Examples of the RCOO-- group include, for example, CH.sub.3 COO-- andC.sub.2 H.sub.5 COO--.Examples of the organic compound having the group represented by the general formula (I) includes those compounds represented by the general formula (II):where A represents a group having 1 to 4 aromatic rings, Y is a group represented by the general formula (III), attached to the aromatic ring: ##STR6## whe