Absorption gold-silver complexes

The physical and optical properties of the NPs used in this investigation are described in Table 6.1. The optical absorption properties of the ruthenium dye complex are also detailed in the table. It can be seen that there is good overlap between 7 of the pure silver and alloy NPs and the absorption band of the complex, while the gold NPs lie outside the absorption peak and are used as a negative control. The dependence of the excitation spectra of the dye complex on NP-dye distance is shown in Figure 6.14 for the case of the pure silver NPs. Also included in the figure is the excitation spectrum for the complex coated on the PEL layer in the absence of NPs. From Table 6.1, it can be seen that there is very good overlap between 7 of the silver NPs and the dye absorption band which constitutes the optimum plasmonic enhancement condition for the case of excitation enhancement. 

Optical properties of gold nanorod arrays have been studied and were found to be dominated by surface plasmon modes superimposed on interference effects [99]. The formation of a surface complex composed of molecules (e.g. pyridine or pyr-azine) strongly bound to silver formed during oxidation-reduction electrode potential cycles is evident in ER spectra shown in Fig. 5.18. They show pronounced absorptions not found with the respective molecules in solution. 

The photophysical properties of another trinuclear silver(I) complex [Ag3([i3-dppnt)3] (38a) have also been studied [115]. The complex shows absorption bands at 238 and 367 nm in CH2CI2. The emission spectrum of the complex in CH3CN shows an emission band at 550 nm (T6 = 5.0 ps) at room temperature. The phosphorescent state has been assigned to be ligand-centered in nature. The X-ray crystal structure of the dinuclear gold(I) counterpart shows that a potassium ion is encapsulated in the macrocyclic cavity, forming the complex [Au2K(p3-dppnt)j + (38b) [115]. 

A number of recent papers report a dramatic increase in luminescence of diheptyl-bipyridyl-diol [45], organic dyes, and other species in the presence of silver [33,56-59], gold [60], and copper [61] NPs (plasmons) compared with the luminescence of the same complex without plasmons. The absorption coefficient of the NPs is six orders of magnitude higher than that of organic molecules. These papers provide a promising approach to increase the efficiency of LSCs. 

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