Emission spectra group 1 metals

A first generation poly(amido amine) dendrimer has been functionalized with three calyx[4]arenes, each carrying a pyrene fluorophore (4) [30]. In acetonitrile solution the emission spectrum shows both the monomer and the excimer emission band, typical of the pyrene chromophore. Upon addition of Al3+ as perchlorate salt, a decrease in the excimer emission and a consequent revival of the monomer emission is observed. This can be interpreted as a change in the dendrimer structure and flexibility upon metal ion complexation that inhibits close proximity of pyrenyl units, thus decreasing the excimer formation probability. 1H NMR studies of dendrimer 4 revealed marked differences upon Al3+ addition only in the chemical shifts of the CH2 protons linked to the central amine group, demonstrating that the metal ion is coordinated by the dendrimer core. MALDI-TOF experiments gave evidence of a 1 1 complex. Similar results have been obtained for In3+, while other cations such as Ag+, Cd2+, and Zn2+ do not affect the luminescence properties of... 

There is a small solvent dependence for [Ru(L)3]2+complexes which depends on the structure of L. The emission spectra of the Ru(bpy)32+ is mildly sensitive to media, the Ru(phen)32+ much less so, and the Ru(Ph2phen)32+ is virtually media independent. This decreasing sensitivity to solvent perturbation is a consequence of the excitation being localized in the metal a-diimine portion of the complex (-N=C-C=N).(27) The more extended the complex, the greater the shielding of the excited portion and the smaller the solvent perturbations of the emission spectrum. In particular, the bulky phenyl groups are extremely effective at shielding the excited state from environmental perturbations. 

The appearance of nontotally symmetric modes in the emission spectrum has important ramifications to the structure of the excited state. Because they do appear, the point group of the excited state of ruthenocene is lower than Djh. The point group in the excited state must be one in which these vibrational modes are totally symmetric. The point group which satisfies this condition is C,. In this symmetry, the 445 cm ring-metal stretch and one component of the ring tilt mode are totally symmetric. The involvement of... 

Intramolecular transfers between two ehromphores separated by insulating groups can lead to absorption by one chromophore and emission from the other. Complexes of rare earths specially of Eu+3, Sm+3. Gd+3 and Dy+3 emit line spectrum characteristic of the central metal ion when absorption takes place in the ligand moeity. 

B. The effect of adding different metals ions on the emission was investigated at pH 7.4. Groups I and II ions, as well as Zn +, had no effect. Addition of Cu + ions shifted the absorption spectrum of the phenanthroline ligand slightly from 255 to 280 nm and caused a substantial quenching of the europium luminescence. This was reversed, with recovery of the europium emission, on adding EDTA solution. Comment on this. 

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