The chemical synthesis and physicochemical and luminescent characterizations of polymers based on 3-HT, EDOT, and 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl) bisthiophene (fluorene) or (E)-2-(ethyl(4-((4-nitrophenyl)diazenyl)phenyl)amino)ethyl 2-(thiophen-3-yl)acetate (TDR1) are reported. The fluorene unit was bound to the conjugate backbone, while the Disperse Red 1 (DR1) chromophore was present as a pendant group. Characterizations by 1H NMR, FT-IR, DSC-TGA, GPC, UV-vis, cyclic voltammetry, fluorescence quantum yield, excited state lifetime, and two-photon absorption cross-section were carried out. These polymers combined the physicochemical properties of EDOT and 3-HT, such as high electron density, high charge mobility, low oxidation potential, and good processability. The optical properties of these copolymers were highly dependent on the presence of EDOT, the molecular weight, and the regioregularity rather than the presence of the third component (fluorene or TDR1). The good nonlinear absorption and luminescent properties exhibited by these copolymers were exploited to fabricate nanoparticles used as fluorescent tags for the imaging of microstructures.

Behavior of the photoacoustic signal produced by nanoparticles as a function of their concentration was studied in detail. As the concentration of nanoparticles is increased in a sample, the peak-to-peak photoacoustic amplitude increases linearly up to a certain value, after which an asymptotic saturated behavior is observed. To elucidate the mechanisms responsible for these observations, we evaluate the effects of nanoparticles concentration, the optical attenuation and the effects of heat propagation from nano-sources to their surroundings. We found that the saturation effect of the photoacoustic signal as a function the concentration of nanoparticles is explained by a combination of two different mechanisms. As has been suggested previously, but not modeled correctly, the most important mechanism is attributed to optical attenuation. The second mechanism is due to an interference destructive process attributed to the superimposition of the photoacoustic amplitudes generated for each nanoparticle, this explanation is reinforced through our experimental and simulations results; based on this, it is found that the linear behavior of the photoacoustic amplitude could be restricted to optical densities ≤ 0.5.In recent years, pulsed laser-induced ultrasound (US), better known as the Photoacoustic (PA) effect, has had a major resurgence because its wide range of applications, mainly in the biological and medical areas 1 , for instance, PA imaging 2 and as monitoring method in thermo-therapy of cancer 3 . Further the analogies between optical and acoustic phenomena, led to advancements in confocal PA microscopy 4 , creations of new methodologies to detect US 5 and generation of new materials to achieve thermal and/or acoustic contrasts 6 . PA effect is produced by the absorption of CW modulated pulsed optical radiation by a medium. This absorption raises non-radiative decays that increase the temperature and causes mechanical waves typically in the range of US. The major advantages for PA techniques are their sensibility to distinguish different optical contrast and the US penetration in the tissue 7 .Nowadays metallic nanoparticles (NPs) play an important role as enhancers of the PA signal, the design and application of these materials is subject to the type of applications desired, as well as to the available laser source.

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