Spectroscopic Study of Nonamphiphilic 2,2‘-p-Phenylenebis(5-phenyloxazol) (POPOP) Assembled in Supramolecular Langmuir−Blodgett Films

Abstract

This paper reports the incorporation of a nonamphiphilic blue laser dye 2,2′-p-phenylenebis(5-phenyloxazol), abbreviated as POPOP, in Langmuir-Blodgett (LB) films mixed with stearic acid (SA) and their spectroscopic properties. The surface pressure versus area per molecule isotherms of POPOP mixed with SA at different molar ratios reveal a plateau-like region that suggests reorientation of the POPOP molecules from lying flat at the air-water interface to an almost vertical alignment. Miscibility studies indicate a repulsive type of interaction between the components in the mixture, resulting in the formation of microcrystallites in the LB films that is confirmed by spectroscopic studies. Perhaps the most interesting feature of this study is the appearance of a new band at about 400 nm in absorption spectra of the mixed LB film of POPOP and SA that is assigned to a low-lying hidden 1 L b state. The appearance of the same band in a mixture of ethanol and water with the volume fraction of water in the mixture exceeding 76% confirms that the manifestation of this band is aggregation induced. Fluorescence emission studies of POPOP in solution reveal a structured emission that originates from the 1 L a state, while the emission studies from the LB films exhibit two bands, one at 420 nm originating from the low-lying 1 L b state of the monomer and the other at 460 nm corresponding to a 1 L b dimer. Excitation and polarized anisotropy measurements confirm these findings and indicate that the above observations may be attributed to a deformed geometry of the POPOP molecules in the LB films.

Photophysical characterizations of 2-(4-biphenylyl)-5 phenyl-1,3,4-oxadiazole in restricted geometry

“…It is interesting to note that the spectroscopic and aggregation behaviour of non-amphiphilic blue laser dye 2, 2 0 -p-phenylene bis (5-phenyl oxazol) (POPOP) on the restricted geometry of LB films have been reported by Dutta [14]. Spectroscopic analysis confirms the formation of microcrystallites of POPOP in the LB films.…”

“…Non-amphiphilic molecules are not ideally suited for thin film deposition by this technique. However, some recent works [10][11][12][13][14][15][16][17] showed that highly organized LB films of these materials can be formed, when a long-chain fatty acid or some inert polymer matrix was used as the supporting medium. Since these non-amphiphilic molecules are easily available and have wide varieties having different interesting physical properties, hence a lot of investigations on LB films using these molecules are necessary.…”

Fluorescencing behavior of thin solid films based on polyelectrolyte‐surfactant complex and dye molecules

“…30 Monolayers of nonamphiphilic molecules are instable and cannot be transferred onto solid substrates. 30 Monolayers of nonamphiphilic molecules are instable and cannot be transferred onto solid substrates.…”

“…It is known that for nonamphiphilic dyes that are insoluble in water, e.g., for oxazines dyes, it is possible to record a isotherm of monolayer compression on phase interface. 30 Monolayers of nonamphiphilic molecules are instable and cannot be transferred onto solid substrates. 6,30 It was observed (Figure 3, curve 2) that pure NR at the air-water interface does not form stable monolayer and surface pressure rise from an initial ''zero'' value to about 20 mN m À1 .…”

Photoluminescence properties of polystyrene-hosted fluorophore thin films

“…All these fluors have high absolute photoluminescence (PL) yields. 4,[10][11][12] The solvatochromic characteristics of these fluors have been studied comprehensively in different non-polar and polar solvents, solid solvents such as thin-films, different polymer environments and in thin-films. 2,10-15 Coumarin 6 is a benzopyrone-class dye with a dialkyl-substituted amino-group and a benzothiazole-group asymmetrically placed around a lactone-ring.…”