Nonlinear optical properties of modified carbocyanines

We studied the optical nonlinearities of modified 3,3'-diethylthiadicarbocyanine iodides (X-DTDCI) in dimethyl sulfoxide (DMSO) solutions (X=H, Cl, Br at meso position) by a pump-probe technique with crossed polarized chirped laser pulses at room temperature. Reverse-saturable-absorption (RSA) with monoexponential lifetimes is observed at 532 nm in all the samples studied. We determined the effective excited-state absorption cross-sections and their lifetimes for an the samples investigated and found that they clearly correlate to the substituent X at the meso position. Empowered by the chirped pulses, a much faster nonlinearity with a decay time of similar to 3.1 ps that is much shorter than the laser pulses used, is unveiled in Cl-DTDCI. We expressed both the absorptive and the refractive part of this fast nonlinearity as the equivalent molecular hyperpolarizability gamma(1212) and found gamma(1212) = (81 + i9.8) x 10(-32) erg(-1).