Also well suited as guest dyestuffs in the scope of the present invention are those compounds in which one of R1, R2, R3 and R4 is a group of the partial formulae (IId) or (IIe) and a second one is 4-alkylphenyl (IIa), 4-alkoxyphenyl (IIb) or 4-alkylcyclohexyl (IIc); this second cyclic radical is preferably in the peri-position with respect to the first one, i.e., the two cyclic radicals are place