Fluorene spectra

The excited triplet states of quinones can be fairly readily populated by irradiation and nuclear polarization observed (Cocivera, 1968). Hydrogen atom abstraction leads to the relatively stable semiquinone radicals and, in alkaline media, radical anions. Recombination of radical pairs formed in this way can give rise to CIDNP signals, as found on irradiation of phenanthraquinone (20) in the presence of donors such as fluorene, xanthene and diphenylmethane (Maruyama et al., 1971a, c Shindo et al., 1971 see also Maruyama et al., 1972). The adducts are believed to have the 1,2-structure (21) with the methine proton appearing in absorption in the polarized spectrum, as expected for a triplet precursor. Consistently, thermal decomposition of 21 as shown in equation (61) leads to polarization of the reactant but now in emission (Maruyama... 

The relative amounts of 9-phenyl-9-fluorenol and 9-bromo-9-phenyl-fluorene were determined as follows A 13C NMR spectrum (CDCI3 solution, Bruker 400 MHz) of an authentic sample of 9-bromo-9-phenylfluorene was recorded and then doped in 1% increments with authentic 9-phenyl-9-fluorenol. A 13C NMR spectrum (CDCI3 solution, Bruker 400 MHz) was recorded after each doping, and the heights of the peaks at 120.3 ppm (bromide) and 120.0 ppm (alcohol) were monitored. These spectra were compared with a 13C NMR spectrum (CDCI3 solution, Bruker 400 MHz) of the sample in question. Application of this technique to an evaporated aliquot of the reaction mixture in Step B, indicated >97% conversion of alcohol to bromide after 24 hr. 

The color of fluorene copolymers can also be shifted into the UV, as exemplified by copolymer 335 [413]. Its PL spectrum in THF solution is blue-shifted by 49 nm compared to... 

One case of n—5 —n delocalization was demonstrated by Stevenson et al. (2006). The potassinm anion-radical salt of l-(9-methyl-9H-fluoren-9-yl)-4-methyl benzyl is characterized by the delocalization of an nnpaired electron within the fluorenyl moiety only. Its ESR spectrnm completely coincides with the spectrnm of the potassium anion-radical salt of the 9,9-dimethyl fluorene anion-radical in THE However, the cesium anion-radical salt of the fluorenyl methylbenzyl derivative produces the ESR spectrum corresponding to the placement of this cation between the fluorenyl and methylbenzyl moiety. The conditions of n—s—n delocalization appear An unpaired electron spends its time within both fluorenyl and methylbenzyl fragments. The situation is explained in Scheme 3.54. 

Dibenzothiophene acts as a 7r-electron donor and readily forms complexes with known electron acceptors. In such cases the electronic spectrum of a solution of the two compounds shows a new absorption band, usually in the visible region. The order of donor strengths of several o,o -bridged biphenyls has been estimated from their respective charge-transfer spectra and found to be carbazole > fluorene > dibenzothiophene >dibenzofuran. Dibenzothiophene forms complexes with tetracy-anoethylene, various polynitro derivatives of fluorenone, > naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, and tetra-methylmic acid. ... 

Oxidation of fluorene (C13H10) with chromic acid gives fluorenone (CnHgO). If the reaction does not go to completion, then a mixture of the starting material and the product is usually obtained. The H NMR spectrum below is from a partially oxidized sample of fluorene so it contains a mixture of fluorene and fluorenone. Determine the relative amounts (mole %) of fluorene and fluorenone in the mixture. 

Steadily in the order 359, 385, 395, and 402 nm. The emission spectra exhibit a clearer vibrational fine structure than the absorption spectra. For spiro-sexiphe-nyl, 35b, a detailed analysis shows that the vibrational splitting of 0.20 eV corresponds to a phenyl breathing mode in the Raman spectrum [108]. If for spiro-sexiphenyl the outer biphenyl moieties are fixed parallel as in 4-Spiro (43), the absorption maximum is shifted from 346 to 353 nm (amorphous films) and the fluorescence maximum from 420 to 429 nm, maintaining the Stokes shift. The corresponding spectra are shown in Figure 3.17. The absorption signal at 310 nm in the spectrum of 43 can be attributed to the terminal fluorene moieties. The quantum yields for the fluorescence in the amorphous film are 38% for 35b and as high as 70 10% for 43 [89]. 

Loss of ethylene and subsequent formation of the stable 3//-pyrrolinine cation dominates the mass spectrum of 2,3,4,5-tetrahydro-l//-l-benzazepine <75OMS(10)992). Biphenylene (m/e 152), acridinium cation (m/e 179) and fluorene cation (m/e 165) are the major fragments in the mass spectra of dibenz[T>,/]azepines (74CJRV101). 

Hutchison reported the first ESR spectrum of a metastable phosphorescent state by study of naphthalene oriented in durene crystals.4 Since then, similar spectra have been recorded for several other polynuclear aromatics both oriented in host crystals and randomly suspended in glassy matrices. D values for all these ir,n excited states are quite low, indicating little interaction between the unpaired electrons. Interestingly, D for the quinolines equals 0.10cm"1 just as in naphthalene,197 indicating that the presence of a heteroatom does not necessarily change the ir,w nature of the lowest triplet state very much. A similar conclusion has been reached from a comparison of the ESR spectra of fluorene, carbazole, dibenzofuran, and dibenzothiophene.198... 

We now consider hydrogen transfer reactions between the excited impurity molecules and the neighboring host molecules in crystals. Prass et al. [1988, 1989] and Steidl et al. [1988] studied the abstraction of an hydrogen atom from fluorene by an impurity acridine molecule in its lowest triplet state. The fluorene molecule is oriented in a favorable position for the transfer (Figure 6.18). The radical pair thus formed is deactivated by the reverse transition. H atom abstraction by acridine molecules competes with the radiative deactivation (phosphorescence) of the 3T state, and the temperature dependence of transfer rate constant is inferred from the kinetic measurements in the range 33-143 K. Below 72 K, k(T) is described by Eq. (2.30) with n = 1, while at T>70K the Arrhenius law holds with the apparent activation energy of 0.33 kcal/mol (120 cm-1). The value of a corresponds to the thermal excitation of the symmetric vibration that is observed in the Raman spectrum of the host crystal. The shift in its frequency after deuteration shows that this is a libration i.e., the tunneling is enhanced by hindered molecular rotation in crystal. 

Figure 1. FTMS NICI spectrum of a mixture of fluorene [(M+14) at m/z 180], fluoranthene [M- at m/z 202)], and benzo(a)pyrene [(M at m/z 252)]. Methane was used as the reagent gas at a static pressure of 7 x 10 6 torr.

Figure 2. FTMS NICI spectrum of a mixture of fluorene and 9-methyl fluorene, using argon as the reagent gas. Observed anions at 180.058 and 180.094 correspond to C H 0 and C H O , respectively. (Reproduced with permission from ref. 18. Copyright 198 7 Valley.)...

Figure 3. FTMS NICI spectrum of 9,9-d2 fluorene using 1802 as a reagent gas (1 x 10"5 torr) and a 200 msec electron beam.

The nature of the DNA adduct remains to be determined. However the spectrum of the isolated DNA is similar to that of the DNA adduct formed when 2-aminodifluorenylamine is oxidized by a peroxidase-H202 reaction mixture. Furthermore a similar DNA adduct is formed when DNA is added at a time when the blue imino derivative is maximal. Furthermore in the presence of DNA much less extractable azofluorene, aminodif luoreny lamine or polymer was formed suggesting that DNA reacts with the amino-fluorene cation radical and 2-iminodifluorenylamine. 

Onychine (135) was first described as a natural product in 1976, when its isolation from Onychopetalum amazonicum (Annonaceae) was reported (83), and its structure was given as 4-methyl-l-azafluoren-9-one (158) on the basis of elemental analysis and high-resolution MS, as well as UV, IR, and H-NMR spectra. As in all the azafluorenone alkaloids discovered to date, the complex UV spectrum is reminiscent of that of fluoren-9-one, and the H-NMR spectrum clearly indicates the presence of a 2,3-disubstituted 4-methylpyridine moiety. The immediate conclusion, therefore, is that onychine is either l-methyl-4-azafluoren-9-one (135) or 4-methyl-l-azafluoren-9-one (158), which is supported by the spectral properties of the secondary alcohol obtained by reduction of the ketone group and of the acetylation and hydrogenolysis products of this... 

Figure 2. Fluorescence spectrum in a nitrogen matrix at 15 K (excited by a 2.5-kW mercury-xenon lamp) of an adsorption chromatography fraction from a coking plant water sample. Compounds BbF, benzo[b]fluorene C, chrysene BeP, ben-zo[e]pyrene P, pyrene BkF, benzo[k]fluoranthene BaP, benzo[a]pyrene U, unknown ( ).

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