Application of spectroscopy and super-resolution microscopy: Excited state dynamics of relevant fluorescent dyes and nano-materials, characterization of solar cell materials and diagnosis of neuro-degenerative disease

Photophysics of inorganic materials and organic molecules in complex biological systems and in commercially important materials have been widely studied with absorption and emission spectroscopy. Excited-state properties of fluorophores have been elucidated by steady-state and time-resolved fluorescence studies. Time-resolved fluorescence measurements are generally richer with information about excited-state properties and the environment in the vicinity of the fluorophore than steady-state measurements despite the more extensive use of the later in analytical studies. Throughout the thesis different photophysical studies on systems such as, highly stable fluorescent probes, nano-materials, photovoltaics and infected animal tissues have been discussed. Photoinduced electron transfer between fluorophores used in super-resolution microscopies and amino acids or nano-materials systems have been characterized. These findings can provide better understanding of the properties of different nanomaterials or can help to understand lifetime images of these dyes in biological systems. In addition to spectroscopy, microscopic measurements are very informative; particularly, super-resolution microscopies such as stimulated emission depletion (STED) microscopy can provide us with different properties such as excited-state lifetimes, diffusion etc. with very high resolution. Here we discussed STED experiments on nano-materials and also explored a combination of STED and fluorescence correlation spectroscopy as a possible tool for observing nano-scale heterogeneities in two-dimensional systems. Thirdly, use of fluorescence spectroscopy as an analytical tool for screening of animals with transmissible spongiform disease has been examined. This findings can lead to non-invasive detection of the neurodegenerative diseases. Last but not the least, the fluorescence and absorption based techniques have also been used to characterize different solar cell materials. Here we addressed issues like ordering of polymers, photo-stability, excited-state properties of photovoltaic materials like P3HT and perovskites. The wide range of applications of optical spectroscopies have been investigated under a goal of better understanding of the fundamental processes and using them towards improving existing methods and materials of practical utility.