| Abstract
| - The synthesis and charge transfer properties of triarylamine−oligothiophene−perylenemonoimide dendrimers,TPA(T2-PMI)3 and TPA(T4-PMI)3, are described. The fluorescence quantum yields indicate strong emissionquenching by electron transfer [ΦTHF = 0.004 for TPA(T2-PMI)3, ΦTHF = 0.003 for TPA(T4-PMI)3, andΦTHF = 0.8 for PMI]. Moreover, with the increase of the solvent polarity, the quantum yields decrease indicatingthat the A+•D-• (acceptor/donor) couple is more stabilized. The femtosecond transient absorption spectrashow a very fast charge separation process (≈2 ps; kcs ≈ 5 × 1011 s-1) and a charge recombination of morethan 1 order of magnitude slower (≈50 ps; kcr ≈ 2 × 1010 s-1), as observed from the rise time and decay ofthe radical anion and radical cation absorption bands. The analysis of the transient absorption spectroscopyand of the energetics of the process using Marcus theory indicates that in the electron transfer process thethiophene unit is the first electron donor. The triarylamine is not functioning as a second electron donor, asalso substantiated by the absence of an effect of the addition of acid on the emission intensity of the dendrimers.The presence of the triarylamine and/or the proximity of the oligothiophenes does improve the donor capabilitiesof the oligothiophene unit slightly and enhances its conjugation as seen in the absorption spectra and thetransients of the radial cations. These results can be used for a better design of molecular materials for, e.g.,photovoltaic applications.
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