Photochemistry of conjugated polyacetylimes

Abstract

Some conjugated polyacetylenes were prepared successfully with moderate yields by proper coupling methods from comercially available cheap starting material. Trimethylsilylated 1, 3-butadiynes were directly introduced to the phenyl iodides to give 4`` using $PdCl_2(PPh_3)_2$ as a catalyst. Trimethylsilyl group contribute to the stability of the diyne unit(3``, 4``, and 9`` in Scheme 1 and 2). 1-Phenyl-1,3,5-heptatriyne was synthesized from 9``. The major advantage of this method is that the handling of these compounds is very easy because of the stabilization of triple bonds by trimethyl silyl groups. Irradiation of 1,4-diphenyl-1,3-butadiyne(DPB) with dimethyl fumarate(DMFu) in deaerated THF solution at 300 nm yields 1:1 photoadduct($\underline{1}$), and 1:2 photoadducts($\underline{2}$ and $\underline{3}$). The 1:1 photoadduct($\underline{1}$) is initially formed and prolonged irradiation of the solution results in the formation of 1:2 photoadducts($\underline{2}$ and $\underline{3}$) indicating that 1 is the primary and $\underline{2}$ and $\underline{3}$ are the secondary photoadducts. photolysis of pure 1 isolated with DMFu in THF results in $\underline{2}$ and $\underline{3}$ strongly supporting that $\underline{1}$ is the primary and $\underline{2}$ and $\underline{3}$ are the secondary photoadducts. Triplet quenching effects on the photoreactions with tetracene and oxygen showed that the photoreaction of DPB with DMFu to give 1 proceed via triplet excited state of DPB. Similar experiment for the secondary photoreaction showed that $\underline{2}$ and $\underline{3}$ are produced via singlet and triplet excited state of $\underline{1}$. Deaerated DMB solution of DPB was irradiated with UV light to obtain 1:1 photoadduct($\underline{4}$) and 1:2 photoadducts($\underline{5}$ and $\underline{6}$). Detailed investigation on the formation pathway of these adducts shows that $\underline{4}$ and $\underline{5}$ are produced via triplet excited state of DPB, whi...