Luminescence molecular centers

Similarly, fluorescent silver clusters could be prepared in so called molecular hydrogels, formed by polyglycerol-b/oc -poly(acrylic acid) (PG-b-PAA), using a ratio COOH Ag of 2 1 with UV irradiation (365 nm). The emission band centered at 590 nm reached a maximum after 200 min of irradiation. The authors claim improved photostability of the clusters since they are still luminescent even after 9 h of irradiation, but it has to be mentioned that the irradiation source was weak, only 0.5 mW/cm2. They claim that it is the number of arms in the star polymer rather than the length of the arms (thus the density of COOH) that plays a crucial role in the formation of silver clusters [30]. 

Density functional theory (DFT) calculations were also carried out to assign the molecular orbitals involved in the transitions that lead to luminescence, concluding that metal centered (du )1(pu)1 or (da )1 (pa)1 excited states are responsible for the luminescence in the solid state, while in dilute solutions the luminescence arises from ira excited states in the pentafluorophenyl ligands or from ir-MMCT transitions. 

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