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Excimers, chirality

New absorption shoulders appear strongly at 250 and 345 nm. Given this evidence of ground-state interaction, the fluorescence band of the noneclipsed naphthalenophanes should be red-shifted below the peak emission of the dimethylnaphthalene solution excimer. In fact, the emission of chiral [2.2](2,6) naphthalenophane is blue-shifted 900 cm 1, and the emissions of the onh -[2.2](l,4), onfi-[3.3](l,4), and chiral [2.2](1,5)... [Pg.52]

A chiral triether (syn-syn) with two different ether residues (Y1 = CH2C02Et Y2 = CH2C02CH2-pyrene, type AABH) has been obtained (55%) by direct alkylation of the corresponding monoether (K2C03/THF),120 and resolved by enantioselective HPLC (Chiracel OD). The excimer fluorescence of 58 increased up to twofold by addition of e.g. L-alanine methyl ester or L-phenylglycinol but no chiral discrimination was observed. [Pg.167]

Haenel et al. investigated [3.3]naphthalenophanes as model systems for excimers [78]. Pyrolysis of the sulfone 257 possessing two 2,6-disubstituted naphthalene units led to a 3 2 mixture of diastereomers consisting of the achiral phane 259 with mirror-symmetry and of a slightly crossed, chiral phane 258. A mixture of a slightly crossed and a clearly crossed phane 261 and 262, respectively, was obtained after pyrolysis of the (2,6)(l,5)sulfone 260. Pyrolysis of 263 containing two 1,4-disubstituted naphthalene units resulted in a 3 2synjantimixture of 264 and 265 [79]. The absorption spectra of the syn and anti isomers show more differences than in the case of the comparable [3.3] or even [2.2]phanes. [Pg.101]

Another example of intramolecular CT complex formation is provided by trans-4-dimethvlamino-4 -(1-oxobutvl)stilbene Solvent effects on the spectrum give a value of 22D for the excited state dipole moment. The effect of electric field on the fluorescence of 4-(9-anthry1)-N.N.-2.3,5,G-hexamethy1-aniline shows this compound forms an excited state whose dipole moment does not change with solvent . Chiral discrimination in exciplex formation between 1-dipyrenylamine and chiral amines is very weak . In the probe molecule PRODAN (6-propionyl)-2-(dimethylamino)—naphthalene the initially formed excited state converts to a lower CT state as directly evidenced by time-resolved spectra in n-butanol. Rate constants for intramolecular electron transfer have been measured in both singlet and triplet states of covalently porphyrin-amide-quinone molecules . Intramolecular excimer formation occurs during the lifetime of the excited state of bis-(naphthalene)hydrazides which are used as photochemical deactivators of metals in polyethylene . ... [Pg.17]

Several chiral substituted a-phenyl-alkyl alcohols, which were partially enantio-merically enriched, were successfully purified by this method after esterification with 9-anthroic acid optical purities higher than 95% were obtained.Fluorescence studies of racemic compounds show a characteristic a-type excimer emission, whereas the chiral enantiomer exhibits a typical y-type monomer emission. Figure 7 shows the spectra of l-(2-chlorophenyl)ethyl 9-anthroate for a crystalline sample of enantiomeric (1) and racemic (2) at 77 K. It has been demonstrated that in the absence of configurational disorder chiral impurities in the range of 1 % can be detected by this method. ... [Pg.218]

The excimer of poly(2-napAla) showed an intense circular polarization, indicating that the excimer has a skewed chiral configuration. Therefore, the excimer in poly(2-napAla) may be formed not in the randomly coiled part (e.g., at the termini), where no particular excimer configuration is expected, but in the helix part of the polypeptide. Since the interchromophore distance in the helix part (6,0 A) may be too far to form an excimer, a small distortion of the side-chain and/or main-chain will be necessary to form the excimer. [Pg.345]

III. Chirality of excimers as observed with circularly polarized fluorescence spectroscopy, 203... [Pg.197]

III. CHIRALITY OF EXCIMERS AS OBSERVED WITH CIRCULARLY POLARIZED FLUORESCENCE SPECTROSCOPY... [Pg.203]

Electronic transitions of the carbazole chromophores afford a highly sensitive probe for studies of carbazole-containing polymers in respect of their absorption and emission characteristics as well as of either inherent or induced circular dichroism. They have been conveniently employed to describe microstructural characteristics of carbazole-containing polymers, including homopolymers of carbazolated a-aminoacids and of vinylated carbazoles with chiral substituents. Data obtained are entirely consistent with interpretation of polymer structures derived from related UV absorption, excimer fluorescence emission and NMR studies and are especially valuable as a completely new indication of copolymer sequence distributions. [Pg.167]


See other pages where Excimers, chirality is mentioned: [Pg.334]    [Pg.204]    [Pg.334]    [Pg.204]    [Pg.508]    [Pg.683]    [Pg.131]    [Pg.175]    [Pg.188]    [Pg.94]    [Pg.91]    [Pg.222]    [Pg.650]    [Pg.34]    [Pg.52]    [Pg.203]    [Pg.204]    [Pg.205]    [Pg.248]    [Pg.175]    [Pg.196]    [Pg.197]    [Pg.213]    [Pg.63]    [Pg.133]    [Pg.175]    [Pg.188]   
See also in sourсe #XX -- [ Pg.203 , Pg.204 ]




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