Single molecule spectroscopy, dyes

There are two important drawbacks of such an approach (1) a polarity scale based on a particular class of probes, in principle, does not account, for example, sizes of probes, which should strongly effect the interactions (2) betain dyes do not fluoresce, which restrict essentially the field of application of this approach, because in many cases, absorption spectrum could not be measured accurately (small volumes of samples, study of cells, and single molecules spectroscopy). Therefore, polarity-sensitive fluorescent dyes offer distinct advantage in many applications. 

Dye stuffs are among the oldest topics of synthetic organic and industrial chemistry, and it is exciting to follow their role in nanosciences and single molecule spectroscopy. 

The attachment of a distinct number of fluorescent dyes at the periphery of a stiff three-dimensional nanoparticle is of fundamental interest to study interactions between single chromophores in close vicinity to each other. We chose as a dye one of the rylene series, perylenemonoimide, for the decoration of our polyphenylene dendrimers due to their outstanding properties. Rylene dyes show an exceptional chemical and photochemical stability and therefore are well suited for single molecule spectroscopy (SMS) [661. 

Keywords Cholesteric phases Energy transfer Fluorophores Light-harvesting complex Organic dye molecules Quantum chemistry Semiconductor quantum dots Single-molecule spectroscopy... 

The ability of cyanines to bind to DNA has led to the development of numerous fluorescence detection methods, mostly involving dyes that exhibit significant enhancements in fluorescence quantum yield upon binding. Covalent attachment of cyanines to DNA results in fluorescent labeling of the DNA, useful for a variety of applications including gene chip analysis and single molecule spectroscopy. 

Due to the inherent stiffness of 1,4-phenylene based polymers and based on molecular modeUng calculations (see below), the question arises whether the shape of the dendrimer can be predetermined by choosing an appropriate core. This should be important for the use of dendrimers in single molecule appHca-tions, as carriers for dyes for single molecule optical spectroscopy or as building blocks for two- and three-dimensional assemblies. There are two possibiHties variation of the core and variation of the building unit. Therefore, we synthesized dendrimers based on cores with different symmetries presented in Scheme 4. 

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