Dendrons porphyrin core

In dichloromethane solutions, excitation of the chromophoric groups of the dendrons causes singlet-singlet energy transfer processes that lead to the excitation of the porphyrin core. It was found that the dendrimer 17, which has a spherical morphology, exhibits a much higher energy transfer quantum yield (0.8) than the partially substituted species 13-16 (quantum yield <0.32). Fluo-... 

When a porphyrin core is linked to four 1,3,5-phenylene-based dendrons (compounds 19-22), energy transfer from the excited dendrons to the por-... 

Figure 5. Structures of some functional dendrimers A. Dendrimer with lanthanide ion as the central core with dendrons as ligands B. Dendrimer based on metal complex C. Silicon-based ferrocenyl dendrimer and D. Dendrimer with zinc-porphyrin core...

Scheme 15 Stilbene dendrons by Burn and Samuel with DSB (35-37), distyrylanthracene (38-40), and porphyrin cores (41 and 44) [65]...

The three categories of porphyrin-containing dendrimers that will be discussed include (i) porphyrin cores surrounded by organic dendrons [66-69], (ii) dendritic arrays of porphyrins at the both core and branching points [70-72],... 

Star-shaped multi-porphyrin arrays have been constructed to mimic energy funneUng in photosynthesis. These dendrimers contain free-base porphyrin cores (Pfb) connected to four dendrons consisting of 1,3, or 7 zinc-metallated porphyrins (Pzn) embedded in an organic matrix coimected by ether linkages (Scheme 21) [70,71]. The periphery consists of methoxy-terminated poly(aryl ether) dendrons. For comparison, cone-shaped arrays consisting of Pfb cores monosubstituted with Pz dendrons were also synthesized. 

Onitsuka and Takahashi reported the synthesis and characterization of zinc porphyrin core dendrimers with platinum acetylide based dendrons... 

Scheme 25 Porphyrin core dendrimers with platinum acetylide dendrons by Onitsuka and coworkers [76]...

Scheme 25) [76]. Intramolecular energy transfer was evidenced by fluorescence of the porphyrin core observed (A-em = 617 run) upon excitation of either the MLCT band of the platinum acetyUde dendrons (A.ex = 344 nm) or the Soret band of the porphyrin core (A-ex = 435 nm). Energy transfer from the dendrons to the core was not quantitative, as significant dendron emission (A-em = 384 nm) was observed from all generations. Fluorescence from the porphyrin core at 617 nm appreciably decreased with increasing generation, and another fluorescence peak (648 nm) was observed. 

Scheme 27 Porphyrin core dendrimers with carbazole dendrons by Dehaen [78] (top) and Lu [79] (bottom)... 

A different approach to dendritic sensors involves modification of a sensor core unit with dendritic substituents to confer beneficial solubility properties. An example of a sensor core unit is the porphyrin macrocycle, a heterocycle that has been employed extensively in prototypical photochemical sensor systems. Vinogradov and co-workers have exploited the versatile photoactive porphyrin sensor unit as a fluorescence-based pH indicator for use in biological assays [73], by attaching acid terminated polyamide-ether dendrons as substituents (Figure 8.12). The two imino nitrogen atoms present in the free-base porphyrin are susceptible to stepwise protonation to afford initially a cation and then a dication, respectively. Upon protonation, both the emission and absorption fluorescence spectroscopic characteristics of the porphyrin core are subject to dramatic hypochromic shifts. This spectroscopic phenomenon formed the basis for an accurate pH indicator with potential applications in proton gradient determination studies in biological systems. 

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