From ACQ to AIE: The CN(π)-(π)Ar interaction driven structural and photophysical properties of aromatic ring conjugated novel diaminomaleonitrile derivatives

Abstract

Studying solid and solution state photoluminescence properties are exclusive to understanding Aggregation Caused Quenching (ACQ) and Aggregation Induced Emission (AIE) behaviour of organic molecules to explore the mechanism of molecular luminescence in greater detail. A unique hydrogen-bonded dimer with imperative interaction (CN)π---π(Ar) was designed and synthesized by selecting diaminomaleonitrile (DMN) as stator and decorated with different aromatic rotors (phenyl to pyrene). Depending on the intermolecular interaction present in the molecular system, (AIE) or (ACQ) has been observed and found to be tunable. The single-crystal x-ray diffraction analysis of these derivatives shows that AIE characteristics could be seen where to (CN)π---π(Ar) intermolecular interactions between the aromatic rotors and stator, coupled with NH–-–NC intermolecular hydrogen bonding is present, while the absence of these interaction reflected in ACQ observation. The significant impacts of steric, conjugation and electronic effects on the ACQ / AIE properties are presented based on crystallography analysis, optical spectra measurements and theoretical calculations.