These are described biphenylene compounds of formula (I) wherein R.sub.1 is a C.sub.1-C.sub.18alkyl, C.sub.2-C.sub.18alkenyl, C.sub.6-C.sub.10aryl or C.sub.6-C.sub.10aryl or C.sub.6-C.sub.10heteroaryl radical each unsubstituted or mono- or poly-substituted by hydroxy, halogen, C.sub.1-C.sub.18alkyl, C.sub.1-C.sub.18alkoxy, amino, C.sub.1-C.sub.5monoalkyamino or by di-C.sub.1-C.sub.5alkylamino; C.sub.5-C.sub.7cycloalkyl or C.sub.5-C.sub.7cycloalkenyl each unsubstituted or substituted by C.sub.1-C.sub.5alkyl; --OR'; or NR'R''; R.sub.2 is a C.sub.1-C.sub.18alkyl, C.sub.2-C.sub.18alkenyl, C.sub.6-C.sub.10aryl or C.sub.6-C.sub.10heteroaryl radical each unsubstituted or mono- poly-substituted by hydroxy, hadroxy, C.sub.1-C.sub.18alkoxy, amino, C.sub.1-C.sub.5monoalkylamino or by di-C.sub.1-C.sub.5alkylamino; --OR'; --NR'R''; or R.sub.1 and R.sub.2 together form a 5- to 7- membered monocyclic carbocyclic or heterocyclic ring; R.sub.3 is hydrogen; C.sub.1-C.sub.6alkyl or C.sub.1-C.sub.6alkoxy; R' and R'' are each independently of the other hydrogen; unsubstituted or mono- or poly-hydroxy-, halo-, C.sub.1-C.sub.18alkyl-, C.sub.1-C.sub.18alkoxy-, amino- or quaternary ammonium groupsubstituted C.sub.1-C.sub.18alkyl, C.sub.5-C.sub.7cycloalkyl or phenyl; and n is 0 or 1; wherein, when R.sub.2 is OR' or NR'R'' and n=1, R.sub.1 is not simultaneously OR'; or NR'R''. The compounds according to the invention are suitable especially as sun protection agents in cosmetic, pharmaceutical and veterinary medicine preparations. ##STR00001##