In formulae (F2a) to (F4a), R57 to R68 each independently represents a hydrogen atom, a fluorine atom or an alkyl group, provided that at least one of R57 to R61, at least one of R62 to R64 and at least one of 65 to R6s are a fluorine atom or an alkyl group (preferably having a carbon number of 1 to 4) with at least one hydrogen atom being substituted by a fluorine atom.