Inhibition of the Formation and Decay of Stilbene Core Radical Cations by the Dendron during the Photoinduced Electron Transfer

Abstract

Formation and decay processes of stilbene core radical cation (ST*+) during the photoinduced electron transfer have been studied for a series of stilbene bearing benzyl ether-type dendrons (D). ST*+ and the radical cation of peripheral dendron (D*+) were generated by intermolecular hole transfer from biphenyl radical cation, which was generated from photoinduced electron transfer from biphenyl to the singlet-excited 9,10-dicyanoanthracene in a mixture of acetonitrile and 1,2-dichloroethane (3:1). An intramolecular dimer radical cation of benzyl groups at the terminal of stilbene dendrimer was indicated as a hole trapping site. Subsequent hole transfer from the trapping site to the core ST generated ST*+. The shielding effects of D depending on the dendrimer generation on the growth and decay of ST*+ were observed. It was revealed for the first time that D acts as the hole trapping site and the hole conductor on the way of the exothermic hole transfer from the terminal of D to the central core ST. We also found that D inhibits the charge recombination with 9,10-dicyanoanthracene radical anion because of the steric hindrance.

Long-Lived Hole Stabilized at a Triphenylamine Core and Shielded by Rigid Phenylazomethine Dendrons: A Pulse Radiolysis Study

“…Higher generation of DPA might disturb further the complete conformational stabilization and delocalization of the positive charge at the core, which is supported by the abovementioned Mark−Houwink relationship. No significant dependence of the extinction coefficient on the generation number has been observed for the stilbene core with benzyl ether dendrons . On the contrary, we demonstrated for the first time a systematic decrease in the oscillator strength together with a red shift of the photoabsorption peak with an increase in the generation number of the dendrimers bearing rigid dendrons.…”

“…Enhancement of the charge transport efficiency is essential for applications to OLEDs and organic thin-film transistors. By inducing a positive charge at the dendrimer shell by photolysis, Hara and Majima et al have demonstrated hole transfer from benzyl ether dendrons to the stilbene core, suggesting an effective shielding of the core radical cation against chloride ions . Ghaddar et al have reported photoabsorption spectra of radical anions from a ruthenium core in a biphenyl dendron by pulse radiolysis and found a spectral shift and decrease in absorbance …”

Dihydrophenanthrene-Type Intermediates during Photoreaction of trans-4‘-Benzyl-5-styrylfuran

“…Laser Flash Photolysis. Laser flash photolysis (LFP) experiments were carried out using the third harmonic oscillation (355 nm) from a mode-locked Nd 3+ :YAG laser (30-ps fwhm, 10 Hz) seeded by a picosecond diode laser (1064 nm, 5-ps, 100 MHz) and a Nd 3+ :YAG laser (355 nm, 5-ns fwhm) as an excitation source. − The monitor light was obtained from a 450-W Xe lamp synchronized with the laser flash. The laser beam was perpendicular to the monitor light.…”

Synthesis of Fréchet-type Dendrimers with Tripodal Core via Staudinger/Aza-Wittig Reactions

“…The poly(benzyl ether) dendrons, now frequently referred to as Fréchet-type dendrons, was selected because they are relatively readily accessed and exhibit the chemical stability associated with ether linkages. [19][20][21][22][23][24][25][26][27][28] Here we present the convergent synthesis of tripodal Fréchet-type dendrimers by trimerization of aldehyde-dendrons via Staudinger/ aza-Wittig reactions using tripodal core, 1,3,5-tris-(3-azidopropoxy)-benzene.…”