Asymmetric stilbene compounds

An asymmetric UV absorbing compound having the formula:

• ##STR29## in which M is hydrogen, an alkali metal atom, calcium, magnesium, ammonium or a cation formed from an amine;
• Xa and Xb are the same or different and each is NH.sub.2 ;
• NH(C.sub.1 -C.sub.4 alkyl);
• N(C.sub.1 -C.sub.4 alkyl).sub.2 ;
• NH(C.sub.2 -C.sub.4 alkoxyalkyl);
• N(CH.sub.2 CH.sub.2 OH).sub.2 ;
• a group NH--Z--NR.sub.1 R.sub.2 in which Z is C.sub.2 -C.sub.14 alkylene or optionally substituted arylene, and R.sub.1 and R.sub.2 are the same or different and each is C.sub.1 -C.sub.12 alkyl or R.sub.1 and R.sub.2, together with the nitrogen atom to which they are each attached, form a morpholino, piperidino or piperazino ring;
• or is an aminoacid residue;
• C.sub.1 -C.sub.4 alkoxy;
• or hydroxy-substituted-C.sub.2 -C.sub.4 alkoxy;
• and Ya and Yb are the same or different and each is a substituted amino group having both UVA and UVB-absorbing properties, and provided that one of Xa and Xb is different from the other and/or one of Ya and Yb is different from the other, whereby Ya and Yb each is a group having the formula:
• ##STR30## in which R.sub.3 is CN;
• SO.sub.2 R.sub.5 in which R.sub.5 is C.sub.1 -C.sub.12 alkyl, C.sub.1 -C.sub.12 alkoxy, NH.sub.2, NH(C.sub.1 -C.sub.4 alkyl), N(C.sub.1 -C.sub.4 alkyl).sub.2, N(CH.sub.2 CH.sub.2 OH).sub.2, C.sub.1 -C.sub.4 alkoxy-substituted-C.sub.2 -C.sub.4 alkoxy or hydroxy-substituted-C.sub.2 -C.sub.4 alkoxy;
• COR.sub.5 which R.sub.5 has its previous definition;
• COOM in which M has its previous definition or NHCOR.sub.5 in which R.sub.5 has its previous definition and in which R.sub.4 has the same definition as R.sub.3 or is H, OH, C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.4 alkoxy, with the proviso that when R.sub.3 is COOM, Ya and Yb are different.