. . "It is desirable for R46 and R47 each to be an alkyl group (which contains preferably 1 to 20, more preferably 1 to 12, particularly preferably 1 to 8, carbon atoms) or an aryl group (which contains preferably 6 to 30, more preferably 6 to 20, particularly preferably 6 to 12, carbon atoms) , preferably an alkyl group." . . .