Time-resolved microscopic optical second-harmonic generation (TRM-SHG) technique provides a different approach to study the dynamics of carriers in organic field-effect transistor (OFET). Different from many common methods, the TRM SHG directly probes the transient electric-field distribution in the channel of the OFET in high temporal and spatial resolutions. In this work we used this technique to quantitatively study migration of the peak of the electric field. We found that under a broad range of experimental conditions, the migration of the peak of the electric field follows a diffusionlike behavior; namely, the square of the peak position of $\overline{x}$ is proportional to time $t$. Based on a two-dimensional computational simulation and general carrier transport mechanism, we proposed that this behavior arises from a simple relation, $\mu \simeq \gamma {\overline{x}}^2/\left(t\left|V_{\text{gs}}\right|\right)$, where $\mu$ is the carrier mobility, $\gamma$ is constant about 0.5, and $V_{\text{gs}}$ is the gate voltage with respect to the source voltage. The experimental and simulation data well supported this relationship.

The azobenzene-substituted diacetylene (NADA) LB films were fabricated and their chiroptical properties were investigated in detail. It was found that the NADA LB films showed supramolecular chirality, although the NADA molecule itself was achiral. Overcrowded packing of azobenzene chromophores were believed to be responsible for the supramolecular chirality formation of NADA LB films. When irradiated by left- and right-handed circular polarized ultra-violet light (CPUL), obviously opposite CD signals for azobenzene chromophores and polydiacetylene (PDA) chains were observed from the resulting polymerized NADA (PNADA) LB films. Reversible changes of CD signals for PDA chains could be observed in response to thermal stimulus. When irradiated by left- and right-handed circular polarized lasers (CPL, 442 nm), a reversible chiroptical switch between two enantiometric structures of PDA chains could be observed by alternating the stereoregular packing of azobenzene chromophores in the side chains. Strong collective non-covalent interactions (π–π stacking) and rapid conformational rearrangement of azobenzene chromophores under CPUL or CPL treatment were believed to be responsible for the supramolecular chirality formation and reversible chiroptical switches upon thermal and photic stimuli. This research provides a novel model system for understanding the detailed mechanism of the chiroptical introduction and modulation in the PDA backbone.

Herein, photo-controlled rearrangement of the azobenzene chromophore in the side chains was used to realize enantioselective polymerization and light-triggered reversible switching between opposite chirality for the PDA backbone.

The dielectric polarization of organic monolayers at the air–water interface has been analyzed, assuming that the monolayers have C∞ symmetry. The formula of polarization of organic monolayers is derived and it is expressed using orientational order parameters. It is shown that Maxwell-displacement current measurement coupled with optical second harmonic generation measurement is helpful for the determination of these orientational order parameters. Monolayers of 4′-n-pentyl-4-cyanobiphenyl on the air–water interface were examined during monolayer compression and the orientational order parameters were determined.

Expansion analysis shows that in second order, the weak boundary coupling of nematic liquid crystals should be depicted by two anchoring coefficients and an orthonormal vector triplet. Using this binomial anchoring energy, we have derived the analytical expression of the threshold and saturation properties of the twisted nematic effect and the homeotropic to twisted-planar transition. Our results prove clearly that these two quite different transitions are reverse effects of each other.