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Molecularly designed materials based on macromolecules and organic dyes offer unique opportunities in connection with the possibility of preparing optically responsive 'smart' materials. Indeed macromolecules are able to transmit and amplify small signals reaching sites at interacting distance through the involvement of the whole chain. The corresponding materials can then acquire stimuli-responsive properties in relation to specific features connected to primary structure and conformation. As a first approach to benefit from the above features for preparing eco compatible smartmaterials, bio-related polypeptides, polysaccharides and polyesters can be used as the macromolecular partner in combination with a selected dye following different interaction methodologies. Two distinct routes were used to prepare optically responsive products from the above bio-related polymers, respectively based either on the covalent bonding to the original macromolecules of photochromic molecular species, such as azobenzene and spiropyran, or on the morphology-modulated dispersion of highly conjugated dyes in the polymer bulk. Examples related to the two different routes have been investigated in our laboratory and are presented and discussed also with reference to selected recent cases from the literature.

A derivative of 2-methylindole, 3-[2-(4-nitrophenyl)ethenyl]-1-allyl-2-methylindole, NPEMI-A, is studied for its photoconductivity and photorefractivity behaviour. Its blends with the organic polymer poly-(2,3-dimethyl-N-vinylindole), PVDMI, are also investigated. Due to the expected and devised mutual solubility of the two components of the blends, it is possible to carry out measurements with the weight percent of the chromophore NPEMI-A changing from zero to 100. Films were produced by a squeezing process between two ITO-covered glass sheets. No opacity phenomena, that are so common for many other organic blends due to the segregation of the dissolved chromophore, are observed. The photorefractive optical gain Gamma(2) is obtained as a function of the chromophore content. Differential scanning calorimetry measurements (DSC) are also carried out to obtain the whole change of the glass transition temperature T(g) as a function of the amount of chromophore contained in the blends. From the experimental trend of T(g) a meaningful quantitative estimate of the value of the electrostatic interactions acting in the studied blends, is obtained. The importance of the value of T(g), and of the electrostatic interactions, in determining the extent of the photorefractivity is clearly evident. The results are compared for NPEMI-A (Gamma(2) = 210 cm(-1)) and for NPEMI-E (Gamma(2) approximately = 2000 cm(-1)) that has a N-2-ethylhexyl group instead of a N-allyl group. The Pockels and Kerr contributions and--for the first time--a "collaborative effect" of the photorefractivity of NPEMI-A are distinguished and quantitatively evaluated.

A derivative of 2-methylindole, 3-[2-(4-nitrophenyl)ethenyl]-1-allyl-2-methylindole, NPEMI-A, has been studied for its photoconductivity and photorefractivity behaviour. The neat material was studied together with its blends with the organic polymer poly-(2,3-dimethyl-N-vinylindole), PVDMI. It was possible to carry out measurements with the content of the chromophore NPEMI-A changing from zero to 100 wt. %. No opacity hint was observed. The photorefractive optical gain Γ2 was obtained as a function of the chromophore content inside the different films. Differential Scanning Calorimetry measurements (DSC) were also carried out to obtain the whole change of the glass transition temperature Tg as a function of the amount of chromophore contained in the blends. From the experimental trend of Tg it was possible to gather a meaningful quantitative estimate of the value of the electrostatic interactions inside the blends. The importance of the value of Tg, and hence of the electrostatic interactions, in determining the extent of the photorefractivity has been clearly put in evidence. This was done by comparing the results obtained for NPEMI-A (Γ2 = 210.1 cm−1) with other ones previously discussed for a molecule similar to NPEMI-A but having a 2-ethylhexyl group, NPEMI-E (Γ2 = 2,027 cm−1), instead of an allyl group. Three different contributions to the photorefractivity of NPEMI-A, namely the Pockels, the Kerr and the Collaborative ones, could be distinguished from the peculiar trend of Γ2 as a function of the composition of the blends.

In this work we present controlled, low-damage nanotopographic surface modification of poly(ethylene terephthalate) (PET). High-resolution nanopatterning over macroscopic areas was performed by 'low-temperature' hot embossing lithography (HEL). While for standard HEL the temperature is typically raised up to many tens of Celsius degrees above the polymer glass transition temperature (T-g), we demonstrate optimal results at a temperature very close to the bulk T-g of PET (72 degrees C). Nanopits and nanobarcodes were transferred onto the surface of PET commercial sheets, demonstrating reliable sub-100 nm resolution over macroscopic areas. Sample optical, mechanical, and thermal characteristics were systematically analyzed before and after embossing at low (75 degrees C) and high (150 degrees C) temperature by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, tensile tests, and differential scanning calorimetry (DSC). We show that, while conventional high-temperature HEL can lead to dramatic degradation of the polymer in terms of transparency, flexibility, and crystallinity content, our low-temperature process fully maintains original surface and bulk substrate properties.

The photorefractivity of an indole derivative and of its polymer blends has been studied at room temperature. The indole derivative 3-[2-(4-nitrophenyl)ethenyl]-1-(2-ethylhexyl)-2-methylindole (NPEMI-E) is a typical low-molecular-weight glass-forming molecule having peculiar nonlinear optics characteristics. It is unconditionally soluble in the photoconductive poly-(N-vinyl-2,3-dimethylindole) so that all the possible blends can be studied for a weight percent (wt. %) content of NPEMI-E ranging from zero to 100. A very high and sharp maximum of the photorefractive optical gain Gamma(2) approximate to 2000 cm(-1) was obtained for a NPEMI-E wt. % content of about 90. On the basis of recently published theoretical calculations, we have made the hypothesis that the rapid change of Gamma(2) can also be ascribed to a correspondingly quick variation of the molecular electro-optic parameters of the dissolved chromophore for some well distinguished values of its concentration in the polymer matrix. Differential scanning calorimetry measurements were made and the results carefully analyzed with the aim of obtaining information on the intermolecular interactions. These last measurements also allowed rationalizing the unconditionally stable glass appearance of the obtained blends. Measurements of spectroscopic ellipsometry were also made on blends with different NPEMI-E content. (C) 2008 Optical Society of America

The asymmetric two-beam coupling technique has been employed to measure the photorefractivity of thin films of polymer blends containing 2,5-dimethyl-4-(p-nitrophenylazo)anisole as the nonlinear optical component. Poly-(1-vinylindole) and poly-(2,3-dimethyl-1-vinylindole) were the photoconductive polymer counterparts. The values of the photorefractivity are reported. It appears that they are comparable with those of similar blends based on the well-known poly-(9-vinylcarbazole) (PVK), here considered as a reference standard. Careful differential scanning calorimetry analyses have been accomplished on the different blends taken into account to rationalize the significantly longer shelf lifetime of the indolyl-based films with respect to the PVK-based blends.