UV/Vis Spectroscopy of Metalloporphyrin and Metallophthalocyanine Monolayers Self-Assembled on Ultrathin Gold Films

Abstract

The use of evaporated ultrathin gold films on mica to obtain transmission UV/vis spectra of monomolecular overlayers containing chromophores is demonstrated. The gold substrates (thickness, 13-100 Å) were studied by scanning force microscopy, UV/vis spectroscopy, and X-ray diffraction and found to exhibit an array of {111} textured islands, whose sizes and optical properties can be controlled by the evaporation conditions and subsequent annealing. The use of gold substrates of this kind enables one to clearly resolve UV/vis absorption spectra of (sub)monolayers. This methodology is applied to the study of the binding of cobalt and iron tetraphenylporphyrins (CoTPP and FeTPPCl, respectively) and cobalt phthalocyanine (CoPc) to various N-donor ligand monolayers, self-assembled on ultrathin gold films. Enhancement of the gold surface plasmon absorption, resulting from molecular self-assembly on the gold island film, is used to semiquantitatively follow porphyrin binding to the monolayer.

Preparation of Gold Nanoisland Arrays from Layer-by-Layer Assembled Nanoparticle Multilayer Films

“…The morphologies of these nanoisland film arrays were quite comparable to those of nanoisland films prepared by vacuum evaporation method. [15][16][17][18][19][20][21][22] As shown in Figure 5, the nanoisland films generated from 8-nanoparticle layer films had more grains and the peak of the distribution moved to a lower value. Density of grains for nanoisland films from 5-and 8-nanoparticle layer films was estimated to be ~ 500 grains/µm 2 and ~ 950 grains/µm 2 , respectively.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] In LSPR sensing, the spot size can be minimized to a small number of individual sensing elements with an in-plane width of less than ~ 100 nm. Therefore, LSPR-based nanosensors can be extremely simple, small, and light.…”

“…In addition, the LSPR nanosensors can be used in both transmission mode and reflection mode. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] When UV-vis extinction spectroscopy in transmission geometry is used for sensing, it is known as transmission localized surface plasmon resonance (T-LSPR) sensing. The major advantage of T-LSPR sensing over conventional SPR sensing lies in the low-cost samples and simple experimental setup, which can be reduced to measurements at a single wavelength in a transmission configuration.…”

“…Rubinstein's method involves a preparation of ultrathin (less than 10 nm) semi-transparent gold island films by vacuum evaporation onto inert transparent substrates. [15][16][17][18][19][20][21][22] Van Duyne's nanosphere lithographic techniques involve the fabrication of arrays of triangular silver nanoparticles in the interstices between the elements of the nanosphere deposition mask. [8][9][10][11][12][13][14] The removal of the deposition mask following thermal deposition, pulsed laser deposition, or e-beam deposition of metal leaves triangular nanoisland arrays on the solid substrates.…”

Molecular Tips for Scanning Tunneling Microscopy: Intermolecular Electron Tunneling for Single-molecule Recognition and Electronics

“…The Au(111) substrate was initially modified with 4ATP via S-Au chemisorption; this 4ATP-modified substrate was then immersed in the CoTPP solution. These processes allow the immobilization of CoTPP on the Au surface through 4ATP by axial ligation, [58][59][60] with the consequent formation of the molecular assembly ( Fig. 10(a), right).…”