addition to oxidation of the thiophene or selenophene rings.…”

“…The band at ,20000 cm À1 is attributed to a charge transfer interaction from the triarylamine core to the furan bridge and is consistent with previous reports for monomeric systems. [14] The broad overlapping bands at . 22500 cm À1 are assigned to the localised aromatic p -p* transitions of the triarylamine core and furan linker.…”

“…The efficiency of triarylamines as hole conductors in organic polymers and films has been previously demonstrated where the degree of electron transfer is able to be tuned by variation of the linker between triarylamine cores. [9,10,[12][13][14] Heterocycles such as thiophenes have been demonstrated to provide efficient electron transfer between 'holes' in a system, with high charge carrier mobility in addition to good thermal and photo stabilities. [15,16] Systematic variation in the heterocycle used, from furan through to thiophene and selenophene, is hypothesised to result in increasingly electronically delocalised materials by virtue of the more diffuse orbitals of the heteroatoms further down the periodic table.…”