Nonlinearity/transparency trade-off

The search for efficient NLO-phores includes also the design of octupolar derivatives [40, 70a]. The advantages associated with this alternative class of NLO-phore include an improved nonlinearity-transparency trade-off and more facile noncentrosymmetric arrangement in the solid state due to the absence of dipolar moments. To this end, the 3-D chromophores 135 and 136 with C3 and D2 (approximate T) symmetry, respectively (Scheme 4.39), have been prepared according to classical synthetic routes [73a]. 

Crystal violet, a trigonal conjugated cationic dye with electronic CT from peripheral dimethylamino donor groups to an electron deficient sp hybridized central carbon atom. A resonantly enhanced (3 value of 580 x 10 ° esu has been reported at 1.064 nm, in acetone solution = 590 nm) by Zyss et al. [16] The 1st hyperpolarizability, p, of crystal violet dye was measured at 1450 and 1500 nm by Rao et al. [91]. The resonance-free P value, p(°) for this octupole is comparable with that of the dipolar dye Disperse Red 1 but with the nonlinearity-transparency trade-off worse for the octupole. Symmetric cyanine dyes of the kind Me2N+ CH-(CH CH)n-NMe2 normally exhibit no first hyperpolarizabilities but have relatively long absorption... 

One shortcoming of the donor-bridge-acceptor design illustrated in Figures 1 and 2 is that increasing the nonlinearity is correlated with a red shift of the charge-transfer absorption band (the so-called nonlinearity-transparency trade-off). 

One of the most obvious approaches to defeating the putative optical nonlinearity-optical transparency trade-off follows from the theory of Marder and Perry and is illustrated in Fig. 1. When an amine donor group is connected to a thiophene bridging group, replacement of an alkyl amine with an aryl amine leads to an increase in bond length alternation and an accompanying blue shifting (increase in optical gap) of the interband electronic transition. Aryl to alkyl amine substitution leads, as expected from the theory of Marder and Perry, to an increase in molecular first hyperpolarizability (see Fig. 1), which is, as already noted, accompanied by an increase in optical transparency. This is in contrast to the more... 

The trade-off between transparency and nonlinearity is also seen in donor-acceptor organometallics as seen in Table I for a series of W(CO) 5 (4-substituted pyridine) complexes. 

All measurement results on molecules with X x below 37 6 nm have been included. The improved trade-off between nonlinearity and transparency of the fluorinated sulfonyl and SSI acceptors is evident. 

A series of solution-processible and tractable polymetallaynes of Pt and their mixed-metal analogues were demonstrated to be excellent OPL materials to nanosecond laser pulses at 532 nm, with optimized optical transparency/ nonlinearity trade-offs. The optical-limiting behavior of selected platinum(II) polyynes was investigated by the Z-scan technique. Polyynes 19, 21, 22, 27, 29,... 

The design and synthesis of NLO chromophores require simultaneous optimization of properties such as /x,/3 values, absorption characteristics, thermal stability, and processibility. In general, there is a trade-off between transparency and nonlinearity for NLO dye molecules. The increase of nonlinearity of chromophores often involves a red shift of the absorption maximum. From a practical point of view, however, it is desirable that absorption at wavelengths of interest be avoided. A careful selection of the electron-donating and -with-... 

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