4-membered ring compound and optical phase retardation plate using the same

摘要

A 4-membered compound is represented by the following formula (I) is disclosed (in the formula, X<1> and X<2> each independently represent an oxygen atom, a sulfur atom or a substituted or unsubstituted imino group, Y<1> and Y<2> each independently represent a single bond, an oxygen atom or a substituted or unsubstituted imino group, B<1> and B<2> each independently represent an optionally substituted aliphatic, aliphatic carbonyl, aromatic or aromatic carbonyl group having 1-20 carbon atoms, and A<1> and A<2> each independently represent a group represented by the following formula (II) (Ar<1>, Ar<2> and Ar<3> each independently represent a cyclic group having 5-14 carbon atoms, L<1> and L<2> each independently represent a single bond or a divalent linking group, and p represents an integer of 0-2)). There is also disclosed a birefringence medium containing a 4-membered compound represented by the formula (I) and an optical element comprising the birefringence medium.