Fluorescence microscopy, a versatile tool to unravel polymer properties

Optical microscopy has revolutionized the way we understand our world and has become a crucial tool in a range of disciplines such as biology, physics, chemistry, and material sciences. The development of new microscopy techniques has been capital to its success and wide applicability. A prominent example is the recent development of methods that allow imaging in three dimensions. This has been a breakthrough in biology as scientists realized how important the 3D context is for cells and bacteria. However, in material sciences, the 3D context is not always as important, and thus, it is often more informative to use different parameters such as lifetime (x,y,τ) or excitation wavelength (x,y,λ) as additional “dimensions” to the measurement instead of the classical spatial dimensions. In this thesis, we develop multi-dimensional imaging methods and demonstrate their application in different areas of materials sciences. First, we use multiplane microscopy to do single particle tracking in 3D (x,y,z,t) to provide insight into optical trapping and the assembling of nanoparticles. We show that the inhomogeneous field of the optical trapping laser when tightly focused has a huge influence on the trajectories of the nanoparticles. For instance, it induces the formation of a metastable trapping position and the appearance of helicoidal trajectories. In addition, we show evidence of optical binding outside the irradiated area as the mechanism for the gold nanoparticle assembling under optical trapping. The second method is a correlation-based imaging technique (x,y,r) which was developed to analyse the blinking phenomenon in hybrid halide perovskite film. We show that we can map out the different regions of a film that blink differently. Moreover, by comparing with SEM images, we discovered that these regions correspond to individual grains in the film. This method paves the way to understand non-radiative decay in metal halide Perovskite semiconductors and provides a new type of imaging contrast. Finally, an excitation-emission microscope (x,y,λexc,λem) setup was used to study the structure-property relationships in the conjugated polymer TQ1 by measuring the 2D fluorescence spectra (excitation, emission) of individual molecules. We find that the excitation spectrum of a single chain is broad with a width similar to the corresponding polymer film while the emission spectrum is narrow. This confirms the idea that all the spectroscopic units of the chain absorb while only 1 or a few units contribute to the emission due to efficient intrachain energy transfer. This thesis demonstrates the potential and versatility of multi-dimensional imaging to investigate materials at the nanoscale.