Photophysics of PAMAM-Based Dendrimers of Polypyridyl Complexes of Ruthenium

Abstract

The photophysics of PAMAM (poly-amidoamine) based dendrimers (generations G0-G4) modified with (4, 8, 16, 32, and 64) pendant-[Ru(tpy) 2 ] +2 (tpy is 2,2′:6′,2′′-terpyridine) and [Ru(bpy) 3 ] +2 (bpy is 2,2′-bipyridine) chromophores have been studied in both fluid solution at 298 K and frozen glasses, at 77 K. The absorption and emission spectra, the excited-state lifetimes and quantum yields have been obtained for both families of metallodendrimers. In general and in analogy to the behavior exhibited by the discrete molecules (i.e., [Ru-(tpy) 2 ] +2 and [Ru(bpy) 3 ] +2 ), the bipyridine derivatives exhibit longer lifetimes and higher quantum yields when compared to the corresponding terpyridine complexes. Some generation dependent changes have also been observed. We have also explored the effects of solvent by comparing results in butyronitrile and dimethylacetamide with the latter being used as a mimic of the dendritic backbone. Our results suggest that for the higher generations the dendritic backbone acts as the solvent in affecting the photophysical behavior.

Determination of solvation numbers of [RuII(bpy)3] and [RuII(tpy)2] functionalized-PAMAM dendrimers adsorbed onto platinum electrode surfaces

“…As part of those investigations, we have been involved in the study of the solvent dependence of electrochemical transport, mainly through diffusion coefficients [10], as well as the solvent dependence of spectroscopic properties [11]. This, in turn, has prompted us to take a closer look at solvation, particularly solvation numbers.…”

“…Solvation can play an important role in the local environment, such as the local dielectric constant, which can, in turn, affect excited state relaxation dynamics [11].…”

Electroluminescence in Ruthenium(II) Dendrimers

“…43,44 For the sake of completeness, the main points are summarized in Table 1. The electroluminescence (EL) spectra were found to be similar to the photoluminescence (PL) spectra from spin-coated films.…”

“…The degree of self-quenching depends chiefly on the distance between the chromophores, which depends on the precise configuration of the dendrimers which is not exactly known. 42,43 We are currently investigating the spectroscopic properties of dendrimer films to gain a better understanding of the self-quenching of luminescence in these materials.…”

“…[41][42][43][44] stimulated not only by their redox chemistry but also by their photophysical behavior. In this regard, the study of dendrimers containing pendant [Ru(bpy) 3 ] +2 chromophores is of particular interest.…”