Propriedades ópticas de sistemas orgânicos com características multifuncionais

Abstract

The present study is devoted to the investigation of photoluminescent organic materials which are sensitive to environment conditions, envisaging their use in sensing and imaging applications. Four different systems are investigated: a dithienylpyrrole derivative bearing a fluorene substituent (SNSFCA), a carbon quantum dot obtained from dansyl chloride (CD-DsCl), a carbon quantum dot synthetized from an azodye (CDMR), and a polymeric composite of polyvinyl alcohol (PVA) and a carbon dot. Using steady-state and transient UV-vis spectroscopy, we show that SNSFCA diluted in chloroform undegoes a photopolymerization under photoexcitation, which is characterized by changes in the physical parameters of photoluminescent mechanism. Concerning the study of carbon dots derived from dansyl chloride, it is analyzed how the environment conditions affect the photoluminescence of CD-DsCl, with emphasis on temperature and pH effects. Our results reveal that CD-DsCl exhibits a thermally-actived delayed fluorescence, which is associated with a reverse intersystem crossing due to the small energy gap between singlete and triplet excited states. The occurrence of an intersystem crossing in CD-DsCl is exploited to analyze the generation of reactive oxygen species (ROS) of such nanoparticles. Envisaging the use of dye effluents as carbon precursors, we also study the synthesis of carbon dots from the methyl red azodye (CDMR). Using a hydrothermal synthesis method, we have obtained highly nitrogen-doped carbon dots, which present excitation-dependent emission and thermal-quenching fluorescence behavior. Using flurescence confocal microscopy, the possibility of use CDMR in bioimaging application is analyzed, considering HeLa cells as the biological probe. Furthermore, we study the effects of CDMR addition on the optical properties of PVA films. From time-resolved Z-scan measurements, we investigate how the CDMR concentration affects the thermal-optic coefficient and thermal diffusivity of poymeric films. The effects of polymeric matrix on the fluorescence properties of CDMR are also investigated.