Nonlinear optical properties of benzimidazobenzophenanthroline type ladder polymers

Third-order optical susceptibilities (χ(3)) of poly{(7-oxo-7, 10H-benz[de]imidazo[4′,5′:5,6]benzimidazo [2,1-a]isoquinoline-3,4:10,11-tetrayl)-carbonyl}, referred to as BBL, and poly(6,9-dihydro-6,9-dioxobisbenzimidazo[2,1b:1′,2′j] benzo[1mn]-[3,8]phenanthroline-3,12-diyl), known as BBB, have been determined using the technique of degenerate four-wave mixing (DFWM) at 1.064 μm. BBL has a χ(3)xxxx=(1.5±0.4)×10−11 esu, three times as large as that of BBB and 38 times as large as that of CS2. Electrochemical doping led to a small (<30%) increase in the third-order susceptibility of BBL.