Browsing by Author "Breitung, EM"

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Synthesis and characterization of nonlinear optical chromophores with conformationally locked polyenes possessing enhanced thermal stability
(1999-06-01)
Shu, YC
;
Gong, ZH
;
Shu, CF
;
Breitung, EM
;
McMahon, RJ
Dipolar NLO chromophores with an interposed conjugated tetraene segment in which all but four of the methine groups are incorporated into a tetrahydronaphthalene framework have been synthesized and characterized. This conformation-locking approach furnishes NLO chromophores possessing an enhanced thermal stability. X-ray crystallographic data indicate that the polyenic chain of these molecules exhibits a near-planar all-trans conformation in the solid state. EFISH measurements show that these conformationally locked tetraenic chromophores exhibit large second-order optical nonlinearities (mu.beta similar to 4000 x 10(-48) cm(6) at 1907 nm), although the nonlinearities of the corresponding "unlocked" analogues are slightly larger.
Synthesis and characterization of thiazole-containing chromophores for second-order nonlinear optics
(1999-07-01)
Wang, YK
;
Shu, CF
;
Breitung, EM
;
McMahon, RJ
;
應用化學系
Push-pull thiazole-containing nonlinear optical chromophores with dicyanovinyl and tricyanovinyl accepters, along with their thiophene analogs, have been synthesized and characterized. The onset temperatures of thermal decomposition of these chromophores determined by DSC are:above;240 degrees C. The;redox properties of the chromophores were studied by cyclic voltammetry and the results reveal the electron-deficient (thiazole) and electron-excessive (thiophene) nature of the heterocycles. Experimental measurements of second-order nonlinear optical response (mu.beta) indicate that the combination of either,a thiazole or thiophene conjugating,unit and a tricyanovinyl acceptor results in a nonlinear optical chromephore exhibiting substantial molecular hyperpolarizability (mu.beta ca 7000 x 10(-48) cm(6) at 1907 nm).
Thiazole and thiophene analogues of donor-acceptor stilbenes: Molecular hyperpolarizabilities and structure-property relationships
(2000-02-16)
Breitung, EM
;
Shu, CF
;
McMahon, RJ
;
應用化學系
;
Department of Applied Chemistry
We calculate the first hyperpolarizability (beta) of several thiazole and thiophene analogues of donor-acceptor stilbene compounds using the ZINDO (sum-over-states) formalism. Because of the inherent dipolar nature of thiazole, in which C2 is electron-poor and C5 is electron-rich, the relative orientation of the thiazole subunit in the dipolar chromophore dramatically affects the nonlinear optical properties. In the "mismatched" case, the dipole of the thiazole ring opposes the molecular dipole created by the donor-acceptor substituents, while in the "matched" case, the dipole of the thiazole ring reinforces the molecular dipale. The hyperpolarizability of the "mismatched" monothiazole 2 (beta(mu) = 68 x 10(-30) cm(5) esu(-1)) exceeds that of stilbene 1 (beta(mu) = 34 x 10(-30) cm(5) esu(-1)) but is smaller than that of monothiophene 4 (beta(mu) = 90 x 10(-30) cm(5) esu(-1)). By contrast, the hyperpolarizability of the "matched" monothiazole 3(beta(mu) = 177 x 10(-30) cm(5) esu(-1)) exceeds not only that of the "mismatched" monothiazole 2, but also that of monothiophene 4. Substituting thiazole for both aryl rings of stilbene produces very large hyperpolarizabilities in the "matched-matched" case (e.g., bis-thiazole 24, beta(mu) = 254 x 10(-30) cm(5) esu(-1)). The nonlinear optical response of heterocyclic analogues of donor-acceptor stilbene derivatives is discussed in terms of the difference in aromatic delocalization energy between phenyl, thiophene, and thiazole, the electronic nature of the heteroaromatic rings, and conformational factors.