Polymer matrix dependence of conformational dynamics within a π-stacked perylenediimide dimer and trimer revealed by single molecule fluorescence spectroscopy

Abstract

The conformation of embedded molecule in a polymer matrix is sensitive to the local nano-environment that the molecule experiences. Particularly, single molecule spectroscopic methods have been utilized to visualize each molecular conformation in local sites of the polymer matrix by monitoring rotational diffusion and fluctuating fluorescence of the molecule. Here, we have performed single molecule spectroscopic experiments on a π-stacked perylenediimide (PDI) dimer and trimer, in which enhanced π-π interaction in π-stacked PDIs makes the fluorescence lifetime longer, embedded in two different polymers, namely poly(methyl methacrylate) (PMMA) and poly(butyl methacrylate) (PBMA), to reveal the conformational change depending on the polymer matrix. The fluorescence lifetimes of π-stacked PDIs are influenced by polymer surroundings because their molecular conformations are dependent on their interactions with the local environment in the polymer matrix. Furthermore, from an in-depth analysis of autocorrelation functions of fluorescence intensity trajectories, we could assign that the first autocorrelation value (lag 1) is larger as the intensity trace becomes more fluctuating. Thus, we expect that π-stacked PDIs, a model system for the formation of PDI excimer-like states, can be utilized to probe the surrounding nano-environment by monitoring the conformational change in real time.

Improving the Quantum Yields of Perylene Diimide Aggregates by Increasing Molecular Hydrophobicity in Polar Media

“…The traces could only be fit to a triexponential decay. Multiple components of the decay in these systems indicate that there are conformational inhomogeneities within the particles . The faster decay component with a sub‐nanosecond time constant is also observed in these systems.…”

“…An increase in the Huang‐Rhys factors can also improve H‐type aggregate emission . Small changes in the intermolecular interactions will affect the symmetry and, therefore, the quantum yield of these systems . The increase in solvent polarity will increase molecular confinement, which minimizes relaxation pathways in the aggregates.…”

“…The lifetime is very close to 20 ns, which indicates that the optically excited species are dimers. If the B13 formed larger aggregates or interacted strongly with the environment, the fluorescence lifetimes would be longer . The second decay pathway is significantly minimized as the water content in solution increases.…”

Photoluminescence Intermittency from Single Quantum Dots to Organic Molecules: Emerging Themes

“…Measured lifetimes of PDI were different for dimers and trimers dissolved in poly (butyl methacrylate) (PBMA) and PMMA polymers. Since PBMA has a large nonpolar side group that hinders chain packing, more free volume is available in this polymer allowing for changes in dimer orientation [120]. Other examples of environmental effects include butadiyene linked porphyrin dimers incorporated into PMMA of different percent weights [121].…”

π-Conjugated polymer-layered structures: synthesis and self-assembly

“…24,25 Among the different types of linkers, hairpin-shaped rigid linkers can promote the formation of intramolecular π-stacked structures. [26][27][28][29][30] We have recently reported the synthesis of polymers with layered aromatic rings using a xanthene scaffold as a hairpin-shaped linker; these polymers exhibit intramolecular π-stacked structures with multiple aromatic rings stacked along a single polymer chain. [31][32][33][34][35][36] They can be regarded as the assembly of several small π-conjugated units.…”