Further preferably, the compound according to the above [1], wherein R6 to R8 are the same or different and each is a hydrogen atom, a halogen atom, a lower alkyl, or a halogen-substituted lower alkyl and R9 is ???O. [8] The compound according to the above [1], wherein R10 in the above formula (I) is a hydrogen atom. [9] The compound according to the above [1], wherein the group represented by L i