Transition-metal chromophores,

ECL from inorganic chromophores has been observed from a variety of transition metal complexes of ruthenium, osmium, palladium, platinum, and a few other transition metal chromophores, some of which are listed in Tables 2 and 3. For example, ECL has been observed from tetrakis(pyrophosphito)diplatinate(II),... 

The optical and PL spectroscopies have been undertaken to understand the structure-property correlations of this important family of triplet-emitting polymers. The red shift in the absorption features upon coordination of the metal groups is consistent with there being an increase in conjugation length over the molecule through the metal center. The trade-olf relationship between the phosphorescence parameters (such as emission wavelength, quantum yield, rates of radiative and nonradiative decay) and the optical gap will be formulated. For systems with third-row transition metal chromophores in which the ISC efficiency is close to 100%,76-78 the phosphorescence radiative (kr)y, and nonradiative (/cm)p decay rates are related to the measured lifetime of triplet emission (tp) and the phosphorescence quantum yield ([Pg.300]

In Refs. [315 316] a synthetic methodology was developed that allows to use transition metal chromophores such as (bipy)Re (CO)3 in studies of PET across rigid organic spacers. Intramolecular PET from 1,3-benzodithiafulvene to Re1 over 16 A via trans-1,4-cyclohexane spacer at 298 K followed by dark charge recombination was found to occur in the nanosecond time scale. 

Fig. 90. d-Transition metal chromophores fitted on dtpa (top and middle) and do3a (bottom). 

Early work on the kinetics of photoinduced ET in transition metal complex systems focused exclusively on bimolecular reactions between transition metal chromophores and electron donors or acceptors. However, concomitant with the advances in rapid photochemical kinetic methods and chemical synthetic methodology, emphasis shifted to photoinduced ET in chromophore-quencher assemblies that comprise a metal complex chromophore covalently linked to an organic electron donor or acceptor [24]. These supramolecular compounds afford several... 

Several recent studies examined photoinduced ET in dyads featuring transition metal chromophores that are dissimilar to the d6 transition metal polypyridine complexes used in the type 1 and type 2 dyads that have been discussed in the preceding sections. Since the molecular and electronic structure of the excited states involved in these systems is unique from the type 1 and type 2 dyads, results on these systems are discussed separately. 

For systems with third-row transition metal chromophores in which the ISC efficiency is close to 100% [92-94], the phosphorescence radiative and nonra-diative (A )p decay rates were related to the measured lifetime of triplet emission (Tp) and the phosphorescence quantum yield (Op) by Eqs. 3.1 and 3.2 ... 

Related to these dimetallic systems, though not involving transition metals, are the boratastilbene complexes such as a " [ H 5 C 5 B-CH =CH-CH 4 -C H =C H P h ]" (isoelectronic with distyrylbenzene chromophores) that show aggregation-dependent photophysics. In nonpolar solvents, they form tightly bound ion pairs that are poorly luminescent, but in polar solvents, or when the counter ions are encapsulated in crown ethers, strong emission is observed as a result of intramolecular charge transfer.130... 

Ley and Schanze have also examined the luminescence properties of the polymers Pq, Pio> P25> and P50 in solution at 298 K, and in a 2-methyltetrahydro-furan solvent glass at 77 K. These spectroscopic studies reveal that fluorescence from the 71,71" exciton state is observed at Amax=443 nm, 2.80 eV in the polymers P0-P50 at 298 and 77 K, but the intensity and lifetime of the fluorescence is quenched as the mole fraction of Re in the polymers is increased. This indicates that the metal chromophore quenches the 71,71" state. The quenching is inefficient even when the mole fraction is large, suggesting that interchain diffusion of the 71,71" exciton is slow compared to its lifetime [70]. Phosphorescence from the 71,71" state of the conjugated polymer backbone is observed at > max=b43 nm, 1.93 eV in P10-P50 at 77 K, and emission at Amax=690 nm, 1.8 eV is assigned to the d7i(Re) 7i oiy MLCT transition. 

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