We have developed novel humidity and gas detector system using quartz crystal oscillators (QCO) deposited with cellulose Langmuir-Blodgett (LB) films. We have realized stable humidity detection by the LB-based QCO sensor for extremely high humidity subsequent to the water dipping condition. Also, specific gaseous molecules such as alcohol could have been sensitively detected.

The cationic dye, E-N-alkyl-4-[2-(4-alkyloxynaphthyl) ethenyl] quinolinium bromide has a wide-bodied chromophore with alkyl groups at opposite ends, i. e. CmH2m+1-D-π-A+-CnH2n+1 X-, where D and A are electron-donor and electron-acceptor groups respectively, π is a conjugated bridge and X- is the bromide counterion. It forms non-centrosymmetric Langmuir-Blodgett (LB) structures in which the packing is dependent upon the combination and compatibility of the alkyl groups. Films of two isomeric analogues where m + n = 34, have a layer thickness of 4.3 nm when the groups are significantly different (m = 12 and n = 22) which decreases to 2.5 nm when they are similar (m = 18 and n = 16). The latter adopts an interdigitating layer arrangement at both the upper and lower interfaces and it is the first example of a Lego-type structure with non-centrosymmetric alignment of the optically nonlinear chromophores. This is evidenced by the second-harmonic intensity, which increases quadratically with the number of layers, i. e. as .

Recent technologies of organic film devices are reviewed. New technologies of fabrication and characterization of organic thin films, electro-mechanical conversion materials, and applications for electrical and optical devices are discussed. In this review paper, especially organic light emitting diodes, tunneling junctions using polyimide Langmuir-Blodgett films, tunneling spectroscopy and high-density recording, plastic actuators using conducting polymers, molecular self-assembly process for fabricating organic thin film devices are reviewed.

We developed a measuring system that measures both capacitance and transmittance of a liquid crystal (LC) cell simultaneously. We then studied the dynamic orientation process of nematic LC molecules between two-photochromic command surfaces. The command surfaces consist of a polymer monolayer bearing azobenzene side chains and they are deposited on glass substrate coated with indium-tin-oxide by using the Langmuir-Blodgett technique. The capacitance of LC cells increased and decreased alternately due to orientation transition in LC molecules by irradiating ultraviolet (UV) and visible light, respectively. Similarly, with the alternating irradiation of UV and visible lights, the transmittance of the LC cell changed periodically. Mean tilt angles of LC molecules under irradiation of UV and visible lights were evaluated from the results of capacitance and transmittance. It was found that the transient transmittance response was delayed to the transient capacitance under the UV irradiation. This result corresponds to that the LC molecules in homeotropic mode tend to remain the optical alignment.

To investigate the effect of alkyl chain length and adsorption time on the charge-transfer complex formation, ultraviolet-visible absorption and inelastic electron tunneling (IET) spectroscopy measurements were carried out for the tetramethylphenylenediamine (TMPD; donor molecule) adsorbed dodecyl-, pentadecyl- and octadecyl-tetracyanoquinodimethane (TCNQ) Langmuir-Blodgett (LB) films. In the optical absorption spectra, the main peak of LB films shows a red-shift depending on alkyl chain length and adsorption time. Furthermore, the dependence on alkyl chain length and adsorption time are also shown in the IET spectra. These results demonstrate that adsorption LB methods enable to control the adsorption ratio of functional molecules and the CT complex formation.

Control of electronic states of dye molecules (organic semiconductors) by introducing appropriate substituent groups has been examined. NH2 (electron-releasing group) and NO2 (electron-withdrawing group) were introduced in thiacarbocyanine dye to modify the electronic states of the dyes. The effect of modification was examined based on the properties of photoelectric cells made by the dye derivatives. Clear increase in photocurrent, more than ten times, was observed when modified dyes were used instead of the original dye. The result shows that the introduction of substituent groups for organic semiconductors is quite effective to control the electronic states, and the introduction can be regarded as doping in molecular level.

We fabricated junctions with a porphyrin polyimide (PORPI) monolayer, and then investigated the electron transport properties of the junctions from the current-voltage (I-V) and d2V/dI2-V measurements. Polyimide LB films without porphyrin were used as tunneling barriers. One large peak was seen at a voltage around 1.9 V, due to the excitation of electron transitions in PORPI molecules, whereas a step structure was not observed in the I-V characteristic.