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 an anthracene or substituted anthracene 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; --C--C-- 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.