Hexasubstituted donor-acceptor benzenes as nonlinear optically active molecules with multiple charge-transfer transitions

The synthesis of three novel nonlinear optical (NLO) chromophores with threefold symmetry, namely 1,3,5-tris(4-N,N-diethylaminophenyl)-2,4,6-tris(4-nitrophenyl)benzene (3), 1,3,5-tris(4-N,N-dihexylaminophenylbuta- diynyl)-2,4,6-tris(4-nitrophenyl)benzene (13) and 1,3,5-tris(4-N,N-dihexylaminophenylethynyl)-2,4,6-tris(4-nitrophenylethynyl)benzene (4b), is reported. We used the [Co-2(CO)(8)]-catalysed trimerisation of 4-N,N-diethylamino-4'-nitrotolane (5) to prepare 3. The trimerisation experiment carried out with 1-(4-N,N-diethylaminophenyl)-6-(4-N,N-nitrophenyl)hexatriyne (6) and [Rh(PPh3)(3)Cl] afforded 13. A stepwise approach was used to prepare 4b. 1,3,5-Trichloro-2,4,6-triiodobenzene (8b) was coupled with 4-nitrophenyl-acetylene (14) under Pd-0 catalysis to yield 1,3,5-trichloro-2,4,6-tris(4-nitrophenylethynyl)- benzene (15). The coupling reaction of 15 with 4-N,N-dihexylaminophenylethynyltributylstannane (21) led to 4b.