Microscopic Organization of Long-Chain Rhodamine Molecules in Monolayers at the Air/Water Interface

Abstract

The monolayer behavior of a rhodamine derivative with two C 18 aliphatic chains attached to the nitrogen atoms of the xanthene ring system (RhC 18 ) was studied by epifluorescence microscopy, second-harmonic generation (SHG), and absorption and fluorescence spectroscopy. The isotherm of RhC 18 exhibits a plateau which, presumably, corresponds to a slow collapse of the monolayer. As observed by epifluorescence microscopy, the RhC 18 monolayer remained homogeneous for a large range of molecular areas, and an abrupt change in the monolayer morphology occurred at the end of the surface pressure isotherm. Spectroscopic data showed that both fluorescent J-aggregates and nonfluorescent H-aggregates with a coplanar-inclined configuration were formed within the RhC 18 monolayer upon compression. The orientational SHG measurements revealed that, in the expanded region of the isotherm, the RhC 18 chromophore was oriented in a way where its xanthene plane made an angle of 36°with respect to the interface. The azimuthal angle SHG measurements revealed that compression induced an anisotropic arrangement of the S 0 -S 1 transition moment of RhC 18 chromophores perpendicular to the compression direction. At the end of the isotherm prior to and after the collapse point, the film possessed a fairly regular structure characterized by a C 2V symmetry packing and a long-range order in the parallel alignment of the RhC 18 chromophores. Microscopic organization of the RhC 18 molecules in monolayers is discussed.

Spectroscopic properties of mixed Langmuir–Blodgett films of rhodamine dyes and poly(N,N-diallyl-N-octadecylamine-alt-maleic acid)

“…Rhodamine dyes which have a high fluorescence quantum yields are good candidates for such purposes. The dyes can be chemically modified by long alkyl chains in order to convert them into amphiphiles and to make them suitable for spreading into insoluble Langmuir monolayers [6][7][8][9][10][11]. However the most monolayers made of pure amphiphilic rhodamine dyes have a poor stability and are hardly suited for the LB method.…”

Orientation and conformation of octadecyl rhodamine B in hybrid Langmuir–Blodgett monolayers containing clay minerals

“…5,8,[38][39][40] Studies of chromophores in monolayers prepared on water show tilted orientations. 15,17 Fig. 5 (a) UV-Vis absorption spectra and (b) calculated dimer spectra of RhB18-saponite films prepared on dispersions with increasing clay concentration deposited at a surface pressure of 2 mN m À1 .…”

“…The surfaces that have been investigated regarding the orientational organization comprise intercalation compounds (e.g., interlamellar regions of clay minerals, [3][4][5][6][7][8][9] K 4 Nb 6 O 17, 10 aluminium oxide 11 ) and flat substrates (e.g., external surfaces of clay minerals, 12,13 gold, 14 water, 15,16 glass/quartz [17][18][19][20] ). The orientation of dye molecules adsorbed on surfaces has been determined using one or a combination of the following techniques: X-ray diffraction, [5][6][7]9,10 polarized ultraviolet-visible (UV-Vis) spectroscopy, 6,10,12,17,19,20 fluorescence spectroscopy, 16 molecular modeling, 9 scanning tunneling microscopy, 14 second harmonic generation, 13,[15][16][17][18] near edge X-ray absorption fine structure spectroscopy 21 and polarized transmission infrared spectroscopy. [6][7][8] Smectite clay minerals are silicate materials that consist of ca.…”

Fluorescence Resonance Energy Transfer between organic dyes adsorbed onto nano-clay and Langmuir–Blodgett (LB) films

“…One can also observe significant increase in NK fluorescence intensity in clay dispersion. Blue shifting and increase in fluorescence intensity for other dyes in constrained media have been reported [25,26] and explained to be as the conformational change of the monomer is responsible for the redistribution of energy levels. But our later studies of fluorescence spectra e in clay dispersion the broad band at 472 nm may be an overlapping of both the monomer and Hband.…”