A method of preparing a compound of the general formula: ##STR1## in which: R.sup.1 and R.sup.2 independently represent a hydrogen atom, an alkyl or substituted alkyl group, an aryl or substituted aryl group, an aralkyl or substituted aralkyl group, a cycloaliphatic or substituted cycloaliphatic group or a heterocyclic or substituted heterocyclic group providing R.sup.1 and R.sup.2 do not both represent cyclic groups of aromatic nature, or R.sup.1 and R.sup.2 together may represent the necessary atoms to complete a non-aromatic heterocyclic ring,R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently represent a hydrogen atom or any substituent providing the sum of their .sigma..sub.p constants has a value of less than +0.5, or R.sup.3 and R.sup.4 and/or R.sup.5 and R.sup.6 may represent the necessary atoms to complete an alicyclic or aromatic ring, R.sup.3 and R.sup.2 and/or R.sup.1 and R.sup.6 may represent the necessary atoms to complete a non-aromatic heterocyclic ring,R.sup.7 and R.sup.9 independently represent a hydrogen atom or any carbon linked substituent containing up to 16 carbon atoms,R.sup.8 and R.sup.10 independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or any two adjacent substituents R.sup.7, R.sup.8, R.sup.9 and R.sup.10 together may complete an alicyclic or aromatic ring, andX.sup.- represents an anion,comprising reacting an amine of the general formula: ##STR2## in which R.sup.1 to R.sup.6 are as defined above, with a thiopyrylium salt of the general formula: ##STR3## in which X.sup.- and R.sup.7 to R.sup.10 are as defined above, to yield the desired compound.The compounds of formula (I), many of which are new, are useful as sensitizers or photoconductors.