Charge-transfer complexes photoluminescence

Owing to the unique host-guest properties of calixarene macrocycles, calixarene-functionalized silica particles were used as cation-selective receptor colloids [81], and separator of lanthanides and actinides [82]. Calixarenes were also used for the syntheses of Ru, Pt and Pd NPs [83-85]. Furthermore, photoluminescence and charge-transfer complexes of calixarenes and calix[4]arene-based glycoclusters were grafted onto the surface of Ti02 NPs [64, 86]. 

The photoluminescence of lattice oxide ions of transition-metal oxides mixed or supported on conventional carriers has also been reported (160b). The luminescence is shown to occur from oxo complexes (M04)" (M = V, Mo, W, Cr) in which the transition-metal ion exists in a high oxidation state with a d° electronic configuration. Since the d orbitals of the transition-metal ion are not occupied and therefore the d-d transitions impossible, S0 -)-S charge-transfer electronic transitions occur in the oxo complexes upon absorption of light. The result is that an electron is transferred from a filled molecular orbital localized mainly on the O2 anions to a d orbital of the transition-metal ion. This leads to the formation of an excited singlet electronic state S, with two unpaired electrons, in which the total electron spin,... 

The photoluminescence of dipyridophenazine complexes of ruthenium ) in the presence and absence of DNA has been well-characterized (38-40, 46-52). Excitation of the dppz complexes with visible light (440 nm) leads to localized charge transfer from the metal center (39, 40). In aqueous solution, the emission resulting from the metal-to-ligand charge-transfer excited state is deactivated via nonradiative energy transfer... 

The Franck-Condon analysis of the vibrational fine structure of the photoluminescence spectrum of the anchored vanadium oxide observed at 77 K indicates that the equilibrium V-0 bond distance of the vanadyl group is elongated in the charge-transfer excited state by 0.013 nm compared with the ground state value (725). UV irradiation of the anchored vanadium oxides at 280 K in the presence of CO led to the photoformation of CO2. Since the photoformation of CO2 from CO is accompanied by the removal of oxygen from the oxide (i.e.. the photoreduction of the oxide), such an elongation of the equilibrium nuclear distance of the V-0 bond in the excited state is closely associated with the facile photoformation of CO2 on the anchored vanadium oxides. In other words, the O hole trapped centers in the electron-hole pair state of the (V -0 ) complex exhibit a high reactivity similar to 0 anion radicals 66). 

Luminescent coordination compounds continue to attract considerable attention. Zink recently reported a new mixed-ligand copper(I) polymer that shows interesting photoluminescence (232). The complex [CuCl(L44)Ph3P] consists of a one-dimensional chain lattice of metal ions bridged by both Cl" ions and pyrazine molecules. The compound shows conductivity of less than 10-8 S cm 1. The absorption spectrum of the complex shows a band at 495 nm, which could be interpreted as the promotion of an electron from the valence band to the conduction band. On the basis of resonance Raman spectra, the lowest excited state in the polymer is assigned to the Cu(I)-to-pyrazine metal-to-ligand charge-transfer excited state. 

UV-irradiation of Mo-MCM-41 in the presence of CO alone and its subsequent evacuation at 293 K led to an efficient quenching of the photoluminescence. Moreover, no ESR signals due to the Mo " ions were detected under UV-irradiation, suggesting that the charge transfer excited triplet state of the [Mo " - O ] complex reacts with CO, leading to the formation of Mo ions as well as CO2. E qjosure of the photo-reduced Mo ions into NO molecules led to the formation of N2O under dark conditions [7]. In fact, after subsequent evacuation, the photoluminescence intensity recovered, althou not to its original intensity due to the formation of such carbonyl species as [Mo - CO], which decompose only upon heating at temperatures above 373 K [6-10]. In fact, the exposure of NO or N2O onto Mo ions imder dark conditions led to the formation of N2O and N2, respectively. After the subsequent evacuation of the catalyst, the photoluminescence intensity recovered by the oxidation of... 

Significant changes in the ligand-to-metal charge-transfer transitions and the f-f transitions in the electronic spectra of (CjHjljYb are observed, when bases like pyrrolidine, triethylphosphine, tetrahydrofuran, or tetrahydrothiophene are added to the complex in benzene solution (Schlesener and Ellis, 1983). The photoluminescence of (C5H5)3Tb and (CH3CjH4)3Tb in tetrahydrofuran solutions have been studied at different temperatures (Brittain et al., 1983). 

The metal-to-ligand charge transfer photochemistry of copper(I) diimine complexes has been studied for 20 years. McMillin and co-workers first repotted the photoredox chemistry of [Cu(dmp)2]BF4 in 1977 [92]. The same research group has also reported the photoluminescence properties of different copper(I) diimine complexes. One of the characteristics of this class of complexes is that Lewis... 

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