Electrochromic device having improved light stability

An electrochromic device comprising

• (a) a pair of glass or plastic plates or plastic films wherein at least one such plate or film is provided on one side each with an electrically conductive coating, wherein
• (1) at least one such plate or film and its conductive coating is transparent,
• (2) the other such plate or film and its conductive coating is optionally mirrored,
• (3) the electrically conductive layer of one or both of the two plates or films is optionally divided into separate segments optionally provided with individual contacts, and
• (4) the plates or films are joined on the sides of their conductive coating by means of a sealing ring to form a volume;
• and
• (b) the volume formed by the two plates or films and the sealing ring is filled with an electrochromic medium comprising a pair of electrochromic substances OX2 and RED1, wherein
• (1) OX2 is a reducible electrochromic substance, and
• (2) RED1 is an oxidizable electrochromic substance represented by at least one of the formulas
• wherein
• R201 is aryl,
• R202 is alkyl, cycloalkyl, alkenyl, aralkyl, or aryl,
• B is a bivalent bridge,
• m and n, independently of one another, are integers from 1 to 4, and
• R203 to R206, independently of one another, are hydrogen, halogen, alkyl, alkoxy, cyano or aryl,
• with the provisos that when m is at least 2, two adjacent R203 together also optionally represent a bivalent —CH═CH—CH═CH— radical and when n is at least 2, two adjacent R204 together also optionally represent a bivalent —CH═CH—CH═CH— radical.