The new salts trans-4ยข-(dimethylamino)-N-R-4-stilbazolium hexafluorophosphate (R = methyl, Me 1, phenyl, Ph 2, 2,4-dinitrophenyl, DNPh 3, 2-pyrimidyl, Pym 4, Scheme 1) have been prepared. Their electronic absorption spectra show intense, visible intramolecular charge-transfer bands, the energy (E max ) of which decreases in the order R = Me > Ph > DNPh > Pym. This trend arises from the steadily increasing electron deficiency of the pyridinium ring, a phenomenon also observed in cyclic voltammetric and 1 H nuclear magnetic resonance (NMR) data. Fluorescence-free first hyperpolarizability b values of [1ยฑ4]PF 6 were measured by using femtosecond hyper-Rayleigh scattering (HRS) with acetonitrile solutions and a 1300 nm laser, and static first hyperpolarizabilities b 0 were obtained by application of the two-state model. The HRS results indicate that the N-aryl chromophores in [2ยฑ4]PF 6 have considerably larger b 0 values than their N-methyl counterpart in [1]PF 6 , with a ca. 10-fold increase in b 0 observed in moving from [1]PF 6 to [4]PF 6 (25 ยฎ 230 10 ยฑ30 esu). Stark (electroabsorption) spectroscopic studies in butyronitrile glasses at 77 K allowed the derivation of dipole moment changes Dl 12 (10.9ยฑ14.8 D), which have been used to calculate b 0 according to the two-state equation b 0 = 3Dl 12 (l 12 ) 2 /2(E max ) 2 (l 12 = transition dipole moment). With the exception of [1]PF 6 , the Stark-derived b 0 values are in reasonable agreement with those from HRS. However, the increase in b 0 in moving from [1]PF 6 to [4]PF 6 is only 2-fold for the Stark data (90 ยฎ 185 10 ยฑ30 esu). The observed trend of increasing b 0 in the order [1]PF 6 < [3]PF 6 < [2]PF 6 < [4]PF 6 arises from a combination of decreasing E max and increasing Dl 12 , with only a slight increase in l 12 between [1]PF 6 and [4]PF 6 . It is likely that the b 0 values for [3]PF 6 are lower than expected due to the steric effect of the ortho-NO 2 group, which causes twisting of the DNPh ring out of the plane of the stilbazolium unit. A single crystal X-ray structure shows that [2]PF 6 crystallizes in the space group Cc, with head-to-tail alignment and almost parallel stacking of the pseudo-planar stilbazolium portions of the cations to form polar sheets within a polar bulk structure. [2]PF 6 is essentially isostructural with the related Schiff base salt trans-4-[(4-dimethylaminophenyl)iminomethyl]-N-phenylpyridinium hexafluorophosphate ([8]PF 6 ). Second harmonic generation (SHG) studies on [2]PF 6 and [8]PF 6 using a 1907 nm laser and sieved powdered samples (53ยฑ63 lm) afforded efficiencies of 470 and 240 times that of urea, respectively. Under the same conditions, the well-studied compound [1]p-MeC 6 H 4 SO 3 gave an SHG efficiency of 550 times that of urea.