One- and Two-Dimensional Electron Transfer Processes in Triarylamines with Multiple Redox Centers

Abstract

Intramolecular electron transfer (ET) processes have been studied extensively in inorganic binuclear transition metal complexes; [1] organic donor ± acceptor systems that are bridged by s frameworks have been investigated in order to mimic biological ET processes. [2] In contrast, much less is known about purely organic Robin/Day [3] class II compounds with bridging p-electron systems and the electron transfer processes involved: Nelsen et al.[4] studied a number of bis(hydrazine)phenylene radical cations and related species; Bonvoisin et al.[5] investigated m-phenylene-bridged triarylamine systems. These radical cations are characterized by intervalence charge-transfer (IV-CT) bands in the NIR spectra which are associated with a photoinduced intramolecular electron transfer between two redox centers. As the coupling of redox centers over p-conjugated bridges is of central interest for the design of new optoelectronic materials, [6] it was our aim to study basic intramolecular electron transfer processes in simple symmetrically substituted p systems. We chose p-bridged triarylamine derivatives since triarylamines in general are important hole carrier systems, which are widely used in organic optoelectronic devices. [7] 4,4'-Bis(N,N-di-p-methoxyphenylamino)tolane (2) was synthesized by two Hagihara cross-coupling steps, and the corresponding trimer hexakis[4-(N,N-di-p-methoxyphenylamino)phenyl]benzene (3) was formed from 2 by catalysis with [Co 2 (CO) 8 ] (Scheme 1).[8] These derivatives should exhibit an intramolecular degenerate electron transfer in the singly and triply oxidized forms, respectively. Both neutral compounds are yellow, and their UV/Vis spectra in CH 2 Cl 2 contain a strong absorption band at 373 nm (2) and 308 nm (3, with a shoulder at 330 nm). The cyclic voltammogram (CV) [9] of 2 shows two waves at 200 and 340 mV (versus Fc/Fc ) in CH 2 Cl 2 (Figure 1) referring to two reversible oxidations. This corresponds to a comproportionation constant (K co 10 (DE/0.059) , where DE is the difference of redox potentials for the two oxidative steps) of 236 and suggests 2 to be a class II derivative. [1,3] In contrast, trimer 3 only shows one broad unresolved wave centered at 225 mV. This reversible oxidation process was calibrated by thin-layer coulometry with 2,5-bis(dicyanovinyl)furan as the reference, and it involves six electrons in total, leading to 3 6 . UV/Vis/NIR spectroelectrochemical investigation [10] of 2 shows that besides a band at 734 nm, which is characteristic for triarylamine radical cations, [11] a second very intense band 10 mm ethylenediamine tetraacetate (EDTA), 1 mm 1,4-dithiothreitol (DTT), and 1 % bovine serum albumen (BSA) at 4 8C in a volume of 400 mL. After 30 minutes this exchange reaction was stopped by the addition of MgCl 2 to give a final concentration of 25 mm and the enzyme´substrate (E´S) complex purified on a PD10 column. The purified E´S complex was divided into separate aliquots of 150 mL, and rGTP was added to give a final concentration of 50 mm. The reactions were...

Light-Induced Charge Separation in Densely Packed Donor–Acceptor Coordination Cages

“…One energy conversion strategy is based on the photoinduced generation of long-lived charge separation states. Therefore, several potent donor–acceptor ensembles varying from triarylamines or oligothiophenes to porphyrine derivatives combined with electron poor aromatic systems or carbon nanomaterials have been employed. On the other hand, dye-sensitized solar cells based on direct interfacial electron injection from excited chromophores, often ruthenium complexes, have reached impressive performance .…”

Synthesis and redox properties of mono-, di- and tri-metallic platinum-ethynyl complexes based on the trans-Pt(C6H4N{C6H4OCH3-4}2)(C CR)(PPh3)2 motif

“…Syntheses The key triarylamine building blocks 1 [47] and 2 [48,49] were assembled using the sequence of Ullmann and iodination reactions as illustrated in Scheme 1.…”

Iron-Catalyzed Synthesis, Structure, and Photophysical Properties of Tetraarylnaphthidines

“…The 1 H-NMR spectrum in combination with the HSQC (Figure 6) and the JRES spectra displayed signals for four substantially downfield-shifted doublets. On the basis of the fjord region effect observed for compound 4, these four downfield-shifted signals in the 1…”

“…The 1 H-NMR spectrum in combination with the HSQC (Figure 6) and the JRES spectra displayed signals for four substantially downfield-shifted doublets. On the basis of the fjord region effect observed for compound 4, these four downfield-shifted signals in the 1 The connectivity in compound 5 has been secured by a full set of 2D-NMR spectra (see below and the copies of the 2D-NMR spectra in the Supplementary Materials). The NMR spectra of 5 display signals for a non-symmetrical aromatic compound.…”

“…Triarylamines have been the subject of numerous studies due to their electron-rich character and the resulting low oxidation potentials [1][2][3]. These unique properties of triarylamine derivatives have induced extensive investigations towards their potential applications in organic films for optoelectronics [4] and as hole-transport materials in OLEDs (organic light emitting diodes) and solar cells [5][6][7][8].…”