Probing the Aggregated State of 4-(9-Anthryl)-N,N-dimethylaniline by UV-Vis Absorption and Fluorescence Spectroscopy, Microscopy, and Crystallography

The aggregated state of the electron donor-acceptor molecule, 4-(9-anthryl)-N,N-dimethylaniline, abbreviated here as ADMA, has been studied by electronic absorption and fluorescence spectroscopy, microscopy, and crystallography. Self-assembled aggregates have been prepared by reprecipitation method under various conditions without using any stabilizing agent and characterized by different microscopic techniques. These studies reveal spherical and platelike morphologies and both amorphous and crystalline nature of the aggregates, whose sizes vary between 250 and 600 nm. The optical properties of these well-characterized aggregates have been studied and compared with those in molecular form. Intermolecular interaction in the aggregates induces remarkable change in the absorption and fluorescence properties of this dipolar system, and the formation of stable aggregates can be conveniently followed by monitoring the spectra] response of the system as a function of time. Intramolecular charge transfer process, which dominates the photophysical behavior of this molecular system, could not be observed in the solid or aggregated state. The nature of the intermolecular interactions responsible for the formation and stabilization of the aggregates has been identified from the spectral and crystal structure data of the system. The results highlight the scope of broadening the spectral response of the present system by exploiting the advantageous optical properties of the aggregated state of the molecule.