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Thermochromic transitions of the polydiacetylenes (PDAs) of the bis(ethyl)-and bis-(isopropyl)urethanes of 5,7-dodecadiyne-1,12-diol (poly(ETCD) and poly(IPUDO)) were investigated by solid-state 13 C cross-polarization and magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy and differential scanning calorimetry (DSC). Side group conformational changes resulting from the polymerization and thermochromic transition were monitored by solid-state 13 C CP/MAS NMR. Consecutive heating/cooling cycles in DSC experiments in the temperature range that includes the thermochromic transition reveal that poly(IPUDO) displays better reversibility than poly(ETCD). In solidstate 13 C CP/MAS NMR spectra, poly(IPUDO) showed more restricted side group movement during the transition than poly(ETCD), which may be the major factor for better reversibility. A nonthermochromic form of poly(ETCD) was prepared and compared to its thermochromic counterpart by means of X-ray powder diffraction, DSC, Fourier transform infrared spectroscopy (FT-IR), and solid-state 13 C CP/MAS NMR spectroscopy. Nonthermochromic poly(ETCD) maintains intramolecular hydrogen bonding between neighboring urethane functions as in thermochromic poly(ETCD). The 13 C NMR chemical shifts, sensitive to mechanical strain, of nonthermochromic poly(ETCD) showed an upfield shift of 2 ppm from the red phase alkyne carbon resonance of thermochromic poly(ETCD), which may be an indicator of the removal of thermochromic interactions.

An epoxy based polymer with nonlinear optical azo chromophores was designed to contain anionic groups to induce water solubility and self assembly. Using this polyanion with a polycation, multilayers were prepared on a glass substrate by alternating adsorption from dilute aqueous solutions. The azo chromophores in the confined layer of the polyanion in the multilayer films self-assemble into a noncentrosymmetric alignment and demonstrate second order optical nonlinearity (d33 = 19 pm/V).

Metal/Langmuir–Blodgett monolayer/metal devices, where the monolayer consists of the dodecyloxyphenylcarbamate of 2-bromo, 5(2′-hydroxyethoxy) tetracyanoquinodimethan, a donor-σ-acceptor molecular system, have been constructed, and dc current-voltage (I-V) characteristics of these devices were recorded at room temperature. For biases of ±20 mV, the I-V characteristics are linear, changing to a nonlinear form for higher voltages. This nonlinear characteristic exhibited a ln(I)∝V1/4 dependence for both positive and negative voltages up to ±1 V. For positive voltages >+2.0 V for as-prepared devices and >+1.5 V for annealed devices, a ln(I)∝V3 dependence was observed, revealing a very large increase in current for small voltage changes. Such behavior was not observed for corresponding negative voltages, indicating rectification across a distance approximated by the length of an individual molecule.

Both ac and dc conduction processes through thin Langmuir–Blodgett (LB) films of the dodecyloxyphenylurethane of 2-bromo-5 (2′-hydroxyethoxy) tetracyanoquinodimethan (DDOP-C-TCNQ, a redox-active molecule) sandwiched between dissimilar metal (Pt and Mg) electrodes have been studied. The dc conduction changed from a linear I/V characteristic for the lowest applied voltages (±20 mV) to a symmetric nonlinear characteristic obeying a ln I∝V1/4 dependence for voltages up to ±1.5 V, in as-prepared samples. For larger positive voltages, a large increase in current was observed with the dependence changing to a ln I∝V3 law, a dependence not reported previously for metal/LB film/metal systems. For increased negative voltages, the ln I∝V1/4 was again observed. For low applied ac fields, the conductance was found to follow a ωn law with a value of n close to 0.8. The effect of heat annealing the samples was also studied with significant differences in the observed changes in conductance between bilayer and monolayer structures. Emphasis was placed on understanding the conduction process through the single DDOP-C-BHTCNQ layer film. For the monolayer device, hysteresis is observed in the positive bias, and both as-prepared and annealed samples exhibit ln I∝V3 behavior. Such behavior was not observed for the corresponding negative voltages, indicating rectification across a distance approximated by the length of an individual molecule. Possible models of the three-dimensional arrays for both monolayer and multilayer metal/LB film/Mg structures are presented. The weight of existing experimental results does not support the Aviram–Ratner ‘‘molecular rectifier’’ concept for presently known Pt/LB monolayer/Mg devices.

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