W. Schrof et al., NONLINEAR-OPTICAL PROPERTIES OF NOVEL LOW-BANDGAP POLYTHIOPHENES, Journal of the Optical Society of America. B, Optical physics, 15(2), 1998, pp. 889-894
A new approach to polythiophene thin films with variable low-energy ba
ndgap is reported. Stille reaction [Angew. Chem. Int. Ed. Engl. 25, 50
8 (1986)] between a toolbox of different bis(trimethyltin)thiophenes a
nd dihalothieno[3,4-b]pyrazines produces polythiophenes with interesti
ng nonlinear optical properties. By variation of the substituent attac
hed to the pyrazine ring, the electronic and optical properties of the
polymer can be strongly influenced, for example, in lowering the band
gap (< 1 eV) or in increasing the oscillator strength. The improved os
cillator strength is accompanied by a longer conjugation length and le
ads to higher nonlinearities. Third-order susceptibilities, chi((3)),
of 10(-8) esu were achieved with figures of merit, chi((3))/alpha (whe
re alpha is the linear absorption coefficient), of as much as 2 x 10(-
13) esu cm. Frequency-tunable degenerate four-wave mixing experiments
revealed a strong wavelength dispersion of the figure of merit above t
he bandgap, in contrast to scaling laws empirically found by other gro
ups. (C) 1998 Optical Society of America.