Polarity-Induced Morphological Transformation with Tunable Optical Output of Terpyridine-Phenanthro[9,10- d ]imidazole-Based Ligand and Its Zn(II) Complexes with I - V Characteristics.

Self-assembled nanostructures obtained from various functional π-conjugated organic molecules have been able to draw substantial interest due to their inherent optical properties, which are imperative for developing optoelectronic devices, multiple-color-emitting devices with color-tunable displays, and optical sensors. These π-conjugated molecules have proven their potential employment in various organic electronic applications. Therefore, the stimuli-responsive fabrication of these π-conjugated systems into a well-ordered assembly is extremely crucial to tuning their inherent optical properties for improved performance in organic electronic applications. To this end, herein, we have designed and synthesized a functional π-conjugated molecule ( TP ) having phenanthro[9,10- d ]imidazole with terpyridine substitution at the 2 position and its corresponding metal complexes ( TPZn and (TP) 2 Zn ). By varying the polarity of the self-assembly medium, TP , TPZn , and (TP) 2 Zn are fabricated into well-ordered superstructures with morphological individualities. However, this medium polarity-induced self-assembly can tune the inherent optical properties of TP , TPZn , and (TP) 2 Zn and generate multiple fluorescence colors. Particularly, this property makes them useful for organic electronic applications, which require adjustable luminescence output. More importantly, in 10% aqueous-THF medium, TPZn exhibited H-type aggregation-induced white light emission and behaved as a single-component white light emitter. The experimentally obtained results of the solvent polarity-induced variation in optical properties as well as self-assembly patterns were further confirmed by theoretical investigation using density functional theory calculations. Furthermore, we investigated the I - V characteristics, both vertical and horizontal, using ITO and glass surfaces coated with TP , TPZn , and (TP) 2 Zn , respectively, and displayed maximum current density for the TPZn -coated surface with the order of measured current density TPZn > TP > (TP) 2 Zn . This observed order of current density measurements was also supported by a direct band gap calculation associated with the frontier molecular orbitals using the Tauc plot. Hence, solvent polarity-induced self-assembly behavior with adjustable luminescence output and superior I - V characteristics of TPZn make it an exceptional candidate for organic electronic applications and electronic device fabrication.