Precursors for perylene diimide dendrimers : synthesis and photophysics
Perylene dyes are photostable and have been used in a variety of applications. However they often display aggregation effects in the solution phase, leading to concentration-dependent electroluminescent (EL) quenching, band broadening, and/or a bathochromic shift. These phenomena not only affect the EL device performance, but also impose a severe constraint on any manufacturing process in which the dopant concentration has to be precisely controlled in order to obtain reproducible chromaticity and efficiency. In this research, the first generation of a water/organic solvent soluble 3,4,9,10-Perylene Tetracarboxylic Diimide (PDIs) dendrimer (PDI1.0) was synthesized in one step in good yield. In further steps, PDI1.5 compounds were synthesized using methyl acrylate and acrylonitrile with PDI1.0. Their photophysics in solutions was studied by UV and fluorescence spectra as a function of added trifluoroacetic acid (TFA). Previous work in laboratory has demonstrated that TFA can greatly enhance the fluorescence yield of related compounds, either by reducing intramolecular quenching or breaking up aggregates (or both). The UV absorption spectra demonstrated that the addition of TFA enhances the PDI extinction coefficient, which is interpreted as reversing a hypochromic effect from aggregation. The results showed that there were two jumps in the fluorescence spectra. The first one happened as the ratio of TFA/PDI exceeds 6:1 due to the protonation of the amine and loss of intramolecular electron transfer quenching. The other one occurred at TFA/PDI ratios greater than 10⁴. We propose that this latter effect is due to aggregates that are being broken up by the relatively large amount of TFA, which may be a good solvent or co-solvent for these PDI compounds. In addition, PDI1.0 has been well characterized and its photophysics attached to SiO₂ has been studied
Perylene diimide dendrimers, Photophysics
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