Concentration dependent Raman study of 1,4-diethynylbenzene on gold nanoparticle surfaces

Concentration dependent adsorption behaviors of 1,4-diethynylbenzene (DEB) on gold nanoparticle surfaces have been investigated by means of surface-enhanced Raman scattering (SERS). The spectral features including the multiple peaks in the ν(CC)bound stretching region were found to vary as the bulk concentration of DEB in gold nanoparticles. At a low concentration of 10−6 M, only the multiple ν(CC)bound band was conspicuous at ∼2000 cm−1 and the free CC stretching band was barely detected in the SERS spectra. When the bulk concentration was increased, the ν(CC)free band became prominent at ∼2104 cm−1. These splitting bands may provide the evidence that DEB is adsorbed on gold mainly through one of the two acetylene groups with the other CC groups being pendent with respect to the gold surface. Ab initio density functional theory (DFT) calculations of DEB were performed to check the vibrational assignment.