Dendrimer multichromophoric

Scheme 6 Synthesis of 4PMI-TDI based dendrimer multichromophore 31...

I., Beljonne, D., Champagne, B., Mullen, K., Sauer, M., Hofkens, J. andDe Schryver, F. C. (2004) Multichromophoric dendrimers as single-photon sources a single-molecule study. J. Phys. Chem. B., 108, 16686-16696. 

Serin JM, Brousmiche DW, Frechet JMJ (2002) Cascade energy transfer in a conformation-ally mobile multichromophoric dendrimer. Chem Commun 21 2605-2607... 

The dye-loaded dendrimer 110 can be detected by means of single-molecule fluorescence.48,57,281,282 This multichromophoric system was embedded into a thin polymeric film at very low concentrations so that individual dendrimer molecules could be studied by far-field fluorescence microscopy at room temperature. Temporal fluorescence intensity fluctuations, fluorescence spectra, and decay times were measured separately or simultaneously. Collective on/off jumps of the fluorescence intensity as well as different emissive levels were observed for single dendrimer molecules with eight perylenemonoimide chromo-... 

From the small difference in the spectral width (vide supra), the assumption of an excited state excimer-like (or dimer) chromophore-chromophore interaction is possible but not conclusive. Better insight into the extent of excimer-like emission is obtained from the fluorescence decays, where only for the multichromophoric dendrimers is a long decay component of 7.4 ns observed along... 

From fluorescence depolarization measurements, anisotropy relaxation times and the associated anisotropy values have been determined for p-C2P1 p-C2P2, p-C2P3, and / -C2P. For the dendrimers with more than one chromophore, a two-exponen-tial function was found to be necessary to fit the experimental anisotropy decay traces (Table 1.2). The multichromophoric dendrimers present two-exponential decays in the anisotropy traces. The fast component (410 ps to 280 ps) of the anisotropy decay (Table 1.2) is found to decrease from p-C2P2 to p-C2P4. Contrary to the meta-substituted dendrimers m-C 1 P , the sum of the / , is now always close to the limiting value of the anisotropy even if 11 is larger than one. 

In contrast to the monoexponential anisotropy trace of monochromophoric p-CIP], the corresponding traces of the multichromophoric dendrimers p-ClP3 and p-C1P4 reveal a second and fast anisotropy decay component on the order of 50-80 ps (Table 1.1). Within the framework of the Forster... 

This component is found in first and second generation dendrimers discussed here as well in the mono- and multichromophoric ones and is a combination of various processes resulting from the static and dynamic response of the environment of the chromophore [32]. Also, a fast relaxation of vibrationally excited levels (max. 2000 cm ) of the first singlet excited state in the peryleneimide cannot totally be excluded as a part of this component [32]. 

To study the influence of the number of chromophores attached to the den-drimer on this second component, the multichromophoric compounds p-C IP3 and P-CIP4 were also studied. As can be seen in Figure 1.19a, the typical shape and wavelength dependence of the partial amplitude is persistent for all three dendrimers, but an additional positive shift can clearly be observed which increases with the number of chromophores. This clearly indicates the contribution of more than one process to this second kinetic component, meaning a more complex attribution compared to the one in the monochromophoric compound. Thus, for the interpretation of these results, two different contributions 2a and 2b to this component are assumed, which are related to different kinetic processes,... 

The data of the multichromophoric dendrimers (p-ClP4 shown) contain the typical dependence of an annihilation process, while those of the monochromophoric p-CIPi do not exhibit excitation energy dependence variations (Fig. 1.21a, b). 

The short time scale dynamics have been studied by means of femtosecond fluorescence upconversion. For all dendrimers these measurements revealed size-independent kinetic processes related to an internal vibrational redistribution, a vibrational/solvent relaxation. Singlet-singlet annihilation, only present in the multichromophoric compounds, was established by an excitation energy-dependent study. It has been shown that this type of process contributes to a larger extent in the para-substituted dendrimers compared to the meta-substituted ones. These differences between the meta- and para-substituted dendrimers... 

Generally speaking, an antenna for light harvesting is an organized multicomponent system in which several chro-mophoric molecular species absorb the incident light and channel the excitation energy to a common acceptor component. Artificial antenna systems based on porphyrin arrays [63], multichromophoric cyclodextrins [64], polynuclear metal complexes [65, 66], dendrimers [66-68], and polymers [69, 70] have been reported. In all these systems, the chromophoric units are connected by means of covalent... 

Scheme 26 Multichromophoric dendrimer with porphyrin core by Fr het and coworkers [77]...

Furuta, R, J. Brooks, M.E. Thompson, and J.M.J. Frkhet. 2003. Simultaneous light emission from a mixture of dendrimer encapsulated chromophores A model for single-layer multichromophoric organic light-emitting diodes. J Am Chem Soc 125 13165-13172. 

Metivier R, Kulzer F, Weil T, Mullen K, Basche T (2004) Energy transfer rates and pathways of single donor chromophores in a multichromophoric dendrimer built around a central acceptor core. J Am Chem Soc 126 14364... 

Hofkens J, Mans M, Gensch T, Vosch T, Cotlet M, Kohn F, Herrmatm A, Mullen K, De Schryver F (2000) Probing photophysical processes in individual multichromophoric dendrimers by single-molecule spectroscopy. J Am Chem Soc 122 9278... 

---