Supramolecular interaction excited state

Thus, several processes may take place within supramolecular systems modulated by the arrangement of the components. These processes involve a modification of the physical and chemical processes of excited states when photoactive components are included in a supramolecular structure. Light excitation of a specific photoactive molecular subunit may also modify the electronic interactions between this subunit and other components, resulting in such phenomena as ... 

At this point, it seems that in these binudear units, which act as building blocks of supramolecular systems, the existence of different gold-gold interactions does not affect the extited states from which the emissions are produced. In other words, the emissions do not depend on the type of interactions in the complexes but only on their number or length. This is surprising since one would expect different excited states to arise from the interactions that appear as a consequence of intramolecular and intermolecular interaction, above all when the distances are quite different. This problem was first considered by Fackler and coworkers in complexes of the type... 

A similar supramolecular approach, in which both n-n stacking stacking of pyrene on the SWNT surface and alkyl ammonium-crown ether interactions were used in the self-assembly process of a fullerene derivative with SWNTs, was recently reported (Scheme 9.22).72 The nanohybrid integrity was probed with various spectroscopic techniques, , and electrochemical measurements. Nanosecond transient absorption studies confirmed electron transfer as the quenching mechanism of the singlet excited state of C60 in the nanohybrid resulting in the formation of SWNT"1"/ Pyr-NH3 + /crown- charge-separated state. 

For supramolecular assemblies, intramolecular processes may quench the emission of A to a degree which depends on the relative efficiency of the process when compared with emission. It is often useful to compare the photophysical and chemical behavior of the supramolecular species, e.g. A -L-B, with an appropriate model compound, for instance, AH, which contains the photochemically active component, A, in the absence of any units capable of interacting with A. For example, from luminescence lifetime measurements, the rate of electron transfer may be estimated by comparing the excited-state lifetime of the mononuclear model complex, tModei, with that of the supramolecular species, rsupra, by using the following equation ... 

The above result unequivocally demonstrates that the seemingly weak solvation effect can play a decisive role, which controls and even switches the stereochemical outcome of the enantiodifferentiating photoisomerization. Temperature, pressure, and solvation, which function as environmental factors to control the enantiodifferentiation in the excited state, are all entropic in nature. Probably the key is the critical control of the weak interactions involved in the exciplex intermediate, as with the biological and supramolecular interactions in... 

It should be noted that the 1,3-dimethoxybenzene and 2-naphthyl chromophoric units contained in the branches of the dendrimer are not involved in metal coordination. In some way, they belong to a second coordination sphere. If is considered a large metal complex, the absorption and emission bands of the 1,3-dimethoxybenzene and 2-naphthyl chromophoric units can formally be classified as LC. However, can be more properly viewed as a supramolecular (multicomponent) species (12). In such species, each chromophoric imit displays its own absorption spectrum since there is no appreciable interactions among them in the ground state, but in the excited state even weak interactions can cause intercomponent energy or electron-transfer processes. This kind of reasoning can also be applied to all the other systems discussed in this chapter. 

The donor/acceptor interaction introduces low-energy CT excited states whic are responsible not only for the color of these supramolecular species (due ence of broad and weak absorption bands in the visible region), but a so or... 

In the case where a chromophore or a fluorophore of a supramolecular system is involved in the association with a species, the binding ability of this system may be different in the ground state and in the excited state. This occurs when a conformational change is induced by light, or when a redistribution of charges in the excited state leads to changes in electrostatic interactions in a host-guest complex. 

All the terms in our transformed Hamiltonian were already derived by Agranovich [46] in the discussion of clusters of two-level molecules interacting via electrostatic forces. The main novelty of the proposed approach is that it is based on local (molecular) ground and excited states as obtained in the mf approximation and therefore it explicitly accounts for the dependence of the local ground and excited state on the supramolecular interactions. In the standard approach instead the term in (bl H-fc ) in Eq. (12) is disregarded 46], and the local wave functions do not depend on tire supramolecular geometry. The strength of our approach is in its ability to follow the evolution of the properties of the supramolecular systems... 

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