A naphthalene–phenanthro[9,10-d]imidazole-based π-conjugated molecule with a self-assembly-induced tuneable multiple fluorescence output exhibits artificial light-harvesting properties†

Abstract

Among promising new materials, π-conjugated organic molecules are considered an attractive platform for the design and development of a wide range of self-assembled superstructures with desirable optical and electrical properties necessary for use in organic optoelectronics applications. The optical and electrical properties of π-conjugated organic molecules and their possible applications are usually determined by their primary molecular structure and their intermolecular interactions in the self-assembled state. However, satisfying the structural requirements for achieving tuneable optical properties is a difficult task, which makes the design and development of novel high-performance π-conjugated organic systems for nano-optoelectronics a considerable challenge. In this paper, we report on the design and synthesis of a naphthalene–phenanthro[9,10-d] imidazole-based π-conjugated Schiff base molecule (L1) that exhibits aggregation-induced tunable luminescence properties facilitated by solvent polarity. Upon varying the medium polarity of the self-assembly medium, L1 self-assembles into various superstructures with distinct morphologies and generates multiple tunable emission colours (blue–green–yellow–white). In a highly polar THF : water = 1 : 9 medium, it displays aggregation-induced white light emission. These single component-based white-light emitters attract broad attention due to their potential applications in lighting devices and display media. Computational studies incorporating full geometry optimization, time-dependent density functional theory (TDDFT) calculations and molecular dynamics (MD) simulations were utilized to elucidate the enhanced π–π interaction influenced by increasing solvent polarity and orbitals involved in electronic transitions associated with different self-assembled states. More importantly, we constructed a highly efficient artificial light-harvesting system in a THF : water = 1 : 1 medium based on self-assembled L1 and rhodamine B (RhB), where L1 acts as an energy donor and RhB acts as an acceptor, exhibiting a strong antenna effect at a substantial donor/acceptor ratio. Our findings provide a novel versatile approach for developing efficient artificial light-harvesting systems based on the supramolecular self-assembly of suitably designed π-conjugated organic molecules with tuneable multiple emission properties.