Photochemistry of the pi-extended 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene system: Generation and characterisation of the radical cation, dication, and derived products

Flash photolysis of bis[4,5-di(methylsulfanyl)1,3-dithiol-2-ylidene]-9,10-d ihydroanthracene (1) in chloroform leads to formation of the transient radi cal cation species 1(.+) which has a diagnostic broad absorption band at la mbda (max) approximate to 650 nm. This band decays to half its original int ensity over a period of about 80 mus. Species 1(.+) has also been character ised by resonance Raman spectroscopy. In degassed solution 1(.+) disproport ionates to give the dication 1(2+) whereas in aerated solutions the photode gradation product is the 10-[4,5-di-(methylsulfanyl)1,3-dithiol-2-ylidene]a nthracene-9(10H)one (2). The dication 1(2+) has been characterised by a spe ctroelectrochemical study [lambda (max) (CH2Cl2) = 377, 392, 419, 479 nm] a nd by an X-ray crystal structure of the salt 1(2+)(ClO4-)(2), which was obt ained by electrocrystallisation. The planar anthracene and 1,3-dithiolium r ings in the dication form a dihedral angle of 77.2 degrees; this conformati on is strikingly different from the saddle-shaped structure of neutral 1 re ported previously.