Solution DFWM chi((3)) non-linear optical properties of poly[(arylene)silylene]s and poly[(arylene)(ethynylene)silylene]s containing tetra- or hypercoordinate silicon

The third-order optical nonlinearities of a series of conjugated poly[(arylene)(ethynylene)silylene]s, and also of a complementary series of poly[(arylene)silylene] statistical copolymers without acetylene groups, have been studied in chloroform solution by using the degenerate four-wave mixing technique with a Q-switched Nd:YAG laser-oscillator at 1064 nm and a pulse duration of ca. 6 ns. The polymers contain a variety of arylene groups including carbazole and anthracene. The electronic and nuclear contributions of the chi((3)) susceptibility and the thermal nonlinearity of the solutions were separated. The chi((3)) susceptibilities of some poly[(arylene)(ethynylene)silylene]s were found to be as high as \Re chi((3))\=0.95x10(-10) esu for solutions of concentration 50 g l(-1). The results show that the presence of a single 8-(dimethylamino)naphthyl ligand at silicon affording pentacoordination has a beneficial effect on the chi((3)) properties. Comparison of the results for the poly[(arylene)silylene]s with those for the poly[(arylene)(ethynylene)silylene]s suggests that the absence of acetylene groups in the former case has in general a deleterious effect on the chi((3)) properties. Confirmation of the order of magnitude of the non-linear response has been confirmed by Z-scan measurements with picosecond laser pulses on hybrid sol-gel silica films of two of the poly[(arylene)(ethynylene)silylene]s containing arylene amide groups.