Temperature dependence, photophysical

Temperature dependence, photophysical processes, 302-3 stereoselectivity, 326-27 Telra-t-butyltetrahedrane. 385 Tetracene, 254 absorption spectrum, 72, 103 Tetracene radical anion and cation. 103 Tetracycioociene, 423 Tetramethylcyclobutane, 406 TetramethyM,2-dioxeiane, 428. 482-83 Tetrameihylethyiene, 326-27 Tetranitromethane, 465 n.a.a a -Tetraphenylbenzocyclobuiene,... 

The validity of the above conclusions rests on the reliability of theoretical predictions on excited state barriers as low as 1-2 kcal mol . Of course, this required as accurate an experimental check as possible with reference to both the solvent viscosity effects, completely disregarded by theory, and the dielectric solvent effects. As for the photoisomerization dynamics, the needed information was derived from measurements of fluorescence lifetimes (x) and quantum yields (dielectric constant, where extensive formation of ion pairs may occur [60], the observed photophysical properties are confidently referable to the unperturbed BMPC cation. Figure 6 shows the temperature dependence of the... 

The first photophysical investigation performed on stereochemically pure metal-based dendrimers having a metal complex as the core is that concerning the tetranuclear species based on a [Ru(tpphz)3]2+ core (tpphz=tetrapyrido[3,2-a 2, 3 -c 3",2"-h 2",3"j]phenazine) [67]. Dendrimer 45 is an example of this family. In this compound, two different types of MLCT excited states, coupled by a medium- and temperature-dependent photoinduced electron transfer, are responsible for the luminescence behavior. However, the properties of all the optical isomers of this family of compounds are very similar. This finding is also in... 

Even when the d-d state is at much higher energy than the emitting level, it can still be of paramount importance in the photophysics and photochemistry of the system. Indeed, a major contributor to the temperature-dependent loss of emission intensity in luminescent metal complex based sensor materials is nonradiative decay via high-energy d-d excited states.(15) The model for this is shown in Figure 4.4A. The excited state lifetime is given by... 

The temperature dependence of the dual fluorescence of DMABN as shown in Fig. 2.1 displays several characteristic features. The short wavelength B band at around 350 nm shows an intensity minimum at a certain temperature Tm around 200 K, whereas the quantum yield of the long wavelength A band slightly but monotonically increases with temperature. Thus, above Tm, the total fluorescence quantum yield increases with temperature, a feature which is rather uncommon in photophysics. 

Intramolecular bridging can also be used to suppress the P state selectively. This has dramatic photophysical consequences DCS-B34 shows fluorescence quantum yields of about 80% and no sign of intramolecular fluoresrence quenching [35] but some indication of a temperature-dependent A E equilibrium. The high quantum yield of this compound shows that the TICT emission is allowed in this case. The same can be concluded for DCS from the sizeable quantum yields at the lifetime maximum near — 90 °C in ethanol [35]. A possible explanation are narrow minima in kf or f (case II of Fig. 14). First results for compounds like DM-DS-B34 sterically confined to the neighbourhood of a perpendicular conformation show a large reduction in fluorescence quantum yield with respect to the unconfined case (DS-B34). 

Optical measurements have been reported for [Ru(bipy)3], [Ru(bipy)2(biq)f, and [Ru(biq)3] (biq = 2,2 -biquinolyl) together with the temperature dependence (84—330 K) of the luminescence emission. The behaviour of the three complexes is rationalized in terms of states derived from a simple orbital model. A description of the photophysical and redox properties of the luminescent complexes [RuLL L ] (where L = 2,2 -bipyridyl, L = 2,2, 2"-terpyridyl, and L" = phenothiazine, N-methylphenothiazine, thian-threne, or H2O) has appeared, and this suggests that states other than the luminescent state are populated. Coupling between dissimilar ligands in the excited states of [Ru(bipy) (phen)3 f, [Ru(bipy) L3 and... 

Phillips, D., Roberts, A. J., Soutar, I. Transient decay studies of photophysical processes in aromatic polymers. V Temperature dependence of excimer formation and decay in copolymers of 1-vinyl naphthalene. As yet unpublished 1980... 

Emeline A. V., Polikhova S., Andreev N., Ryabchnk V. K. and Serpone N. (2002b), Photoinduced processes in heterogeneons gas-solid systems. Temperature dependence (100-600 K) and modelling of a snrface chemical reaction on zirconia that triggers photophysical events in the solid , J. Phys. Chem. B 106, 5956-5966. 

These data, taken at face value, might be interpreted as being indicative of a temperature dependence of by comparison of equations (3) and (5), However, the photophysics of the... 

The recovery time following upon bleaching induced by Si-Sji absorption of p-terphenyl in cyclohexane at room temperature is found to be about 380 ps. The temperature dependence of photophysical processes in perylene, tetracene, and some derivatives is shown to arise from thermal activation of the S1-T2 intersystem crossing process and also for the Si-Sq internal conversion, which is particularly important in rubrene. ... 

In a study of the photophysics of 45-A CdS clusters [62] O Neil et al. observed a broad luminescence band from 400nm to over 800 nm. The luminescence decay kinetics is multiexponential at all wavelengths, consisting of two distinct time regimes. The fast decay has a lifetime of 500ps and is weakly temperature dependent. The slower decay has a lifetime, on the order of 20 ns, and is strongly dependent on temperature. The authors invoke the three-level thermal equilibrium model to interpret the results. The electron is assumed to be trapped shallowly at D. Luminescence is assumed to come from recombination between detrapped electrons and trapped holes [62]. The gap between the LUMO and the top of the trap levels is estimated to be 3meV. 

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