Anthraquinone, absorption spectra

Figure 7.42 shows the change in the absorption spectrum of this actinometer during the course of irradiation. One minor complication in its use is the necessity to deoxygenate the solution. In the presence of oxygen the dihydroxyanthracene reverts to anthraquinone so that the solution can be reused after deoxygenation. 

The quantum yield of the primary hydrogen abstraction process is unity, and is independent of irradiation wavelength, light intensity and temperature. Its wavelength range follows of course the absorption spectrum of anthraquinone so that this actinometer is particularly well suited for the UV region. 

Figure 7.5. Absorption spectra of l-(l-naphthoxy)-anthraquinone in benzene (C = 2 x 10 4 mol/liter) (1, 2),32 l-phenoxy-4-methoxyanthraquinone in benzene (C = 1 x 10 4 mol/liter) (3, 4) 9 and 1-phenoxy-4-aminoanlhraquinone (5-7)15 before (1, 3, 5) and after (2, 4, 6) UV irradiation as well as absorption spectrum of the ana form for l-phenoxy-4-aminoanthraquinone (7).

The photolysis of non-photochromic l-acetoxy-9,10-anthraquinone in alcohols resulted in a photochemical reaction of hydrogen atom removal from solvent.21 This reaction is typical for 9,10-anthraquinones. The absorption spectmm that was observed after a flash pulse was similar to the absorption spectrum of the anthrasemiquinone radical. The lifetime of this radical depended on the oxygen concentration in solution. 

A more remarkable elongation of the CS lifetime was attained by complex formation of yttrium triflate [Y(OTf)3] with the CS state in photoinduced ET of a ferrocene-anthraquinone (Ec AQ) dyad (53). Photoexcitation of the AQ moiety in Ec AQ in deaerated PhCN with femtosecond (150 fs width) laser light results in appearance of the absorption bands 420 and 600 run at 500 fs, as shown in Eig. 14(a) (53). The absorption bands 420 and 600 nm, which are assigned to AQ by comparison with the absorption spectrum of AQ produced by the chemical reduction of AQ with naphthalene radical anion (53). The decay process obeys first-order kinetics with the lifetime of 12 ps [Eig. um. 

Orthorhombic needles from benzene + petr ether, mp 155. Absorption spectrum Martin, Ann. Combustibles Lit. 12, 967 (1937). Sol in most organic solvents without fluorescence. Any fluorescence present is due to anthrano). Tendency to change to anthraquinone. Equilibrium in abs ale 89% anthrone ] 1% anthrano]. 

Ultraviolet and visible light (UV-VIS) analysis is the most used identification technique for anthraquinones. The UV-VIS absorption spectrum of an anthraquinone is a combination of the absorptions arising from partial acetophenone- and benzoquinone chromophores (Fig. (7)) [1,20,62]. 

Anthraquinones, having no 1-hydroxylgroup show only one carbonyl peak and its position is a little shifted to lower wave numbers by substitutions at C-2 or C-3. The absorption bond of the hydroxy stretch frequency occurs at 3320-3380 cm"1 [62], The IR spectrum of alizarin in KBr is depicted in Fig. (9). 

When sublimed, anthraquinone forms a pale yellow, crystalline material, needle-like in shape. Unlike anthracene, it exhibits no fluorescence. It melts at 286 0 and boils at 379 —38UC. At much higher temperatures, decomposition occurs. Anthraquinone has only a slight solubility in alcohol or benzene and is best recrystaUized from glacial acetic acid or high boiling solvents such as nitrobenzene or dichlorobenzene. It is very soluble in concentrated sulfuric acid. In methanol, uv absorptions of anthraquinone are at 250 nm (e = 4.98), 270 nm (4.5), and 325 nm (4.02) (4). In the ir spectrum, the double alljdic ketone absorbs at 5.95 am (1681 cm ), and the aromatic double bond absorbs at 6.25 im (1600 cm ) and 6.30 Jm (1587 cm ). 

The excellent photostability of the anthraquinone dyestuffs are related to the introduction of a proton donor in the a-posi-tion of the anthraquinone molecule [58], The anthraquinone molecule itself has no absorption band in the visible spectrum [46], so at least one of the 1,4, 5, or 8 (or 2,... 

The IR spectrum of an anthraquinone gives information on the environment of the carbonyl groups in the 9- and 10-positions. If a peri hydroxyl group is present, the carbonyl absorption band will show a shift to smaller wave numbers due to hydrogen bonding between the peri hydroxyl and the adjacent carbonyl group (120). The presence... 

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