Time-Resolved and Near-Field Scanning Optical Microscopy Study on Porphyrin J-Aggregate

Abstract

Water-soluble porphyrin, 5,10,1 5,20-tetraphenyl-21Η,23Η-paorpahiυe-tetrasulfonic acid (TPPS), forms J-aggregate in aqueous solution depending on experimental conditions such as pH, dye concentration, and/or ionic strength. The steady-state fluorescence and picosecond single-photon timing spectroscopy were applied for protonated monomer and J-aggregate in aqueous solution and in thin films to reveal the dynamics in the S2 and S1 states. . The S2 fluorescence spectra from the protonated monomer and J-aggregate were observed in addition to the normal S 1 fluorescence. The lifetime of the S2 state was estimated to be 5 ps for J-aggregate, whereas the lifetime is shorter than 1 ps for protonated TPPS monomer. The mesoscopic structures of J-aggregate in thin film with and without polymer on the glass surface were examined by scanning near-field optical microscopy. With the surface topography and scanning near-field optical microscopy transmission images, TPPS J-aggregate was found to form a long and narrow tube-like structure which has a few μm length, 0.2-0.5 μm width, and 5-30 nm height. An unidirectional orientation of the structure was also found, which may be originated from the spin-coating process.

Spectral inhomogeneities and spatially resolved dynamics in porphyrin J-aggregate studied in the near-field

“…100 nm, and ca. 20 nm heights, which is similar to that reported for TSPP J-aggregate [9]. Similar structures have been also observed by the scanning electron microscopic images.…”

“…However, J-aggregates of porphyrin are less emissive, which makes fluorescence SNOM studies difficult. In this regard, Miura et al [9] studied morphology of TSPP J-aggregates by transmission mode SNOM in a single wavelength.…”

Assemblies of TPPS4 porphyrin investigated by TEM, SPM and UV–vis spectroscopy

“…To obtain detailed structural information about the supramolecular organization on surface for porphyrin selfassembled arrays the scanning tunneling microscopy (STM) [9,[26][27][28][29], atomic force microscopy (AFM) [16,28,29] and scanning near field optical microscopy (SNOM) [30,31] were employed in the last years. Scanning probe microscopy plays a paramount role, since they allow one to explore organic surfaces on different scale lengths in various ambients [32].…”

<title>Light propagation in scanning near-field optical microscopy probe</title>

“…Now the SNOM are used in the investigations of the applied problems in the surface physics4' , microscopy, lithography, recording and storage of the information68, studying of the polymers9, biological systems'°' ' and also in studying fundamental questions of the light interaction with atoms and molecules on the various substances surfaces and quantum dots of the semiconductors2' [12][13][14][15] There are many various modifications of the nearfield microscopy techniques16 ' 17 In the one of the most widespread variants of such technique, the light with wavelength X enters into the probe, which represents a metal coated taper fiber. The diameter of the probe output aperture is considerably to be smaller than the wavelength 2, that allows to focus the light into area ofthe substance surface with small cross-section area S << X2 then a probe is close enough to the surface (see Fig.…”