SERS Properties of Gold Nanorods at Resonance with Molecular, Transverse, and Longitudinal Plasmon Excitations.
The amplification of Raman signals of the heteroaromatic cation 1-(N-methylpyrid-4-yl)-2-(N-methylpyrrol-2-yl)ethylene (PEP+)) bound to Au nanorods (NRs) was investigated at different excitation wavelengths to study the effect of the laser resonance with the absorption band of thePEP+moiety and with the two plasmon oscillation modes of the NR. Two differentPEP+derivatives, differing in the length of the alkyl chain bearing the anchoring group, were used as target molecules. Raman spectra obtained exciting at 514 or at 785 nm (i.e., exciting the transverse or the longitudinal plasmon band) present a higher intensity than that at 488 nm suggesting a higher Raman amplification when the laser excitation wavelength is resonant with one of the two plasmon modes. Moreover, considering results of Discrete Dipole Approximation (DDA) calculations of the local field generated at the NR surface when either the transverse or the longitudinal plasmon modes are excited, we deduced that the resonance condition of the 514-nm laser excitation with the absorption band of the dye strongly contributes to the amplification of the Raman signal.
Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy ; INSTM, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
Ida
I
Ros
Department of Chemistry, University of Bari, Via Orabona 4, Bari, 70126 Italy.
Tiziana
T
Placido
Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
Vincenzo
V
Amendola
Department of Materials Science and INSTM, University of Milano-Bicocca, Via Cozzi 53, 20125 Milano, Italy.
Chiara
C
Marinzi
Department of Materials Science and INSTM, University of Milano-Bicocca, Via Cozzi 53, 20125 Milano, Italy.
Norberto
N
Manfredi
CNR-IPCF Division of Bari, c/o Department of Chemistry, University of Bari, Via Orabona 4, Bari, 70126 Italy.
Roberto
R
Comparelli
CNR-IPCF Division of Bari, c/o Department of Chemistry, University of Bari, Via Orabona 4, Bari, 70126 Italy.
Marinella
M
Striccoli
Department of Chemistry, University of Bari, Via Orabona 4, Bari, 70126 Italy ; CNR-IPCF Division of Bari, c/o Department of Chemistry, University of Bari, Via Orabona 4, Bari, 70126 Italy.
Angela
A
Agostiano
Department of Materials Science and INSTM, University of Milano-Bicocca, Via Cozzi 53, 20125 Milano, Italy.
Alessandro
A
Abbotto
Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
Danilo
D
Pedron
Department of Chemical Sciences, University of Padova and INSTM, Via Marzolo 1, 35131 Padova, Italy.
Roberto
R
Pilot
Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy ; INSTM, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
Renato
R
Bozio
Gold nanorods; Localized surface plasmon resonance; Nonlinear optics; Push–pull molecule; SERS