Soluble and rigid terpyridine-based ditopic ligands bearing one to five phe
nylene/ethynylene modules have been synthesized by way of a stepwise proced
ure. Each module is attached to the terpyridine unit via an ethynylene frag
ment and functionalized at the 4-position with an additional ethynylene con
nector and in the a,5-positions with two flexible dodecyloxy chains. The sy
nthetic protocol is based on sequential Pd(0)-catalyzed cross-coupling reac
tions between a terpyridine subunit grafted with the necessary diethynyl/ph
enyl or ethynylphenyl/bromide appendage. For ditopic ligands displaying an
even number of phenyl/ethynylene modules, the final step involves a single
cross-coupling reaction between 4'-ethynylene-2,2':6',6"-terpyridine and th
e appropriate bromo derivative. In the case of the ligands having an odd nu
mber of phenylene/ethynylene fragments, a double cross-coupling reaction be
tween an extended dibromopolyphenylene intermediate and 4'-ethynylene-2,2':
6',6"-terpyridine or 1-(4'-ethynylene-2,2':6',2"-terpyridine)-4-ethynylene-
2,5-didodecyloxy- benzene is required. For ligands I-V, optimal preparative
conditions were found with [Pd-0(PPh3)(4)] (6 mol %) in n-propylamine at 7
0 degrees C. Qxidative dimerization of the 1-(4'-ethynylene-2,2':6',2"-terp
yridine)-4-ethynylene-2,5-didodecyloxybenzene derivative in the presence of
cupric salts and oxygen gives the corresponding homoditopic ligand II2 bea
ring a central diphenyldiacetylene spacer. Spectroscopic data for the new o
ligomers are discussed in terms of the extent of pi-electron conjugation. U
pon increasing the number of phenylene/ethynylene modules, there is a progr
essive lowering in energy of absorption and fluorescence transitions.