Molecular-Resolution Interrogation of a Porphyrin Monolayer by Ultrahigh Vacuum Tip-Enhanced Raman and Fluorescence Spectroscopy.
Tip-enhanced Raman scattering (TERS) and optically excited tip-enhanced fluorescence (TEF) of a self-assembled porphyrin monolayer on Ag(111) are studied using an ultrahigh vacuum scanning tunneling microscope (UHV-STM). Through selectively exciting different Q-bands of meso-tetrakis- (3,5-ditertiarybutylphenyl)-porphyrin (H2TBPP), chemical information regarding different vibronic excited states is revealed by a combination of theory and experiment; namely, TERS and time-dependent density functional theory (TDDFT) simulations. The observed TEF spectra suggest a weak coupling of H2TBPP to the substrate due to the bulky t-butyl groups and a possible alternative excited state decay path. This work demonstrates the potential of combining TERS and TEF for studying surface-mounted porphyins on substrates, thus providing insight into porphyrin-sensitized solar cells and catalysis.
Naihao
N
Chiang
Nan
N
Jiang
⊥Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Dhabih V
DV
Chulhai
Eric A
EA
Pozzi
Mark C
MC
Hersam
⊥Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Lasse
L
Jensen
Tamar
T
Seideman
Richard P
RP
Van Duyne
D011166:Porphyrins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013059:Spectrum Analysis, Raman; D014618:Vacuum
D011166:Porphyrins
time-dependent density functional theory (TDDFT); tip-enhanced Raman spectroscopy (TERS); tip-enhanced fluorescence (TEF); ultrahigh vacuum scanning tunneling microscopy (UHV-STM)