The invention concerns compounds of formula (I ou II), or their salts, in which the radicals have for instance the following meaning: R1 and R2 are each hydrogen, C1-C8 alkyl, cyano or -NO2 or together are (-CF2-)m, -CF(OCH3)-CF2-CF(OCH3)-, -CF[NH2]-CF2-CF[-NH2]-, -C(=O)-O-C(=O)-, -C(=NH)-NH-C(=NH)- or -C(=O)-NH-C(=O)-; R3 and R4 are methyl; A1 and A2, independently of each other, are formyl, an acetal or thioacetal radical, phenyl, pyridiniumyl, pyridyl or other heterocyclic groups, or groups of formula (III or IV); X1 and X2 are S, O or N(R18); Y1 and Y2 are =CH- or =N-; R5 and R6 are hydrogen, halogen, -B(OH)2, C1-C8 alkyl, C1-C8 alkylthio, cyano, nitro, -N(R17)2, -C(=O)-R19, -C≡CH, phenyl or pyridyl, and R9 is a bridging group containing up to three hetero-atoms. The invention also concerns the preparation of these compounds for example by reacting alkenes with 3-haloheterocycles in the presence of a strong base; intermediates of formula (VIb) used to produce these compounds, where A2, R4, X2 and Y2 are as above, where A2 cannot be -CHO, but additionally -B(OH)2 and -CH=NR26; compositions containing these compounds, and the use of the compounds or compositions described above as dyes, colour indicators, photo-switches or data stores.