This is the aminosquaric acid derivative L in which R3 is an n-butyl group and R1 and R4 are each a hydrogen atom, this derivative being the derivative of Formula II in which Q1 is a 2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping, R3 is a butyl group and R1 and R4 are each a hydrogen atom.