The invention relates to compounds of formula I ##STR1## wherein R.sup.1 is C.sub.12 -C.sub.30 alkyl, R.sup.2 is hydrogen or C.sub.1 -C.sub.30 alkyl, R.sup.3 is C.sub.1 -C.sub.3 -alkyl or C.sub.1 -C.sub.3 alkoxy, R.sup.4 may have one of the meanings of R.sup.3 or is halogen, k and n are each independently of the other 0, 1 or 2, and R.sup.5 and R.sup.6 are each independently of the other C.sub.1 -C.sub.4 alkyl, any of which alkyl groups as defined herein may also be partly fluorinated or perfluorinated, with the proviso that R.sup.1 is alkyl of not less than 18 carbon atoms if R.sup.2 is hydrogen or alkyl of less than 12 carbon atoms.From these compounds it is possible to prepare molecular aggregates, especially LB layer systems, which have reversible thermochromic and solvatochromic properties. The invention also relates to intermediates of formula II ##STR2## wherein R.sup.1, R.sup.2, R.sup.3 and n are as defined above.