In this work, two perylene derivatives containing different peripheral alkyl chains (i.e., N,N'-bis-(hexyl)perylene-3,4,9,10-tetracarboxyldiimide (ES-PTCDI) and N,N'-bis-(2'-ethylhexyl)perylene-3,4,9,10-tetracarboxyldiimide (EE-PTCDI)) were synthesized and efficiently dispersed at low loadings (from 0.01 to 0.1 wt %) into linear low-density polyethylene (LLDPE) by processing in the melt. Spectroscopic investigations (UV-vis and fluorescence) combined with quantum-mechanical studies demonstrated the ability of both chromophores to generate aggregates among the planar structure of dyes when dissolved in solution or dispersed into LLDPE above a certain concentration. The data acquired for dyes' dispersions into the polymer matrix reveal that the optical properties and responsiveness to mechanical stimuli are strongly dependent on the compactness of perylene aggregates provided by the different molecular structure of dyes. In particular, the strong intermolecular aggregates of ES-PTCDI resulted in being more resistant toward mechanical stress and less orientable by uniaxial drawing along the drawing direction of the film, whereas the less compact and distorted supramolecular architecture of EE-PTCDI chromophores provided composite films with a remarkable optical response to mechanical solicitations.

In this work, a water soluble perylene derivative containing piperazine peripheral units, i.e. N,N'-bis(2-(1-piperazino)ethyl)-3,4,9,10-perylenetetracarboxylic acid diimide dichloride (PZPER) was synthesized and dispersed at low loadings (from 0.1 to 1.1 wt%) into vinyl alcohol-containing polymer matrices. From the data acquired, the most effective driving force for the formation of intramolecular aggregates of PZPER was attributed to hydrogen bonding interactions. In particular, the aggregation extent was affected by the reduction of molecular interactions occurring in both solution and in polymer dispersions due to the decreasing polarity of the chromophore environment or increasing temperature. The sensitivity of PZPER aggregates dispersed into vinyl alcohol-containing polymer matrices towards mechanical stress was also reported. The responsiveness of PZPER optical properties (both in absorption and in emission) versus thermal or mechanical solicitations suggests applications of polymer dispersions as smart indicators to external stimuli.

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Polymer films with optical properties as indicators to thermal stress were obtained through the controlled dispersion of moderate amounts (0.1 wt.-%) of the 4,40-bis(2-benzoxazolyl)- stilbene (BBS) dye into a new semicrystalline ethylene-norbornene (E-co-N, N content of 15.3 mol.-%) copolymer characterized by a glass transition temperature (Tg) of about 64 8C. All the pristine films showed optical characteristics com- ing from noninteracting BBS chromophores. In contrast permanent optical changes were detected after film annealing at a T Tg due to the variation of the BBS supramolecular structure. The easy modulation of the optical features of polymer films by thermal perturbations suggests applications as threshold temperature visual indicators in thermoplastic materials

Linear low density polyethylene (LLDPE) films containing different concentrations of perylene (P) chromophores have been prepared by solution-casting and compression-moulding. The light emission features of the films depend on P concentration and polymer films deformation. A well-defined band attributed to the formation of micro/ nano-structured perylene chromophoric aggregates is observed with more than 0.1 wt.% of P in the film. The occurrence of this phenomenon changed the emission colour of the films from a bright blue (non- interacting dyes) to low intense pale yellow (interacting dyes) colour. During film drawing the LLDPE macromolecules reorganization is able to break the P supramolecular organization, leading to the prevalence of the blue emission of monomeric P. The optical behaviour of perylene dyes acting as internal stress- strain luminescent indicators for polyethylene films, provides a powerful tool to detect macromolecular organization