Supramolecular self-assembly
of small organic molecules has emerged as a powerful tool to construct
well-defined micro- and nanoarchitecture through fine-tuning a range of
intermolecular interactions. The size, shape, and optical properties of these
nanostructures largely depend on the temperature and polarity of the medium,
along with the specific self-assembled pattern of molecular building units. The
engineering of supramolecular self-assembled nanostructures with morphology-dependent tunable emission is in high demand due to the
promising scope in nanodevices and molecular machines. However, challenges are
probing the evolution of molecular aggregates from a true solution and
directing the self-assembly process in a pre-defined fashion. The structure of molecular
aggregates in the solution can be predicted from fluorescence correlation spectroscopy (FCS) and dynamic light scattering
(DLS) analysis. On the other hand, the morphology of the aggregates can also be
visualized through electron microscopy. Nevertheless, a direct correlation
between emission from molecular aggregates in the aqueous dispersion and their
morphology obtained through a solid-state characterization is missing. In the present
study, we decipher the sequential evolution of molecular nanofibers from
solution to spherical and oblong-shaped nanoparticles through the variation of
solvent polarity, adjusting the <a>hydrophobic-hydrophilic
interactions</a>. The intriguing case of
molecular self-assembly is elucidated employing a newly designed π-conjugated
thiophene derivative (TPAn) through a combination of steady-state absorption, emission measurements, FCS, and electron microscopy. The FCS analysis and microscopy results infer that
small-sized nanofibers in the dispersion are further agglomerated, resulting in
a network of nanofibers upon solvent evaporation. <a>The
evolution of organic nanofibers and subtle control over the self-assembly
process demonstrated in the current investigation provides a general paradigm
to correlate the size, shape, and emission properties of diverse fluorescent
molecular aggregates in complex heterogeneous media, including a human cell. </a>
Deciphering Molecular Self-Assembly through Electron Microscopy and Fluorescence Correlation Spectroscopy