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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 19, Number 3
BKCSDE 19(3)
March 20, 1998 

Theoretical Study of the Nonlinear Optical Properties of Thiophene, Furan, Pyrrole, (1,2,4-triazole), (1,3,4-oxadiazole), and (1,3,4-thiadiazole) Monomers and Oligomers
U-Sung Choi*, Tae-Won Kim, Seung-Woo Jung, Cheol-Ju Kim
PM3 semiempirical calculations were carried out to study the frequency-dependent nonlinear optical properties of thiophene, furan, pyrrole, (1,2,4)-triazole, (1,3,4)-oxadiazole, and (1,3,4)-thiadiazole monomers and oligomers. The longitudinal component, αxx, is the largest of three principle components. On the other hand, the out-of-plane component, αzz, is the smallest. Moreover, the out-of-plane component (αzz) of thiophene, furan, pyrrole, (1,2,4)-triazole, (1,3,4)-oxadiazole, and (1,3,4)-thiadiazole monomers show constant changes with increasing optical frequencies. The frequency-dependent first- order polarizabilities increase in the order: thiophene (1,2,4)-triazole pyrrole furan (1,3,4)-thiadiazole (1,3,4)-oxa-diazole monomers and oligomers. The effects of β(-2ω;ω,ω) (SHG) shows a larger dispersion compared with (-ω;ω,0) (EOPE) and β(0;-ω,ω) (OR). The second- order polarizabilities of thiophene, furan, pyrrole, (1,2,4)-triazole, (1,3,4)-thiadiazole, and (1,3,4)-oxadiazole monomers for the various second- order effects have the order: β(-2ω;ω ,ω) (SHG) β(-ω;ω,0) (EOPE) β(0;-ω,ω) (OR) and thiophene pyrrole (1,2,4)-triazole furan 1,3,4-thiadiazole 1,3,4-oxadiazole monomers. The third- order polarizabilities for the various third- order effects have the following order: γ (-3ω;ω',ω,ω) (THG) γ(-2ω;0,ω,ω) (EFISHG) γ(-ω;ω',-ω,ω) (IDRI) γ(-ω;0,0,ω) (OKE). The effects of THG increase rapidly with increasing optical frequencies compared with the other effects. In particular, OKE effects increase most slowly with increasing optical frequencies. Also, the effects of THG for thiophene, furan, pyrrole, (1,2,4)-triazole, (1,3,4)-thiadiazole, and (1,3,4)-oxadiazole oligomers show the order thiophene (1,2,4)-triazole furan pyrrole (1,3,4)-thiadiazole (1,3,4)-oxadiazole oligomers. In particular, the third- order polarizabilities of thiophene and (1,3,4)-thiadiazole oligomers are about four and three times larger than those of (1,3,4)-oxadiazole and (1,2,4)-triazole oligomer, respectively.
299 - 307
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