The Effect of varying Ground-state Aromaticity on the First Molecular Electronic Hyperpolarizabilites of Organic Donor-Acceptor Molecules

A series of compounds of the form 4-dimethylaminophenyl–polyene–acceptor, where the polyene ranges from nothing to all-trans-1,3,5-hexatriene and the acceptor is 2-nitrovinyl, formyl, or 2,2-dicyanovinyl has been prepared and their β values measured by solution electric-field-induced second-harmonic generation; these molecules, which lose only one aromatic resonance upon charge-transfer excitation, show enhanced β compared to bi-aromatic molecules with the same substitution and total conjugation length, such as 4-dimethylamino-4′-nitrostilbene (DANS), a well-known benchmark for high β organic molecules

The First Molecular Electronic Hyperpolarizabilities of Highly Polarizable Organic Molecules: 2,6-Di-tert-butylindoanilines

The first molecular hyperpolarizabilities (β) of a series of 2,6-di-tert-butylindoanilines, measured by electric-field-induced second harmonic generation are somewhat more sensitive to donor strength than was found for analogously substituted nitrostilbenes, and dimethylindoaniline has a β roughly twice that of its 2,6 di-tert-butylated analogue, measured in chloroform; solvatochromic measurements on the former compound suggest that this decrease in hyperpolarizability is consistent with a bound-solvent effect

Synthesis and First Hyperpolarizabilities of Acceptor-substituted β-apo-8’-Carotenal Derived Compounds

The synthesis and second-order nonlinear optical properties of acceptor-substituted biologically derived β-apo-8′-carotenal compounds are reported; electric field-induced second harmonic generation (EFISH) measurements give values of β(0) which are 2–6 times greater than for 4-N,N-dimethylamino-4′-nitrostilbene (DANS)

The dependence of the molecular first hyperpolarizabilities of merocyanines on ground-state polarization and length

We report here the dipole moment (µ) and first hyperpolarizability (β) determined by electric field-induced second harmonic generation, for several merocyanine dyes containing an 1,3,3-trimethylindoline heterocycle as a ‘donor’ in which the ‘acceptor’ end of the molecule and the polyene bridge length was systematically varied; dyes with hexamethine bridges gave positive β, while that with a dimethine bridge gave a negative β value

Optimizing the second-order optical nonlinearities of organic molecules: asymmetric cyanines and highly polarized polyenes

e recently reported that there is an optimal combination of donor and acceptor strengths for a given molecular length and bridge structure that maximizes (beta) . For this combination, there is the correct degree of bond length alternation and asymmetry in the molecule. Our recent findings suggest that molecules that can be viewed as asymmetric cyanines with relatively small amounts of bond length alternation are nearly optimal. In this manner, we have identified molecules with nonlinearities many times that of conventional chromophores for a given length. In this paper, we will present a new computational analysis that allows the correlation of bond length alternation with hyperpolarizabilities and will present EFISH data on simple donor-acceptor polyene chromophores

Stronger acceptors can diminish nonlinear optical response in simple donor-acceptor polyenes

There has been much recent effort in the design of optimal chromophores for second-order nonlinear optical (NLO) applications. Most studies of organic molecules have focused on donor-acceptor π-conjugated molecules containing aromatic groups. We will show that the NLO response of aromatic donor-acceptor chromophores is dramatically different than their simple polyene analogs. Although there have been several computational studies of the first hyperpolarizability (β) of the simple organic donor-acceptor chromophores, the polyenes, few molecules in this class have been studied experimentally. These molecules are the prototypical conjugated donor-acceptor chromophores and as such can serve as a base line reference for both experimental and theoretical NLO structure/property relationships. Accordingly, we report the results of electric-field-induced second-harmonic generation (EFISH) studies of simple donor-acceptor polyenes as a function of donor and acceptor strengths and of molecular length

Optimizing the second-order optical nonlinearities of organic molecules: asymmetric cyanines and highly polarized polyenes

e recently reported that there is an optimal combination of donor and acceptor strengths for a given molecular length and bridge structure that maximizes (beta) . For this combination, there is the correct degree of bond length alternation and asymmetry in the molecule. Our recent findings suggest that molecules that can be viewed as asymmetric cyanines with relatively small amounts of bond length alternation are nearly optimal. In this manner, we have identified molecules with nonlinearities many times that of conventional chromophores for a given length. In this paper, we will present a new computational analysis that allows the correlation of bond length alternation with hyperpolarizabilities and will present EFISH data on simple donor-acceptor polyene chromophores

Experimental demonstration of the relationship between the second- and third-order polarizabilities of conjugated donor-acceptor molecules

The dependence of the second- and third-order polarizabilities ((beta) and (gamma) ) on ground-state polarization was measured for a series of donor-acceptor polyenes using electric field induced second harmonic generation and third harmonic generation, respectively. The changes in ground-state polarization, associated with the donor/acceptor strength or solvent polarity, were probed by x-ray crystallography, 1H-NMR, electronic absorption, and Raman spectroscopies. The observed behavior of (beta) and (gamma) as a function of ground- state polarization agrees well with theoretical predictions. In particular, positive and negative peaks, as well as sign changes, were observed for both (beta) and (gamma) . The dependences for (beta) and (gamma) are consistent with a derivative relationship between them. In addition, the third-order polarizability of a series of molecules possessing zero bond length alternation was found to be negative, in agreement with predictions based on the relationship between the polarizabilities and ground-state geometry