Surface-Enhanced Raman Scattering Characteristics of 4-Aminobenzenethiol Derivatives Adsorbed on Silver

초록

The most unusual feature in the surface-enhanced Raman scattering (SERS) of 4-aminobenzenethiol (4-ABT) is the appearance of b(2)-type bands in the region of 1100-1500 cm(-1) which, in recent years, has given rise to a dispute over their origin. In order to resolve this dispute, we have examined the SERS spectral pattern of 4-ABT derivatives adsorbed on Ag substrates. At first, we found in the SERS spectra of 4-(diethylamino)benzenethiol and 4-(benzylideneamino)benzenethiol that no photoreaction had taken place at all, but the b2-type bands appeared distinctly as is usual in the SERS of 4-ABT. The b2-type bands were also observed in the SERS spectra of other 4-ABT derivatives while, to our surprise, no such b2-type bands were observed at all in the SERS spectra of para-substituted (but not amino) benzenethiol derivatives. The appearance of the b2-type bands in the SERS spectra seemed thus a common feature of 4-ABT derivatives. The difference between 4-ABT derivatives and para-substituted (but not amino) benzenethiol derivatives was supposedly associated with the LUMO-HOMO energy gap. The energy gap computed for 4-ABT derivatives (similar to 300 nm) was consonant with the interpretation that the appearance of the b2-type bands in the SERS spectrum of 4-ABT is associated with an intensity borrowing from an intense pi -> pi* molecular transition ((1)A(1) -> B-1(2)) at 300 am.

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