Observation of second-harmonic generation form Langmuir-Blodgett multilayers of a hemicyanine dye

Girling, I.R.; Cade, N.A.; Kolinsky, P.V.; Earls, J.D.; Cross, Graham H.; Peterson, I. R.

doi:10.1016/0040-6090(85)90462-6

Cited by 163 publications

(37 citation statements)

References 15 publications

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“…Experimental ODEP + Br ± was prepared following reported methods [8,12]. The polyelectrolytes used in the present study were poly(sodium 4-styrenesulfonate) ((Na :monomer unit of the polyanion~1:8), allowing equilibration for 120 min, and compressing at 50 cm 2 min ±1 (Nima Model 611M or USI Model FDS-23 LB trough was used).…”

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confidence: 99%

Laser‐Induced Second Harmonic Generation Decay in a Langmuir– Blodgett Film: Arresting by Polyelectrolyte Templating

et al. 2005

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Ultrathin films of amphiphilic molecules fabricated by the Langmuir±Blodgett (LB) technique form an important class of functional molecular materials and are promising candidates for molecular scale devices. A fundamental problem associated with LB films, which has limited their applications, is that once the molecular assembly obtained through mechanical compression of Langmuir films at the air±water interface is transferred to a solid substrate as an LB film, it is no longer necessarily in a thermodynamically stable state.[1] The LB film can undergo molecular-level reorganizations with or without external stimuli, [2±4] which can impair its potential functionality. [3,4] An interesting case in point is that of LB films based on quadratic nonlinear optical (NLO) chromophores, which exhibit second harmonic generation (SHG). The laser irradiation involved in the SHG process can itself perturb the molecular assembly in the film with detrimental consequences for its SHG capability. Demonstration of such a phenomenon and development of a suitable solution are of fundamental interest in the design of LB films. Amphiphiles based on the prototypical NLO-phore hemicyanine dye are usually in an aggregated state in Langmuir [5,6] and LB films, [7] causing the SHG from the latter to diminish or vanish altogether. [4,8±12] However, slow equilibration after spreading on the water surface was found to result in LB films with reduced aggregation and improved SHG. [12,13] We have now observed that such a film, apparently in a metastable state, exhibits a pronounced decay of SHG in successive measurements involving laser irradiation. The traditional solution to the problem of aggregation has been to admix the NLOphore-based amphiphile with molecules like fatty acids; [11] such an approach, however, leads to the dilution of the active molecule in the two-dimensional lattice and possibly phase separation. [10] We have shown that polyanions introduced in the subphase can dramatically improve the stability of a pyridinium-based Langmuir film. [14] It was also demonstrated that the SHG from LB films of the cationic hemicyanine dye is enhanced when the films are fabricated with polyanions in the subphase, due to deaggregation of the NLO-phores without dilution. [12,13] In this work, the polyelectrolyte methodology is shown to be an effective strategy to arrest SHG degradation in the hemicyanine LB film as well. Morphological features of the LB films observed by atomic force microscopy (AFM) reveal the impact of the polyelectrolyte. Electronic absorption studies provide insight into the molecular-level interactions that trigger the SHG decay. SHG from the monolayer LB films of N-n-octadecyl-4-[2-(4-dimethylaminophenyl)ethenyl]pyridinium bromide (ODEP + -Br ± ) was measured soon after deposition, allowing sufficient time for drying; details of the procedure may be found elsewhere. [12,15] The fringe recording takes about 13 min, during which time the sample is continuously irradiated. The measurements were repeated several times...

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Laser‐Induced Second Harmonic Generation Decay in a Langmuir– Blodgett Film: Arresting by Polyelectrolyte Templating

et al. 2005

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“…19 Z-type [19][20][21] and Ytype alternated multilayers 18 ' 22,23 have been studied; the corresponding SH signals increase with the number of active 20 quadratic, 19 or superquadratic 21 dependence, depending on the structure and the deposition conditions of the samples. Linear electro-optic effects of a monolayer of hemicyanine have also been demonstrated.…”

Section: _4mentioning

confidence: 99%

Second-harmonic generation in Langmuir–Blodgett monolayers of stilbazium salt and phenylhydrazone dyes

Lupo¹,

Praß

Scheunemann³

et al. 1988

J. Opt. Soc. Am. B

155

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“…[20,23] Monolayer LB films were fabricated on a Nima Model 611M LB trough. UV/Vis absorption spectra were recorded on a Cary 100 Bio UV/Vis or Jasco V-570 UV/Vis-NIR spectrometer.…”

Section: Odepmentioning

confidence: 99%

Assembly of Gold Nanoparticles on a Molecular Ultrathin Film: Tuning the Surface Plasmon Resonance

2010

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A number of methodologies for immobilizing metal nanoparticles in 2-dimensional aggregate structures on various substrates, some with concomitant tuning of the surface plasmon resonance (SPR), have been reported. Many of them involve special functionalization of the nanoparticles, multiple fabrication steps or lengthy procedures. The present study demonstrates that monolayer Langmuir-Blodgett (LB) film of a hemicyanine-based amphiphile with cationic headgroup is an easily fabricated platform for harnessing citrate-stabilized gold nanoparticles. It is shown that a single immersion step can be used to immobilize the nanoparticles uniformly on large area films and that systematic variation of the immersion time from 10 min to 6 h leads to controlled assembly of the particles and tuning of the SPR band over approximately 100 nm. A model for the structural reorganization in the LB film that facilitates the assembly of nanoparticles is presented and the advantages of the current methodology over earlier protocols are pointed out. The versatility of LB films in terms of the molecular level control of fabrication it enables and the variety of film structures that can be realized, point to the wide scope for future explorations, expanding upon the present observations.

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Observation of second-harmonic generation form Langmuir-Blodgett multilayers of a hemicyanine dye

Cited by 163 publications

References 15 publications

Laser‐Induced Second Harmonic Generation Decay in a Langmuir– Blodgett Film: Arresting by Polyelectrolyte Templating

Laser‐Induced Second Harmonic Generation Decay in a Langmuir– Blodgett Film: Arresting by Polyelectrolyte Templating

Second-harmonic generation in Langmuir–Blodgett monolayers of stilbazium salt and phenylhydrazone dyes

Assembly of Gold Nanoparticles on a Molecular Ultrathin Film: Tuning the Surface Plasmon Resonance

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