Porphyrin luminescence

It has been found that whereas Cu11 porphyrins luminesce, the Ag" complexes do not. By an examination of electronic absorption spectra, emission spectra, redox potentials and near-IR absorption data, it was proposed that this could be rationalized on the basis of the energy of the big (dx2 yi) orbital. Extended Hiickel molecular orbital calculations predicted that the d-n transition would be above the lowest (n, jt ) levels for Cu11 but below them in the Agn complexes. The near-IR absorptions found for Ag11 were attributed to CT transitions.554... 

Porphyrin-fullerene conjugates attract wide attention for their intramolecular energy and electron transfer properties [87, 88]. By attachment of the porphyrin to two points on the Cgo surface, the interchromophoric spatial relationship in the cyclophane-type molecular dyads trans-2 ( )-52 [67] and trans-1 54 [68] (Scheme 7-8), which controls both energy and electron transfer, is rigorously defined. In the two systems, as well as in the fullerene-porphyrin conjugate 58 [75] (Scheme 7-9), the close proximity between fullerene and porphyrin chromophore leads to a nearly complete quenching of the porphyrin luminescence, presumably as a result of efficient energy transfer between the porphyrin donor and the fullerene acceptor. 

As just mentioned, phosphorus porphyrins have unique photochemical properties. Their photophysics is also interesting. Emitter-quencher assemblies based on porphyrin building blocks have attracted attention due to their potential to serve as models in photosynthetic research (see [90] for an example) or for the development of photoswitches that could be used for the fabrication of molecular electronic/optical devices. In this context, Maiya and coworkers constructed a P(VI) porphyrin system 59b with two switchable azobenzene groups positioned in the apical positions of the pseudo-octahedral phosphorus atom [92]. Photoswitch ability (luminescence on/off) was demonstrated as... 

Optical sensors for oxygen are among the few sensors, which have found practical application for process-monitoring and clinical diagnostics. They are generally based on compounds such as platinum porphyrins or ruthenium phenanthroline derivatives (Table 17) which show a decrease in luminescence upon exposure to molecular oxygen15. 

Hartmann P., Trettnak W., Effects of polymer matrices on calibration functions of luminescent oxygen sensors based on porphyrin ketone complexes, Anal. Chem. 1996 68(15) 2615-2620. 

The adsorption of transition metal complexes by minerals is often followed by reactions which change the coordination environment around the metal ion. Thus in the adsorption of hexaamminechromium(III) and tris(ethylenediamine) chromium(III) by chlorite, illite and kaolinite, XPS showed that hydrolysis reactions occurred, leading to the formation of aqua complexes (67). In a similar manner, dehydration of hexaaraminecobalt(III) and chloropentaamminecobalt(III) adsorbed on montmorillonite led to the formation of cobalt(II) hydroxide and ammonium ions (68), the reaction being conveniently followed by the IR absorbance of the ammonium ions. Demetallation of complexes can also occur, as in the case of dehydration of tin tetra(4-pyridyl) porphyrin adsorbed on Na hectorite (69). The reaction, which was observed using UV-visible and luminescence spectroscopy, was reversible indicating that the Sn(IV) cation and porphyrin anion remained close to one another after destruction of the complex. 

The aim of this chapter is limited to reviewing some recent developments concerning luminescent dendrimers that can play the role of ligands and sensors for luminescent and nonluminescent metal ions, mainly investigated in our laboratories, with particular references to transition metal or lanthanide ions. We will not discuss dendrimers constituted by polypyridine metal complexes [21] and porphyrins [22] since it is outside the scope of the present paper. 

For some examples, see e.g. (a) Hogan CF, Harris AR, Bond AM et al (2006) Electrochemical studies of porphyrin-appended dendrimers. PhysChemChemPhys 8 2058-2065 (b) Jang W-D, Nishiyama N, Zhang G-D et al (2005) Supramolecular nanocarrier of anionic dendrimer porphyrins with cationic block copolymers modified with polyethylene glycol to enhance intracellular photodynamic efficacy. Angew Chem Int Ed 44 419 -23 (c) Loiseau F, Campagna S, Hameurlaine A et al (2005) Dendrimers made of porphyrin cores and carbazole chromophores as peripheral units. Absorption spectra, luminescence properties, and oxidation... 

Platinum and palladium porphyrins in silicon rubber resins are typical oxygen sensors and carriers, respectively. An analysis of the characteristics of these types of polymer films to sense oxygen is given in Ref. 34. For the sake of simplicity the luminescence decay of most phosphorescence sensors may be fitted to a double exponential function. The first component gives the excited state lifetime of the sensor phosphorescence while the second component, with a zero lifetime, yields the excitation backscatter seen by the detector. The excitation backscatter is usually about three orders of magnitude more intense in small optical fibers (100 than the sensor luminescence. The use of interference filters reduce the excitation substantially but does not eliminate it. The sine and cosine Fourier transforms of/(f) yield the following results ... 

During the last ten years, studies of luminescence and photochemistry of polypyridyl Ru(II), Rh(III) and Co(III) complexes, porphyrins and uranyl salts, in the presence of biological macromolecules such as DNA, have been the focus of increasing research work. The interest in such coordination compounds stems from their easily tunable properties. Not only their size and shape but also their... 

When molecules absorb a photon and produce an electronic excited state, the energy can be dissipated in several ways luminescence, radiationless decay to the ground state, and photochemistry. Luminescence dominated the older literature because it was easy to observe. A good review of luminescence is in Volume 3 of David Dolphin s seven-volume series The Porphyrins. Picosecond laser spectroscopy allowed for exploration of the radiationless decay pathways, particularly the initial steps that compete with luminescence and lead to photochemistry. Two principal forms of radiationless decay lead to long-term metastables ligand ejection and electron transfer. 

The photophysical properties of [Ru(TBP)(CO)(EtOH)], [Ru(TBP)(pyz)2], [Ru(TBP)(pyz)] (Fl2TBP = 5,10,15,20-tetra(3,5-tert-butyl-4-hydroxyphenyl)porphyrin) have been investigated by steady-state and time-resolved absorption and emission spectroscopies. The complexes are weakly luminescent, and the origins of this behavior is discussed.Transient Raman spectroscopic data have been reported for [Ru(TPP)(py)2], [Ru(TPP)(CO)(py), and [Ru(TPP)(pip)2] (pip = piperidine),and nanosecond time-resolved resonance Raman spectroscopy has been used to examine the CT excited states of [Ru(0EP)(py)2] and [Ru(TPP)(py)2]. " ... 

Metalloporphyrins, MP, represent derivatives of porphyrin, P, in which four pyrrole fragments are bound together by methine bridges (Fig. 13). The diversity of porphyrins is due to the possibility of variation for substituents R in the periphery of the porphyrin ring. A typical optical spectrum of a P solution is presented in Fig. 14. One can point out quite a number of characteristic bands in it. The most intensive short-wave peak in the P absorption spectrum (/max 400 nm) corresponds to the transition S0 -+ S2 and is referred to as Soret band. The extinction coefficient of this band is very large, as a rule, and amounts to 10 -106 M 1 cm-1. The less intensive long-wave bands of P absorption correspond to the S0 - Sx transition (bands I-IV in Fig. 14). Complexation with the metal results in a rise of the symmetry of the molecule, due to which MP molecules have only two bands in the long-wave part of the absorption spectra. Most of the metalloporphyrins are characterized by intense luminescence. The time of MP fluorescence decay (transition Si - S0) is short and amounts to 10"8 to 10 9 s. Besides the transition... 

In case of co-facial quinone-capped porphyrins (P and Q are linked by four tetraamidophenoxy bridges and are located at a distance of 10 A from each other), the quantum yield of charge separation is much bigger and reaches 30% for short distances between P and Q [53, 54]. Luminescence quenching via electron transfer from P to Q is observed for both singlet- and triplet-excited states of the porphyrin fragment of P-Q. The appearance of the additional channel for luminescence decay via electron transfer manifests itself in the biphase character of P-Q luminescence decay kinetics. 

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