Photochromism in Dianthrone and Related Compounds. Part IV. Environmental Control of the Formation of the Two Colored Forms

Sumwzary. The kinetics of the formation of the photochromic forms B and C of tetramethyltlianthrone has been studied in triacetin and methylcyclohexane/Z-methylpentane at several temperatures. A flash spectroscopy method was developed, which allows the recording of the transicnt behaviour of the sample as function of both -wavelength and time -using a single photoflash for excitation. The results show that the photochromic forms B and C are directly populated from the excited singlet state. I n addition a new triplet-triplet absorption band in the near infrared region was detected.Introduction. -During the last two decades the reversible photochemical behaviour of the dianthrone (I) system has been the subject of many investigations. Even though many questions have been answered in the course of time there still remain unresolved aspects. Fischer gave an excellent survey with a large number of references at the 1970 IUPAC Photochemistry Symposium [l]. Our group applied the methods of flash spectroscopy t o the tetramethyldianthrone TMD (11) systems and in an earlier paper [Z] we reported

mentioning

confidence: 85%

Flash Photolysis Studies of Reversible Photoprocesses V. Photochromism and triplet states in the dianthrone system

Gschwind

Wild

1973

Photochromism in Bianthrone and Related Compounds. Part VI. The structure of the photocromic isomers of bianthrones

Korenstein

Muszkat

Fischer

1970

Self Cite

Partie experimentale. -GLndraZitds. L'acktonitrile (Fluka) a 6t6 sCch6 sur tamis mol6culaires puis distill6 sous azote sec. Le bromure de t6tra6thylammonium (Fluka) a 6t6 recristallise dans un melange ethanol-ac6tate d'6thyle. Les 6lectrolyses ont 6t6 faites, sous azote. B une cathode de rnercure s6par6e d'une anode en platine par un diaphragme poreux (Diapor). Le potentiel de la cathode Ctait fix6 par rapport au couple Ago/Ag+ (KC1 sat.) B l'aide d'un potentiostat construit dans notre laboratoire. Les polarogrammes ont 6t6 relevis avec un appareil Polarecord Metrohm E 261 R B temps de goutte contral6.PhLnylcyclopropane; Une solution de 15 g (0,054 mole) de ph6nyl-l-dibromo-l, 3-propane [5] dans 400 ml d'acdtonitrile-Et,NBr ( 0 , 3~) a 6t6 ClectrolysCe sous un courant cathodique moyen de 1 A. Le potentiel de la cathode a Ct6 tout d'abord fix6 3i -0,9 V, puis B -1,4 V en fin d'dlectrolyse afin de maintenir un courant d'intensiti convenahle. L'Blectrolyse a 6t6 interrompue lorsque le courant est tomb6 en dessous de 0,l A. On a enregistre le passage d'env. 9600 coulombs. La temp6rature a 6t6 maintenue entre 20-25" pendant la durCe de 1'6lectrolyse.Environ 250 ml d'ac6tonitrile ont Ct6 chassCs du melange final par distillation. AprBs addition de 250 ml d'eau et extraction B l'kther, 1'6vaporation des extraits 6th6r6s a abandonn6 un r6sidu qui a 6t6 distill6 sous pression r6duite. 4,3 g de ph6nylcyclopropane ont 6t6 receuillis 3i 60-61" 15 Tom sous forme d'un liquide incolore: n g = 1,5322. La structure a 6t6 confirm6e par comparaison du spectre de RMN. avec celui d'un Cchantillon authentique.Summary. The cyclic structure I11 is assigned to the C photochromic isomer of 1, S'-diniethylbianthrones on the basis of spectral and chemical evidence. Similar considerations indicate that this does not apply to the B photoisomers of bianthrones. l) 2, 3,Parts IV and V: cf. ref. [3h].

The Irreversible Photochemistry of Bianthrone

Korenstein

Muszkat

Fischer

1976

Summary. A 4a, 4b-dihydrophenanthrene-type cyclic photoisomer, the C isomer, is the major primary photoproduct of bianthrone in protic and aprotic polar solvents, and undcrgoes solventdependent secondary reactions, including the formation of tlihydrohelianthronc in protic solvents. The C isomer was shown to be formed through the singlct cxcitcd state whilc the B isomer is formcd via the triplet manifold.