Three-dimensional Molecular Orientation Research Articles

Precise orientation control of a liquid crystal organic semiconductor via anisotropic surface treatment

We report a three-dimensional (3D) molecular orientation control of a liquid crystal organic semiconductor (LC-OSC) based on the long-range ordering characteristic of an LC material. To this end, a synthetic LC-OSC molecule, MeOPh-BTBT-C8, with a fluidic nematic (N) phase that is essential for alignment control over a large area and a smectic E (SmE) phase showing high ordering, was prepared. A simple flipping of a sandwich cell made of the LC-OSC material between the top and bottom substrates that have uniaxial–planar degenerated alignment as well as crossed rubbing directions responds to the given surface anchoring condition and temperature gradient. Optical observation of the alignment-controlled LC-OSC was carried out by polarized optical microscopy (POM), and the corresponding charge carrier mobility was also measured by fabricating organic field-effect transistors (OFETs). Our platform offers a facile approach for multidirectional and multifunctional organic electronic devices using the stimulus–response characteristics of LC materials.

Three-Dimensional Molecular Orientation Imaging of a Semicrystalline Polymer Film under Shear Deformation

Three-Dimensional Molecular Orientation Imaging of a Semicrystalline Polymer Film under Shear Deformation

Fast determination of three-dimensional fibril orientation of type-I collagen via macroscopic chirality

Polarization-resolved second harmonic generation (SHG) microscopy is appealing for studying structural proteins and well-organized biophotonic nanostructures, due to its highly sensitized structural specificity. In recent years, it has been used to investigate the chiroptical effect, particularly SHG circular dichroism (SHG-CD) in biological tissues. Although SHG-CD attributed to macromolecular structures has been demonstrated, the corresponding quantitative analysis and interpretation on how SHG correlates with second-order susceptibility χ(2) under circularly polarized excitations remains unclear. In this study, we demonstrate a method based on macroscopic chirality to elucidate the correlation between SHG-CD and the orientation angle of the molecular structure. By exploiting this approach, three-dimensional (3D) molecular orientation of type-I collagen is revealed with only two cross polarized SHG images (i.e., interactions of left and right circular polarizations) without acquiring an image stack of varying polarization.

Laser-field-free three-dimensional molecular orientation

Laser-field-free three-dimensional orientation, corresponding to the complete control of spatial directions of asymmetric top molecules, is achieved with combined weak electrostatic and elliptically polarized laser fields with an 8-ns turnon and a 150-fs turnoff, which is shaped by a plasma shutter. Rotationally cold 3,4-dibromothiophene molecules are used as a sample, and their lower-lying rotational states are selected by a molecular deflector to increase the degrees of orientation. After the rapid turnoff of the pump pulse, higher degrees of orientation are maintained for 5--10 ps, which is long enough for various applications including electronic stereodynamics in molecules with femtosecond pulses.

Determination of 3D molecular orientation by concurrent polarization analysis of multiple Raman modes in broadband CARS spectroscopy.

A theoretical description is presented about a new analysis method to determine three-dimensional (3D) molecular orientation by concurrently analyzing multiple Raman polarization profiles. Conventional approaches to polarization Raman spectroscopy are based on single peaks, and their 2D-projected polarization profiles are limited in providing 3D orientational information. Our new method analyzes multiple Raman profiles acquired by a single polarization scanning measurement of broadband coherent anti-Stokes Raman scattering (BCARS). Because the analysis uses only dimensionless quantities, such as intensity ratios and phase difference between multiple profiles, the results are not affected by sample concentration and the system response function. We describe how to determine the 3D molecular orientation with the dimensionless observables by using two simplified model cases. In addition, we discuss the effect of orientational broadening on the polarization profiles in the two model cases. We find that in the presence of broadening we can still determine the mean 3D orientation angles and, furthermore, the degree of orientational broadening.

Controlling the Alignment and Orientation of Gaseous Molecules with Laser Electric Fields

Since most molecules are anisotropic quantum systems, alignment or orientation dependence called steric effects is ubiquitous nature in various phenomena where molecules are involved. Therefore, not only in stereodynamics of chemical reactions but also in electronic stereodynamics in molecules, alignment or orientation dependence is always a matter of central concern and the importance of molecular alignment and orientation techniques has been more and more rising. Here various molecular alignment and orientation techniques with intense nonresonant laser fields are reviewed mainly in chronological order. They include one- and three-dimensional molecular alignment both in the adiabatic regime and in the nonadiabatic regime, and one- and three-dimensional molecular orientation in the adiabatic regime. More recent progresses are the demonstrations of laser-field-free molecular orientation and all-optical molecular orientation. Finally future subjects and perspectives on the applications with a sample of aligned or oriented molecules are discussed.

T0302-2-3 立体配向顕微鏡を用いた非接触・非破壊歪み計測([T0302-2]高信頼マイクロ・ナノデバイスのための設計・計測技術(2):応力・ひずみ計測)

T0302-2-3 立体配向顕微鏡を用いた非接触・非破壊歪み計測([T0302-2]高信頼マイクロ・ナノデバイスのための設計・計測技術(2):応力・ひずみ計測)

Second-harmonic-generation microscope using eight-segment polarization-mode converter to observe three-dimensional molecular orientation: publisher's note

The order of authors in Opt. Lett.32, 1680 (2007) was incorrect as published. The order has been corrected online as of August 1, 2007.

Second-harmonic-generation microscope using eight-segment polarization-mode converter to observe three-dimensional molecular orientation

We developed a compact polarization-mode converter for microscopy to control three-dimensional polarization at the focus. The converter consisted of two homogeneously aligned liquid-crystal spatial light modulators with eight independently controllable electrodes (segments), and a quarter-waveplate. The converter converted a linearly polarized beam to three polarization modes: two orthogonal linear polarizations and a pseudo-radial polarization. We applied the converter to second-harmonic-generation microscopy and demonstrated the detection of three-dimensional molecular orientation.

Three-dimensional molecular orientation with combined electrostatic and elliptically polarized laser fields

We report an experimental demonstration of the three-dimensional orientation of gas-phase molecules by applying the combination of an electrostatic and an elliptically polarized laser field. Three-dimensional orientation was verified using a technique in which two-dimensional ion imaging and time-of-flight mass spectrometry are complementarily used.

Proposition of Single Molecular Orientation Determination Using polarization Controlled Beam by Liquid Crystal Spatial Light Modulators

We have proposed a method to control the three-dimensional electric field in the focus of an optical microscope using two non-twisted liquid crystal spatial light modulators, and to detect the molecular orientation of a single molecule. The three-dimensional electric field is generated by focusing the beam with two dimensional spatial distribution of polarization. The possibility of detection of three-dimensional single molecular orientation was shown by numerical calculations. © 2005 The Optical Society of Japan

Full tensor optical rheometry of polymer fluids

A novel three-dimensional flow birefringence technique has been developed to measure the real time, three-dimensional, optical anisotropy in flowing polymer solutions. Full tensor optical rheometry utilizes three polarization-modulated beams to probe all independent elements of the refractive index tensor and is, thus, used as a quantitative probe of time-dependent, three-dimensional average molecular orientation. We present results for shear flow of polystyrene in a 6% semidilute solution of tricresyl phosphate over a range of shear rates. Although the time-dependent behavior of N2 has not been widely reported, probably because of experimental difficulties, it can be a powerful means of testing rheological models. Experimental measurements of the transient behavior of N2 and −N2/N1 on inception and cessation of simple shear flow are compared with the predictions of the Doi–Edwards and Giesekus models. The Giesekus model is in qualitative agreement with most of the time-dependent features observed for N2 and −N2/N1. On-flow inception overshoots in N2 and −N2/N1 are observed. Further, on-flow cessation, N2 relaxes more slowly than N1 and −N2/N1 shows a strong nonexponential increase to a constant value of ∼0.9 at long times. The Doi–Edwards model is less successful in predicting transient results but agrees quite well with observed steady-state dependence of N2 with shear rate.