Spectroscopic investigations supramolecular assemblies

A number of different approaches can be taken to investigate the charge-injection process. The first one, outlined in the last section, is based on the absorption rise observed at about 1200 nm which is associated with the presence of electrons in TiC>2. A second method is based on the measurement of the IPCE values for the assemblies in the presence of iodide, while the third approach is based on the intrinsic spectroscopic features of the sensitizer. In this present section, the focus is on the latter two approaches since the absolute rate for charge injection is not of direct interest but simply whether or not injection is taking place. To estimate the injection and charge-separation process, the transient absorption spectra of the sensitizer in solution are compared with those obtained in the interfacial supramolecular assembly. A typical example of this approach is shown in Figure 6.17 for the compound [Ru(dcbpy)2(bpzt)] [8], (see Figure 6.7 above for the structure). 

Optical and Spectroscopic Investigations of Supramolecular Assemblies of Optoelectronic Materials... 

Finally, because this chapter is devoted to supramolecular chemistry, pH sensors or sensors for protonation-deprotonation sensitive probes are also not being considered because one usually does not consider a protonated base as a supramolecular assembly. However, a number of sensors can display a continuum of behaviors, for example, between hydrogen bonding to a receptor and a receptor deprotonation, and one needs to be quite careful about the assignment of the UV-vis spectroscopic changes. It is always a good idea to investigate even a colorimetric sensor by an independent technique such as NMR spectroscopy or isothermal microcalorimetry. 

Other triorganotin phosphinates self-assemble into chain-like, supramolecular helical arrays, 176 these include trimethyltin dimethylphosphinate, Me3Sn02PMe2, and dichlorophosphate, Me3Sn02PCl2 [529], and tri-n-butyltin diphenylphosphinate, Bu3Sn02PPh2 [530]. The self-assembly of tributyltin derivatives of phosphorus oxyacids (orthophosphates, phosphonates, and phosphinates), (Bu3Sn) 0 P(0)-Ph3 , n = 0-2, has been investigated by " Sn and P NMR and " Sn Moss-bauer spectroscopy results are indicative of intermolecular association both in solution and in the solid state [531]. On the basis of spectroscopic evidence associated structures in the solid state and in solution have also been suggested for tri-... 

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