The present invention relates to compounds of formula (I)ArCH.sub.2 R.sup.1 (I)or a monomethyl or a monoethyl ether thereof (the compound of formula (I) including these ethers may contain no more than 30 carbon atoms in total); ethers, esters thereof; acid addition salts thereof; wherein Ar is a pyrene or substituted pyrene ring system; R.sup.1 contains not more than eight carbon carbon atoms and is a group ##STR1## wherein m is 0 or 1; R.sup.5 is hydrogen;R.sup.6 and R.sup.7 are the same or different and each is hydrogen or C.sub.1-3 alkyl optionally substituted by hydroxy;R.sup.8 and R.sup.9 are the same or different and each is hydrogen or C.sub.1-3 alkyl; ##STR2## is a five- or six-membered saturated carbocyclic ring; R.sup.10 is hydrogen, methyl or hydroxymethyl;R.sup.11, R.sup.12 and R.sup.13 are the same or different and each is hydrogen or methyl;R.sup.14 is hydrogen, methyl, hydroxy, or hydroxymethyl.