A process for the preparation of a squarylium compound of the formula: ##STR23## in which Q1 and Q2 are each a pyrylium, thiopyiylium, selenopyrylium, benzpyrylium, benzthiopyrylium or benzselenopyrylium nucleus, R1 and R2 are each independently a hydrogen atom or an alkyl group containing not more than about 6 carbon atoms, and one of R3 and R4 is a hydrogen atom and the other is a toluenesulfony