Optical Activity and Order in Luminescent Langmuir-Blodgett Poly(ρ-Phenylene Vinylene) Films

1999 ◽  
Vol 560 ◽  
Author(s):  
A. Marletta ◽  
F.E.G. Guimãraes ◽  
D. Gonçalves ◽  
P.T. Campana ◽  
O.R. Nascimento ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Optical Activity ◽  
Phenylene Vinylene ◽  
Layer By Layer ◽  
Interchain Interaction ◽  
Lb Films ◽  
Chain Orientation ◽  
Langmuir Blodgett ◽  
High Degree ◽  
Circular Dichroïsm

ABSTRACTLangmuir-Blodgett (LB) PPV films of poly(ρ-phenylene vinylene) (PPV) have been obtained using a mixture of a PPV precursor, poly(xylylidene tetrahydrothiophenium chloride) (PTHT), with the sodium salt of dodecylsulfonic acid (DBSA) as the spreading solution. Spincoated films were prepared in order to compare their properties with those of LB films. A large circular dichroism was observed for LB films but not for spin-coated ones. Optical activity of PPV films was characterized by circular dichroism technique, while optical properties were evaluated by optical absorption and luminescence measurements at various temperatures. Overall, the results obtained allowed us to conclude that the layer-by-layer LB process yields a high degree of molecular order in the PPV films with low interchain interaction. Polarized absorption and circular dichroism measurements demonstrate a preferential chain orientation along the dipping direction in the LB processing. The origin of the CD in the PPV-LB can be ascribed to convenient packing of individual monolayers given by the Z-type deposition.

Optical anisotropy and sign reversal in layer-by-layer assembled films from chiral nanoparticles

2016 ◽  
Vol 191 ◽  
pp. 141-157 ◽  
Author(s):  
Zhumei Liang ◽  
Kalil Bernardino ◽  
Jishu Han ◽  
Yunlong Zhou ◽  
Kai Sun ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Optical Activity ◽  
Metallic Nanoparticles ◽  
Density Functional ◽  
Structural Changes ◽  
Building Blocks ◽  
Layer By Layer ◽  
Semiconductor Films ◽  
Surface Ligands ◽  
Circular Dichroïsm

Chiral anisotropy and related optical effects at the nanoscale represent some of the most dynamic areas of nanomaterials today. Translation of optical activity of chiral semiconductor and metallic nanoparticles (NPs) into optoelectronic devices requires preparation of thin films from chiral NPs on both flat and curved surfaces. In this paper we demonstrate that chiral NP films can be made via layer-by-layer assembly (LBL) using negatively charged chiral CdS NPs, stabilized by d- and l-cysteine and positively charged polyelectrolytes, as building blocks. LBL coatings from NPs combine simplicity of preparation and strong optical activity. Circular extinction measurements using circular dichroism instruments indicate that the film possess four chiroptical bands at 280, 320, 350, and 390 nm. The latter two bands at 390 and 350 nm are associated with the band gap transitions (chiral excitons), while the former two are attributed to transitions involving surface ligands. When NPs are assembled in LBL films, the rotatory activity and the sign for circular extinction associated with the electronic transition in the inorganic core of the NPs is conserved. However, this is not true for circular extinction bands at short wavelengths: the sign of the rotatory optical activity is reversed. This effect is attributed to the change of the conformation of surface ligands in the polyelectrolyte matrix, which was confirmed both by semi-empirical and density functional (DFT) quantum mechanical calculations. Circular dichroism spectra calculated using a DFT algorithm closely match the experimental spectra of CdS NPs. These findings indicate that the spectroscopic methods sensitive to chirality of the surface ligands can be used to investigate fine structural changes in the surface layer of nanocolloids. Strong rotatory optical activity of nanostructured semiconductor films opens the possibilities for new polarization-based optical devices.

Induced optical activity (circular dichroism) of antibody-hapten complexes

1971 ◽  
Vol 1 (1) ◽  
pp. 67-82 ◽  
Author(s):  
John H. Rockey ◽  
Keith J. Dorrington ◽  
Paul C. Montgomery
Keyword(s):  
Circular Dichroism ◽  
Optical Activity ◽  
Circular Dichroïsm ◽  
Induced Optical Activity
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