Xuan-Ming Duan

Second-Order Hyperpolarizabilities of Organic Ionic Species

Abstract The second-order hyperpolarizabilities (β) of two categories of organic ionic species were evaluated by the hyper Rayleigh scattering method. The ⟨β⟩ of (dimethylamino)stilbazolium analogues in methanol with long cut-off wavelength more than 600 nm, which can be used for electro-optic modulation, were evaluated to be in the order of 10−27 esu using 1064 nm light as a fundamental beam. Aromatic sulfonates in the second category were found to have comparatively large |β| values irrespective of short cut-off wavelength: In the case of sodium p-toluenesulfonate with cut-off of 280 nm, |β| in methanol was 2.2×10−29 esu and was about two thirds of p-nitroaniline with cut-off of 445 nm.

Evaluation of |β| of stilbazolium p-toluenesulfonates by the hyper Rayleigh scattering method

The hyper Rayleigh scattering (HRS) method was applied to determine the absolute value of second-order hyperpolarizabilities ((beta) ) of stilbazolium p-toluenesulfonates and related ionic species in methanol. In general, the (beta) values of stilbazolium derivatives become large with increasing wavelength of absorption maximum and are 1.1 X 10-28 - 3.9 X 10-28 esu, i.e., 3 - 10 times larger than (beta) of p-nitroaniline. By way of exception, halogenated stilbazoliums showed rather larger (beta) compared with the unsubstituted stilbazolium having almost the same absorption cutoff and maximum. The calculated d value of hydroxystilbazolium p-toluenesulfonate obtained using the present (beta) and the known crystal structure agreed well with the experimental d value by the Maker fringe method.

Second-Order Hyperpolarizabilities of Aromatic Carboxylates without Visible Absorption

The second-order hyperpolarizabilities (β) of aromatic carboxylates were evaluated by the hyper Rayleigh scattering method at 1.064 µ m and semiempirical molecular orbital calculation. The β values of methyl methoxybenzoate and its dimer in methanol solution were measured to be 22 and 49×10-30 esu, respectively, which are about 0.6 and 1.3 times that of p-nitroaniline. The calculation of β and dipole moment (µ ) of the methyl methoxybenzoate oligomers revealed an almost linear increase of these values with increasing number of repeating units up to trimers. Since the oligomers have a short cutoff wavelength of about 300 nm as well as large β and µ, these compounds are concluded to be promising chromophores for second-order nonlinear optics.

Comparatively Large Second-Order Hyperpolarizability of Aromatic Sulfonate Anion with Short Cutoff Wavelength

The second-order hyperpolarizabilities (β) of ionic species of sodium p-toluenesulfonate ( pTSNa) and its corresponding neutral derivative methyl p-toluenesulfonate ( p TSMe) in methanol were evaluated to be 2.2×10-29 and 1.2×10-29 esu, respectively, using the hyper Rayleigh scattering method at 1064 nm. Since ionic p TSNa has short cutoff wavelength of 280 nm as well as comparatively large |β| value, i.e., about twice that of neutral p TSMe and about two-thirds that of p-nitroaniline, aromatic sulfonate ions are concluded to be worth investigating as potential chromophores for second-order nonlinear optics.

Synthesis and non-linear optical properties of aromatic ester oligomers as chained chromophores

We synthesized some aromatic ester oligomers consisting of repeating units of oxy-1,4-phenylenecarbonyl group (ArESn, n = 2–4) as novel non-linear optical (NLO) active chromophores. Some second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 or 5 wt% ArESn and 10 wt% p-nitroaniline (pNA) were investigated. Comparison of the d33 value at the chromophore molar concentration [d33 (M)] for these polymer films indicated that the d33 (M) value of ArESn increases with an increase in n and ArESn with n more than 3 reveals a higher d33 (M) value than that of pNA. In addition, every ArESn has a cutoff wavelength (λco) of about 300 nm, which is much shorter than the case of pNA (λco = ca.45O nm). ArESn are concluded to be promising chromophores for second-order non-linear optics.

Synthesis and nonlinear optical properties of end-group modified aromatic esters as chained chromophores

We synthesized aromatic ester derivatives with some electron accepting groups at molecular ends as new class of nonlinear optical (NLO) active chromophores (ArESn-X, n = 2, 3, X = CN, CF 3 , NO 2 , DCV). Some second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn-X (ArESn-X/PMMA) were investigated. UV/vis spectra of these polymer films have cutoff wavelengths (λ co ) of about 300-380 nm, which are much shorter than in the case of p-nitroaniline (pNA) (λ co = ca. 450 nm) as a typical strong donor-acceptor (D-A) molecule. In addition, some of these polymer films exhibited larger second-order nonlinear coefficient (d 33 ) values than PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8 x 10 -9 esu). Namely, ArES3-CN (d 33 = 3.1 x 10 -9 esu, 10 wt.-% in PMMA), ArES3-NO 2 (3.0 x 10 -9 esu, 10 wt.-% in PMMA) and ArES2-DCV (4.0 x 10 -9 esu, 10 wt.-% in PMMA) showed not only excellent second-order NLO activity but also excellent transparency in the visible region (λ co = 304 nm (ArES3-CN), 340 nm (ArES-NO 2 ) and 370 nm (ArES2-DCV), respectively). Consequently, these compounds are believed to be promising chromophores for second-order nonlinear optics.

Organic Species with Short Cutoff Wavelength and Large Second-Order Hyperpolarizability

Abstract In order to find short cutoff and large β materials for second-order nonlinear optics, a series of substituted aromatic carboxylate anions and esters were investigated by semiempirical molecular orbital calculation. Methyl benzoates with a weak donor or benzoate anions with a weak acceptor at para-position were found to satisfy those conditions. Among them, optical properties of methyl 4-methoxybenzoate and its oligomers were studied by both calculation and experiment. The μβ values of oligomers consisting of N monomeric units were found to become N-times larger than the sum of N isolated monomers, though the absorption cutoff of oligomers stays almost the same as that of methyl 4-methoxybenzoate.

Synthesis and nonlinear optical properties of aromatic esters with an electron donor and an electron acceptor end group

We synthesized a series of aromatic esters having an electron donating and an electron accepting end group as a new class of nonlinear optical (NLO) active chromophores (ArESn D-A, n=2,3, D=MeO (as reference), MeS and Me 2 N, A=CN). Second-order NLO properties for poled polymer films consisting of poly(methyl methacrylate) (PMMA) doped with 10 wt.-% ArESn D-A (ArESn D-A/ PMMA) were investigated. The UV/vis spectra of these polymer films have cutoff wavelengths (λ co ) of about 350∼370 nm, which are much shorter than in the case of p-nitroaniline (pNA) (λ co =473 nm) which is a typical strong donor-acceptor (D-π-A) molecule. In addition, some of these polymer films exhibit higher second-order nonlinear coefficients (d 33 ) than a PMMA film doped with 10 wt.-% pNA (pNA/PMMA) (2.8X10 -9 esu). Namely, ArES3 Me 2 N-CN (d 33 =5.6X10 -9 esu, 10 wt.-% in PMMA) and ArES2 Me 2 N-CN (3.8X10 -9 esu, 10 wt.-% in PMMA) showed excellent second-order NLO activity as well as transparency in the visible region (λ co : 362 nm for ArES3 Me 2 N-CN and 366 nm for ArES2 Me 2 N-CN, respectively.

Synthesis and Nonlinear Optical Properties of Polymers Containing Aromatic Ester Oligomers as Chained Chromophores

Abstract We synthesized some aromatic ester oligomers consisting of repeating units of oxy-1,4-phenylenecarbonyl group (ArESn, n=2∼4) as novel nonlinear optical (NLO) active chromophores and their methacrylate derivatives (ArESn-MA, n=2∼3). Some second-order NLO properties for poled polymer films of poly(methyl methacrylate) doped with 10 or 5wt% ArESn (ArESn/PMMA) and ArESn-MA homopolymers (poly(ArESn-MA)) as well as copolymers with MMA (poly(ArESn-MA-co-MMA)) were estimated by the second harmonic generation (SHG) measurement using Nd-YAG laser as light source. Comparison of the d33 value at the chromophore molar concentration (d33 (M)) for ArESn/PMMA films indicated that the d33 (M) value of ArESn increases with increase in n and ArESn with n more than 3 reveal higher d33 (M) value than that of pNA, in addition, every ArESn has cutoff wavelength (λco) of about 300nm, which is much snorter than the case of pNA (λco=ca. 450nm). Moreover, poly(ArESn-MA) films exhibited much larger d33 values than those of ...

First hyperpolarizability of benzoate anions and esters

The molecular first hyperpolarizability (β) of a series of benzoate anions and their esters were measured by the hyper-Rayleigh scattering (HRS) in methanol solution. The effect of the presence of methanolic solvation on their β values were calculated and clearly correlates to the experimental β. The static β values of some of the benzoate anions were evaluated and found to be close to those of pNA irrespective of the cutoff wavelengths being shorter than 400 nm, and the absorption maximum shorter than those of corresponding esters. These new anions would be promising starting compounds for ionic crystalline second-harmonic generation (SHG) material of diode laser.