Stokes shift conjugates

These spectra show uniformly three resolved vibrational components, the second component being always the strongest. The vibrational spacings fall in the range 1600—1200 cm, usual values for C—C stretching modes of conjugated polyenes. The Stokes shifts of 44 and 46 are notably small especially when compared to those of the cis-1,2-diarylethylenes ... 

The fluorescence properties of 2,2-diaryl-substituted l-(9-anthryl)-ethylenes 87c-e differ markedly from those of 87a, b by a decrease in the quantum yields of emission, and by the loss of vibrational fine structure of the emission spectra, which is associated with a dramatic increase of the Stokes shifts. For the 2,2-diphenyl derivative 87c in cyclohexane solution, the quantum yield is 0.29, and the Stokes shift is 5600cm-1. For 9-anthryl-ethylene 87e, in which the formal conjugation has been extended by a terminal methylene group, the quantum yield in cyclohexane is as low as... 

The electronic effect of perfluoroalkyl substituents on the absorption spectra of arenes is relatively small (e.g., Xmax 3-perfluorooctylthiophe-ne = 229 nm 3-octylthiophene = 235 nm). Thus, the anomalously low absorption maximum of 504 is the effect of twisting around the backbone. It is apparent that the difference in size of the side chains is sufficiently large to cause twisting of the conjugated backbone of 504 due to steric interactions between the perfluoroalkyl substituents and the adjacent repeat unit. 504 exhibits green fluorescence (Xmax = 512 nm) in solution with a maximum blue shifted by 58 nm relative to POT (570 nm). Accordingly, 504 shows a Stokes shift of ca. 1.4 eV (186 nm) compared to only 0.6 eV (126 nm) for POT. 

Absorption bands of tetraaryldisilenes appear at a little longer wavelength than those of tetraalkyldisilenes. Leites et al. have found that the absorption and fluorescence spectra of tetramesityldisilene 1 depend on the forms of crystals, suggesting dependence of the conjugation between aryl n and Si = Si ti systems on the rotational conformations around Cm- Si bond.78 While both a 3-methylpentane solution of 1 and a thin film of 1 show the n-m absorption maxima at around 420 nm, crystals of unsolvated 1 exhibit the band at 465 nm. Unsolvated solids and a thin film of 1 show broad fluorescence bands at about 560 and 515 nm, respectively large Stokes shifts indicate a substantial geometry change upon excitation. 

Conjugation of fluorescein to an antibody reduces its quantum yield by half (from 0.85 to 0.5-0.3) (2). Nonetheless, conjugated fluorescein provides good fluorescence intensity, and its small size and hydrophilic nature are advantageous. Drawbacks include a short Stokes shift and a... 

A number of derivatives of fluorescein have been synthesized. Dichlo-rotriazinylamino fluorescein (DTAF) (1) is spectrally identical to FITC, but provides a more consistent and stable antibody conjugate. Succinimidyl esters of fluorescein are also available for conjugation to antibodies. BODIPY FL2 (Molecular Probes, Inc., Eugene, OR) has been offered as a substitute for fluorescein. It has a short Stokes shift, but offers higher fluorescence intensity, and is claimed to be more photostabile and less pH-sensitive than fluorescein. 

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