Structure-function relationships of second hyperpolarizabilities in two-dimensional molecules

The enhancement of the third order susceptibilities χ ⁽³⁾ and second order molecular hyperpolarizabilites < γ > in a series of convenlently stacked dimer and trimer macrocycles (SiPc and SiNc) was observed through the phase conjugated signals from DFWM measurements at both 1064 and 532 nm. The FWHM of the phase conjugated signals at 532 nm is much smaller than those at 1064 nm and those of the reference compound CS ₂. The < γ > values at both wavelengths as a function of number of the monomer units (n) have an approximate n ³ dependence, differing only in the scaling constant. The origin of such enhancement is discussed and compared to those in 1D π-conjugated systems.