. "R8, ???NR8R9, where R9 is as just defined for R8 and may be the same or different, ???N02, ???CN, ???C02R8, ???SO3H, ???SOR8, ???SO2R8 ???OC02R8, ???CONR8R9, ???OCONR8R9, ???CSNR8R9, ???COR8, ???OCOR8, ???N(R8)COR9, ???N(R8)CSR9, ???SO2N(R8)(R9), ???N(R8)SO2R9, ???N(R8)CON(R9) (R10), where R10 is a hydrogen atom or an optionally substituted alkyl group, ???N(R8)CSN(R9)(R10) or ???N(R8)SO2N(R9)(R10" . . .