In a further embodiment, where any of R1 to R14 is directly substituted by an aryl substitutent group, or by an aryl-containing substituent group (such as aryloxy or arylaminocarbonylamino for example), then the aryl moiety of the substituent group directly attached to any of R1 to R14 may be further substituted by the substituent groups hereinbefore described and particularly by halogen, alkyl (s