Bianthrone

The photochemistry of unsaturated nitro compounds has been investigated by Chapman and co-workers.<63) Photolysis of 9-nitro-anthracene in degassed solutions leads to anthraquinone and 10,10 -bianthrone ... 

The bianthrone analogue 18 crystallizes as yellow plates from 1,2-dichloroethane (m.p. 351-357 °C (decomp.)) and as deep violet needles (m.p. 110-112 °C (decomp.)) from dichloromethane or as deep violet cubes (m.p. 84-86 °C (decomp.)) from benzonitrile solution <1997AGE2495>. 

Bianthrone and thianthrene also dissolve in aluminium chloride and ether to give red solutions exhibiting paramagnetic resonance. 

The discovery of diradicals in sulfuric acid or Lewis acid solutions of bianthrone and thianthrene raises the possibility of acid-catalyzed radical reactions for any unsaturated compound.448 Anything that increases the equilibrium concentration of the diradical should promote radical reactions. These results are important because previous to their discovery few chemists would have hesitated to say that a reaction catalyzed by sulfuric acid or aluminum trichloride, for example, was an entirely ionic one. Now we would not want to venture such an opinion without other reasons. 

FIGURE 2.41. a Reductive cyclic voltammetry of bianthrone in DMF + 0.1 Mn-Bu4NC104 at 21°C. Scan rate, 10 V/s. b Two conformations of bianthrone. c Reduction and oxidation pathways. Adapted from Figure 11 in reference 44, with permission from Routledge/Taylor and Frances Group, LLC. 

Table 8. 4a,4b-Dihydrophenanthrenes with 7 conjugated rings, derived from bianthrones...

Stereoisomerism in molecules interchange between stereoisomers that have different colours, e.g. bianthrones... 

Figure 1.17 Thermochromic bianthrones folded A-form and twisted B-form.

Photochromic or phototropic dye stuffs are used as the basis of photochemical high speed memory with an erasable image. They can also be used as automatic variable density filters for example as Q-switches in high intensity lasers. For thermochromic substances colour change is observed on change of temperature (spirans, bianthrones). 

In several types of compounds, excited triplet levels lie very close to the ground states, as has been mentioned already. Such thermal population of low-lying triplet levels occurs frequently in inorganic complexes as well as with organic biradicals. Thermochromism of bianthrone has been explained as due to thermal conversion to a triplet state.129... 

Bianthrone and Analogous Compounds. Bianthrone (VI) and a number of substituted and related compounds (e.g. xanthylidinean-throne, VII) are photochromic at low temperatures. However, Hirsh-... 

Electron paramagnetic resonance (EPR) studies on pyridine solutions of bianthrone by Wasserman (41) suggest that the thermochromic form may have one unpaired electron localized on each half of the molecule. The structure proposed by Woodward and Wasserman (42) is VIII which they consider to be identical to the colored photochromic form. Klochkov (43) has warned that free radicals may be involved in decomposition processes occuring at high temperatures in studies of the bian-... 

In bianthrones (15a) the B form is thermally and photochemically83 accessible, and both the B — A barrier (AH ) and AH0 could be determined by monitoring the equilibrium and the reaction rate as functions of the temperature79. The B - A barrier was found to... 

FIGURE 5. Schematic potential energy curve and exchange pathways for a 2,2 -substituted bianthrone... 

The changes in the bianthrones and bixanthylidenes can be followed photometrically, since the visible absorption occurs at much longer wavelength (600-650 nm) in the B form than in the A form ( 400 nm)83. The A —> B transition is favoured by high pressure on the crystal (triboluminescence) or in solution84. 

Hirshberg, Y. Photochromie dans la Serie de la Bianthrone. Compt. rend. 231, 903 (1950). 

Two related fused-ring systems, 10,l0 -dimethyl-9,9 -biacridylidene dication [1] and bianthrone [2] represent extreme cases in electron-transfer... 

The reduction of bianthrone [2] follows a similar pathway (Hammerich and Parker, 1981a Olsen and Evans, 1981). The kinetics of the conformation... 

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