Fluorescence anomalous

Gruber HJ, Hahn CD, Kada G, Riener CK, Harms GS, Ahrer W, Dax TG, Knaus HG (2000) Anomalous fluorescence enhancement of Cy3 and Cy3.5 versus anomalous fluorescence loss of Cy5 and Cy7 upon covalent linking to IgG and noncovalent binding to avidin. Bioconjugate Chem 11 696-704... 

Rotkiewicz K, Grellmann KH, Grabowski ZR (1973) Reinterpretation of the anomalous fluorescence of p-N, N-dimethylaminobenzonitrile. Chem Phys Lett 19 315-318... 

K. Rotkiewicz, K. H. Grellmann, and Z. R. Grabowski, Reinterpretation of the anomalous fluorescence ofP-N,N-dimethylamino-benzonitrile, Chem. Phys. Lett. 79,315 (1973). 

V. Bonacic-Koutecky and J. Michl, Charge-transfer-biradical excited states Relation to anomalous fluorescence, Negative Sl-Tl splitting in twisted aminoborane, J. Am. Chem. Soc. 107, 1765 (1985). 

K. A. Al-Hassan and T. Azumi, The red edge effect as a tool for investigating the origin of the anomalous fluorescence band of 9,9 -bianthryl in rigid polar polymer matrices, Chem. Phys. Lett, 150, 344 (1988). 

T. Kimura, J. J. Ting, and J. J. Huang, Studies on adrenal steroid hydroxylases. Anomalous fluorescence of a tyrosyl residue in adrenal iron-sulfur protein (adrenodoxin), J. Biol. Chem. 247, 4476-4479 (1972). 

In summary, if the good combination of donor-acceptor subunits can be found so that the charge-separated state does not lie substantially higher than the locally excited states and if the polar solvent is adequately chosen to lower the energy of the charge-separated state, TICT state will be responsible for the anomalous fluorescence emission. 

C. Some Extended Donor-Acceptor Systems with Anomalous Fluorescence... 

D. Donor-Acceptor Systems without Anomalous Fluorescence Band... 

It is important to have an idea how widespread the relaxation mechanisms discussed previously are present in chemistry and biology. In a recent review article2 many more compounds that emit an additional, anomalous TICT fluorescence have been presented, ranging from a variety of naphthalene and anthracene derivatives to biologically important compounds like indoles and purine derivatives. The question remains whether other systems which do not show the anomalous fluorescence band might nevertheless be understood on the same basis. It may be the case that either the two fluorescence bands are superimposed or that the product fluorescence has not yet been observed because of quenching processes or because of a red shift into the infrared region. 

The first systems without anomalous fluorescence discussed in the context of TICT states were coumarine laser dyes. Jones and coworkers208210 demonstrated that dialkylaminocoumarines like 7C showed an increase of the nonradiative decay rate in strongly polar solvents. This effect is dramatically increased if the acceptor properties of the coumarine skeleton are stronger, for example, in F7C. On the other... 

Cao H, Diaz DI, DiCesare N, Lakowicz JR, Heagy MD. Monoboronic acid sensor that displays anomalous fluorescence sensitivity to glucose. Organic Letters 2002, 4, 1503-1505. 

In compiling the information in this chapter, I have relied heavily on several very comprehensive reviews that have appeared over the past few years [1-7]. In particular, the 1978 review by T irro et al. [1] is extremely thorough in describing the intra- and intermolecular photophysics and chemistry of upper singlet and triplet states. In fact, rather than reproduce the same details here, I direct the reader to this review for a summary of upper state behavior reported prior to 1978. (A description of azulene and thione anomalous fluorescence is included since these systems are the best-known systems that display upper state behavior.) I also direct readers to the reviews by Johnston and Scaiano [2] and Wilson and Schnapp [3] which focus on the chemistry of both upper triplet states and excited reaction intermediates as studied by laser flash photolysis (one- and two-color methods) and laser jet techniques. Also, Johnston s thorough treatment of excited radicals and biradicals [4] and the review of thioketone photophysics and chemistry by Maciejewski and Steer [5] are excellent sources of detailed information. 

The best-known exception to Kasha s rule is the anomalous fluorescence displayed by azulene and its derivatives (nonaltemant hydrocarbons) and some aliphatic and aromatic thioketones. 

The well known anomalous fluorescence from S2 has been interpreted in terms of a much slower radiationless transition out of S2 than Si, such that for Si the fluorescence lifetime is severely shortened relative to the radiative lifetime. The anomaly is related to the unusual energy disposition of the two lowest excited singlet states. Hochstrasser and Li wished to ascertain whether the spectral linewidths were consistent with this interpretation and also whether the Si linewidths of azulene-ds were narrowed in comparison, as theoretically predicted. Their results are listed in Table 1. The spectral resolution was claimed to be <0.15 cm-1 as linewidths in the S2 system corresponding to the observed fluorescence lifetime are of the order of 10-4 cm-1, the linewidths of 0.50 cm-1 measured must be considered crystal-imposed. It is assumed that the maximum crystal inhomogeneity contribution to the Si linewidth is similarly 0.50 cm-1. This leads to a line broadening due to rapid nonradiative electronic relaxation of 1.61 (-hs) and 1.27 (-da) cm-1 as compared to 0.64 cm-1 (-hs) determined by Rentzepis 50> from lifetime studies of azulene in benzene solution at 300 K. 

Unfortunately, many of these mechanisms have been claimed to be the only source of the dual fluorescence. From today s viewpoint, it can be said that all these mechanisms are active, for one or the other specific case, and that even more general combinations of TICT with other photoreactions can occur (Sect. 7), but none of these mechanisms alone can explain the anomalous fluorescence observed. A consistent picture is obtained, however, when the TICT model is used and the other mechanisms are treated as additional factors which are sometimes present, sometimes absent. 

Recently Zachariasse and coworkers have questioned the role of TICT in DMABN and related molecules [180-183]. They observed an absence of a linear correlation between the energy of the anomalous fluorescence band and the redox potential of the donor and acceptor groups and also observed dual emission in... 

In Figure 5.18 the absorption and emission spectra of azulene are shown. The anomalous fluorescence of azulene from the S, state is easy to recognize. The AP(F) spectrum exhibits a deep minimum at 33,900 cm. The small peak in the absorption spectrum at the same wave number is therefore not due to vibrational structure but rather to another electronic transition, the polarization of which had been predicted by PPP calculations. Figure 5.19 shows all four types of polarization spectra of phenanthrene. FP becomes negative at the vibrational maxima of the fluorescence the most intense vibration is not totally symmetric, in contrast to the one which shows up weakly. For all absorption bands, AP(P) = -0.3. The polarization direction of phosphorescence is perpendicular to the transition moments of all transitions lying in the mo-... 

SA, too, shows anomalous fluorescence (1,2), but a straightforward interpretation is not possible in this case. The long wavelength absorption maximum is close to that of the MSA (Table 2), and a fluorescence with a maximum at 22,100 cm (CH3OH) has been reported by Weller (1,2). Recent experiments of our group have shown that this fluorescence depends critically on the concentration of SA (25). The emission maximum in methanol is shifted from 22,700 (10-2m) to 22,900 (10 3), 24,600 (10 ) and 24,800 (<10 5 M). Although a very small dissociation constant of the carboxylic group of SA in methanol (pK = 7.9 (25), compared to pK = 3 in water) has been reported, the concentration dependence is due to dissociation into salicylate ions. This is evidenced by measurements of the decay times and quantum efficiencies (25). 

The proposed mechanism of the anomalous fluorescence of this acid consists in the formation of the hydrogen-bonded complex, followed by absorption of a photon and intramolecular proton... 

Hydroxy-l-naphthoic acid does not show anomalous fluorescence shifts, nor does 2-hydroxy-l-naphthoic acid. 

Some pseudoazulene systems show weak fluorescence (measured for 26, 27, 33, 39, 40, 44, 56, and 68)." 2 With the exception of pseudoazulenes 68 and 56, the emission by the other systems is due to the transition S2- So. Thus, with respect to fluorescence spectra, many pseudoazulenes show essentially the same properties as azulenes. The quantum yields of fluorescence are very low (between 10 and 10 ), They are markedly dependent upon the energy gap (S1-S2) and the flexibility of the pseudoazulene systems. The fluorescence quantum yields increase when additional benzene rings are introduced onto the uncondensed ring skeletons of the pseudoazulene systems, A slight increase in quantum yields is also observed if halides or phenyl groups are introduced. To explain this anomalous fluorescence the energy-gap model and a quantum chemical model have been invoked however, neither could explain all effects, Hitherto, no other luminescence spectra (particularly Sj Sq fluorescence and phosphorescence) have been observed for pseudoazulenes... 

Many linear polyenes exhibit anomalous fluorescence behaviour in the sense that the fluorescence rate constant kf calculated from the absorption spectrum (Equation 2.11) is much smaller than that determined by lifetime and quantum yield measurements (Equation 3.33). In 1972, Hudson and Kohler reported high-resolution absorption and emission spectra of all-trart.v-l, 8-diphenylocta-l, 3,5,7-tetraene at low temperature, which proved that the lowest excited singlet state Si was not that reached by the strongly allowed 7t,Jt transition (/ 1.5) that is predicted by MO theory and observed at 410nm.3" Rather, very weak (f 0.06), structured absorption that had been hidden under the tail of the jt,jt -absorption in solution spectra was detected at slightly longer wavelengths. 

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