New Nanoscale Insights into the Internal Structure of Tetrakis(4-sulfonatophenyl) Porphyrin Nanorods

Abstract

Nanorods produced from the sodium salt of tetrakis(4-sulfonatophenyl) porphyrin, dissolved in acidic aqueous solutions, were deposited onto Au(111) substrates and imaged by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The AFM and STM images revealed individual rods with a diameters of 25-40 nm and lengths of hundreds of nanometers. Bundles of individual rods fashioned larger structures. We report for the first time high resolution STM images of TSPP on Au(111) which reveal that the rods are composed of disk-like building blocks approximately 6.0 nm in diameter. We speculate that the disks are formed by a circular J-aggregation of 14-16 overlapping electronically coupled porphyrin chromophores and that this circular porphyrin organization is driven by nonplanar distortions of the porphyrin diacid. The resonance Raman spectra of the solution phase aggregate and the surface-enhanced resonance Raman spectra of the aggregate on gold films were obtained at an excitation wavelength coincident with the exchange-narrowed J-band and found to be similar in peak frequencies and relative intensities. The UV-visible absorption spectrum of the solution phase aggregate was also found to be similar to that of the aggregate deposited on quartz. These comparisons confirm similar ground and excited electronic state structures of the excitonically coupled chromophores which comprise the aggregate in solution and on gold. Our results shed light on a number of previous experimental observations that could not be rationalized within the typical presumed staircase model of J-aggregation.

Exciton Level Structure and Dynamics in Tubular Porphyrin Aggregates

“…9,[21][22][23][24] The structure of TPPS4 tubular aggregates has been characterized by small angle X-ray scattering, atomic force microscopy (AFM), and cryo-electron microscopy. [25][26][27][28][29][30][31][32][33] TPPS4 tubular aggregates are found to be cylindrical structures with a diameter of approximately 16-18 nm 31,33 and a length up to several microns. As shown in Figure 1, these tubular aggregates can be viewed as a rolled-up 2D…”

Formation of Two‐Dimensional Supramolecular Polymers by Amphiphilic Pyrene Oligomers

“…[37][38][39][40][41][42][43][44][45][46] Moreover, spectroscopic changes often provide valuable information about the relative orientation of adjacent chromophores in a given environment. [39,[47][48][49][50] Among the most prominent examples of electronic interactions with pronounced effects is the formation of J-and H-aggregates. [51][52][53][54][55] The type of aggregation strongly depends on the geometry and orientation of the interacting molecules as described by the theory of exciton coupling.…”

Polyelectrolyte‐Assisted Noncovalent Functionalization of Carbon Nanotubes with Ordered Self‐Assemblies of a Water‐Soluble Porphyrin

“…Literature reports proposed models of ribbonlike building blocks for TSPP nanorods deposited on mica or HOPG 33. Recent results obtained by high‐resolution STM of TSPP nanorods deposited on Au(111) indicated the presence of disklike substructures formed by circular J‐aggregation of 14–16 porphyrin units as building blocks for the nanorods 18c. Cryo‐TEM and freeze–fracture TEM data also suggested the formation of hollow cylindrical (tubular) TSPP aggregates in aqueous solution which contain 25–26 macrocycles in diameter and vary from nanometers to micrometers in length 34…”