Quenching, luminescence

The role of disorder in the photophysics of conjugated polymers has been extensively described by the work carried out in Marburg by H. Bassler and coworkers. Based on ultrafast photoluminescence (PL) (15], field-induced luminescence quenching [16J and site-selective PL excitation [17], a model for excited state thermalizalion was proposed, which considers interchain exciton migration within the inhomogenously broadened density of states. We will base part of the interpretation of our results in m-LPPP on this model, which will be discussed in some detail in Sections 8.4 and 8.6. 

MEH-PPV and P3MBET, were used. As a measure of the efficiency of the photo-induced charge transfer, the degree of luminescence quenching and the ratio of the charged photoexcitation bands to the neutral photoexcitation bands were taken. These two numbers are plotted in Figure 15-15 versus the electrochemical reduction potential. A maximum in the photoinduced electron transfer was determined for Cbo. 

These are chemically independent of Eqs. (11-51) and (11-52). Each follows in time after the quenching event. The back reactions do not involve luminescent quenching, and so they are generally studied by absorption measurements. In these cases the values17 are 53 = 5 x 106 Lmol-1 s-1 and 54 = 4.5 X 107 Lmol-1 s-1. 

Time-resolved luminescence quenching measurements using the probe Tb(pyridine-2,6-dicarboxylic acid)i and the quencher bromophenol blue show the existence of micellar clusters in AOT-based w/o microemulsions. The fast exchange appearing over several microseconds was attributed to intracluster quenching, whereas the slow exchange on the millisecond time scale was attributed to intercluster exchange [243]. 

McMurray L, Holmes AJ, Kuperman A, Ozin GA, Ozkar S (1991) IntrazeoUte semiconductors sodium-23 MAS NMR, thallium(l+) luminescence quenching and far-IR studies of acid-base precursor chemistry in zeolite Y. J Phys Chem 95 9448-9456... 

Anion concentrations can also be monitored through lanthanide luminescence. Once again, a wide range of pathways can be responsible for luminescence quenching. For instance, complex (60) with a pendant phenanthridinium group exhibits halide ion-dependent luminescence properties as a result of collisional quenching of the phenanthridinium-centered singlet state by halide ions.165... 

Bacon J.R., Demas J.N., Determination of oxygen concentrations by luminescence quenching of a polymer-immobilized transition-metal complex, Anal. Chem. 1987 59 2780. 

Demas J.N., DeGraff B.A., Xu W., Modeling of Luminescence Quenching-Based Sensors Comparison of Multisite And Nonlinear Gas Solubility Models, Anal. Chem. 1995 67 1377-1380. 

Prevention of interchain interactions (and resulting luminescence quenching) by sterically hindering substituents... 

In the presence of earlier generations, the luminescence quenching of aqueous solutions of Ru(L)32+ by methyl viologen (Figure 13.11) was found to follow Stern-Volmer bimolecular kinetics with a quenching constant /cq 5 x 109 M-1s-1, typical for the bimolecular quenching in homogeneous solutions. This... 

Trigonal ML3 metal complexes exist as optically active pairs. The complexes can show enantiomeric selective binding to DNA and in excited state quenching.<34) One of the optically active enantiomers of RuLj complexes binds more strongly to chiral DNA than does the other enantiomer. In luminescence quenching of racemic mixtures of rare earth complexes, resolved ML3 complexes stereoselectively quench one of the rare earth species over the other. 35-39 Such chiral recognition promises to be a useful fundamental and practical tool in spectroscopy and biochemistry. 

We focus on luminescence quenching based sensors, but many of the principles are generic. Quenching-based oxygen detectors are probably the most mature. In homogeneous media with only a single component exponential decay the intensity and lifetime forms of the Stern-Volmer equations are ... 

E. R. Carraway, J. N. Demas, and B. A. DeGraff, Luminescence quenching mechanism for microheterogeneous systems, Anal Chem. 63, 332-336 (1991). 

Fig. 12. Rate constants of luminescence quenching by GMP for a series of complexes as a function of the reduction potential of their MLCT states, [adapted from Lecomte J-P. (1992) Ph.D. thesis, Brussels, Belgium] From the left to the right Ru(HAT) , RuCHATl TAP , Ru(TAP)2HAT ", Ru(TAP)i Ru(bpz)i +, RuidiCHjTAP) RufHATjjphen RufHATljbpy, Ru(TAP)2bpy2+, Ru(phen)2HAT Ru(bpy)2HAT"+...

Interestingly, the correlation of the luminescence quenching by the mononucleotides and polynucleotides with the occurrence of a photoelectron transfer process examined by flash photolysis, has been found [73,95] for the whole series of Ru(II) complexes with TAP and HAT ligands discussed in Sect. 4.1. As will be developed in Sect. 5., this photoelectron transfer with polynucleotides is also connected to enhanced yield of strand breaks and the appearence of adducts on DNA. 

---