Two-Photon absorption study in fluorescent Benzothiadiazole derivatives: brightness magnitude determination

Abstract

The radiation-matter interaction is one of the relevant topics of study in physics due to the amount of information that can be obtained and interpreted. When this interaction is caused by high-intensity light, a non-linear response of this medium can be observed, which generates new optical effects, such as two-photon absorption, which can be applied in different technological areas. Therefore, materials that have high nonlinear optical effects are of great interest to the scientific community, as they can be used in biological markers. The spectroscopic characterizations of organic molecules involve obtaining linear and nonlinear optical properties through time-resolved or non-time-resolved techniques. These can be obtained by pulsed laser systems with a short time span, enabling the understanding of how molecules behave in the function of their structure with light intensity. This fact increased the understanding of multiphotonic absorption studies and their dependent effects, not observed in low-intensity spectroscopy measurements.In the specific case of organic compounds, the effort is focused on the search for chromophores capable of enhancing the intended optical phenomenon. In particular, the effects of fluorescence induced by multiphotonic absorption on organic compounds are important for applications as fluorescent biomarkers. The fact that these compounds absorb by two or more photons is important for the selectivity of the process. For example, multiphotonic absorption shifts the excitation window to the near-infrared region. Multiphotonic effects combined with the transparency region of biological systems (at near IR) have been used for photodynamic phototherapy (PDT) induced by multiphotonic absorption. In the same sense, this can be incorporated into biomarkers. Aiming at a possible application in fluorescent markers, this project intends to study the effect of two-photon absorption in fluorescent Benzothiadiazole derivatives, which can present a high or small fluorescence effect, depending on the solvent. These studies will be conducted specifically for nonlinear optical processes, such as two-photon absorption and the fluorescence induced by this process. As a result, it is expected the determination of the brightness property, which is defined by the product between the fluorescence quantum yield and the two-photon absorption cross-sections, is an important property to be quantified for applications in fluorescent probes. (AU)