Fluorescence quantum yield determination

Table 4.4 The effect of the internal heavy atom effect on the fluorescence efficiency of naphthalene and its derivatives. Fluorescence quantum yields determined in solid solution at 77K...

Fluorescence quantum yields determined in solid solu-... 

We have studied this problem using first rhodamines 101 and 6G and later sul-forhodamine 101, adsorbed onto microcrystalline cellulose. After detailed concentration studies, we concluded that these two compounds could be used as reference compounds for fluorescence quantum yield determination of probes on solid surfaces [81]. Later this method was extended to studies of other surfaces and other molecules [15,16, 82, 88,102-104]. 

Sulforhodamine 101 and rhodamine 6G were further used for fluorescence quantum yield determination on different silica surfaces [7]. Silicas with controlled pore (22, 25,40, 60, 100, 150 A), and particle sizes were used. A system-... 

TPA cross-section 1 GM = 10 ° cm sec photon" measured in two-photon fluorescence method with 80 fs pulse laser. Fluorescence quantum yield determined relative to fluorescin in 0.1 N NaOH. 

The LIF technique is extremely versatile. The determination of absolute intermediate species concentrations, however, needs either an independent calibration or knowledge of the fluorescence quantum yield, i.e., the ratio of radiative events (detectable fluorescence light) over the sum of all decay processes from the excited quantum state—including predissociation, col-lisional quenching, and energy transfer. This fraction may be quite small (some tenths of a percent, e.g., for the detection of the OH radical in a flame at ambient pressure) and will depend on the local flame composition, pressure, and temperature as well as on the excited electronic state and ro-vibronic level. Short-pulse techniques with picosecond lasers enable direct determination of the quantum yield [14] and permit study of the relevant energy transfer processes [17-20]. 

Chiral dendrimers based on oligonaphthyl cores and Fr chet-type poly(aryl ether) dendrons have been investigated [44]. The absolute configuration of these dendrimers remains the same as that of their chiral cores. Both the nature of the core and the generation play a role in determining the fluorescence quantum yield. 

Stabilisers are usually determined by a time-consuming extraction from the polymer, followed by an IR or UV spectrophotometric measurement on the extract. Most stabilisers are complex aromatic compounds which exhibit intense UV absorption and therefore should show luminescence in many cases. The fluorescence emission spectra of Irgafos 168 and its phosphate degradation product, recorded in hexane at an excitation wavelength of 270 nm, are not spectrally distinct. However, the fluorescence quantum yield of the phosphate greatly exceeds that of the phosphite and this difference may enable quantitation of the phosphate concentration [150]. The application of emission spectroscopy to additive analysis was illustrated for Nonox Cl (/V./V -di-/i-naphthyl-p-phcnylene-diamine) [149] with fluorescence ex/em peaks at 392/490 nm and phosphorescence ex/em at 382/516 nm. Parker and Barnes [151] have reported the use of fluorescence for the determination of V-phenyl-l-naphthylamine and N-phenyl-2-naphthylamine in extracted vulcanised rubber. While pine tar and other additives in the rubber seriously interfered with the absorption spectrophotometric method this was not the case with the fluoromet-ric method. 

We see then that the relative fluorescence quantum yield can be determined by measuring the areas under the fluorescence bands of the sample and the fluorescent standard. However, these spectra must be corrected before their true areas can be determined. Several factors are responsible for this. The most important of these are the phototube and monochromator responses. For most phototubes the maximum response occurs within a limited wavelength range, falling off rather sharply in some cases at the short-and long-wavelength ends. This is illustrated in Figure 2.14. Similarly,... 

In practice it is much simpler to determine the relative quantum yield of fluorescence than the absolute quantum yield (see Table 2.1). This is done by comparing the fluorescence intensity of a given sample to that of a compound whose fluorescence quantum yield is known. For this one must... 

Once the fluorescence quantum yield has been determined, all that is required to calculate the fluorescence rate constant kf is the fluorescence lifetime rf. Direct measurement of this quantity, like the measurement of the fluorescence quantum yield, is difficult, in this case because of the short lifetime of the fluorescent state (shorter than the normal flash from a flash lamp ). There are, however, several methods which have been developed to determine fluorescence lifetimes and these will be the subject of this section. 

We have now seen how fluorescence quantum yields and lifetimes are experimentally determined, along with some of the strengths and weaknesses of the methods used. For anthracene these constants have been determined to be... 

Acridine and its derivatives are also fused nitrogen heterocycles similar to acridones, which display a high fluorescence quantum yield and possess the ability to intercalate tightly, though reversively, to the DNA helical structure [73], with large binding constants [74]. As a result, acridine dyes are recognized in the field of the development of probes for nucleic acid structure and conformational determination [75-77]. 

As seen from (1) and (2), intermolecular processes may reduce essentially the lifetime and the fluorescence quantum yield. Hence, controlling the changes of these characteristics, we can monitor their occurrence and determine some characteristics of intermolecular reactions. Such processes can involve other particles, when they interact directly with the fluorophore (bimolecular reactions) or participate (as energy acceptors) in deactivation of S) state, owing to nonradiative or radiative energy transfer. Table 1 gives the main known intermolecular reactions and interactions, which can be divided into four groups ... 

However, the formation of these products does not appear to play a critical role in the decision as to whether the 425 nm and 480 nm maxima are due to different states of the same molecule or to different compounds. It was reported that special care was taken to ensure the purity of luminol and of 3-aminophthalate 109>. In commercially available 3-amino-phthalic acid a yellowish impurity exhibiting brilliant green fluorescence was detected 109> this substance also formed in neutral solutions of pure 3-amino phthalic acid and crystallized from these solutions in yellow crystals. The structure of this substance was determined to be 53 its absorption spectrum has a maximum at 388 nm the fluorescence maximum is at 475 nm, with a fluorescence quantum yield of about 0.75 in DMF i 9). 

In 1888, Walter studied the quenching of fluorescence, by the concentration effect, of fluorescein solutions. Nicols and Merrit observed in 1907, in solutions of eosine and resoruflne, the symmetry existing between their absorption and fluorescence spectra. In 1910, Ley and Engelhardt determined the fluorescence quantum yield of various benzene derivatives, values that were still referred to until recent years [18], The works by Lehmann and Wood, around 1910, marked the beginning of analysis based on fluorescence [4],... 

S. Hamai and F. Hirayama, Actinometric determination of absolute fluorescence quantum yields, J. Phys. Chem., 87 83-89, 1983. 

The method of Kato and Nakai (27) for determining protein surface hydrophobicity was adapted for evaluating procyanidin binding to BSA and Gl. The procedure is based on the fact that the fluorescence quantum yield of cis-parinaric acid increases 40-fold when cis-parinaric acid enters a hydrophobic environment from a hydrophilic environment. The digestion of BSA by trypsin in the presence of procyanidin dimer, procyanidin trimer and black bean procyanidin polymer was evaluated by discontinuous sodium dodecyl sulfate (SDS) slab gel electrophoresis and a picryl sulfonic acid (TNBS) assay (28). 

Methods. Absorption spectra were recorded using an Hitachi model 150-20 spectrophotometer/data processor system. Uncorrected steady-state fluorescence emission spectra were recorded using a Perkin-Elmer MPF-44A spectrofluorimeter. These spectra were collected and stored using a dedicated microcomputer and then transferred to a VAX 11/780 computer for analysis. Fluorescence spectra were corrected subsequently for the response characteristics of the detector (21). Values of the fluorescence quantum yield, <) , were determined relative to either quinine bisulfate in IN H2S04 )>f =... 

Outline the essential features needed to determine a fluorescence quantum yield and a phosphorescence quantum yield. 

The fluorescence quantum yield of a compound may be determined by comparing the area under its fluorescence spectrum with the area under the fluorescence spectrum of a reference compound whose fluorescence quantum yield is known. The spectra of both compounds must be determined under the same conditions in very dilute solution using a spectrometer incorporating a corrected spectrum capability, in order to overcome any variation in detector sensitivity with wavelength. 

The value of the phosphorescence quantum yield can be determined by measuring the total luminescence spectrum under steady irradiation. If the fluorescence quantum yield is known then the phosphorescence quantum yield may be found by comparing the relative areas under the two corrected spectra. 

Grabolle M, Spieles M, Lesnyak V, Gaponik N, Eychmiiller A, Resch-Genger U (2009) Determination of the fluorescence quantum yield of quantum dots suitable procedures and achievable uncertainties. Anal Chem 81 6285-6294... 

Box 3.3 Determination of fluorescence quantum yields from fluorescence spectra wavelength scale or wavenumber scale ... 

Fluorescence quantum yields are usually determined by integration of the fluorescence spectrum (and subsequent normalization using a standard of known fluorescence quantum yield in order to get rid of the instrumental factor k appearing in Eqs 3.17 or 3.18 see Chapter 6). In practice, attention should be paid to the method of integration. 

Proper correction of the emission spectrum is a prerequisite for the measurement of the fluorescence quantum yield of a compound. Quantum yields are usually determined by comparison with a fluorescence standard4, i.e. a compound of known quantum yield that would ideally satisfy the following criteria (Demas, 1982) ... 

It should be noted that the accuracy of the determination of fluorescence quantum yields cannot be better than 5-10%, due to the small additive errors relevant to the absorbances at the excitation wavelength, the correction factors of the detection system and the quantum yield of the standard. 

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