The synthesis of paraphenylene acetylenes is introduced, following a concept which makes a complete homologous series -(p-C6H4-C=C)-n accessible. Systematic linkage with electroactive units leads to highly conjugated donor-acceptor systems. Organometallic substituted representatives satisfy the prerequisites for compounds with nonlinear optical properties : 4,4’-diethynyltolan I; 4-acetyl-4’-ethynyltolan II; 1,4-bis(4-acetylphenylethynyl)benzene III; 4-ethynyl-4’-(2-ferrocenylethynyl)tolan IV; 4-(2-ferrocenylethynyl)-4’-[2-(pentafluorophenyl)ethyny]tolan V; 4,4’-bis(2-ferrocenylethynyl)tolan VI; 4,4’-bis(2-cobaltocenyliumethynyl)tolan dihexafluorophosphate VII; 4-(2-cobaltocenyliumethynyl)-4’-(2-ferrocenylethynyl)tolan hexafluorophosphate VIII, 1,1’-bis(2-ferrocenylethynylphenylethynylphenylethynyl)ferrocene IX, 4-(2-cobaltocenyliumethynyl)-4’-ethynyltolan hexafluorophosphate X and 1,1’-bis(ethynylphenylethynylphenylethynyl)ferrocene XI are presented.