Synthesis and Characterization of a Few Organic Small Molecules as OLED Materials for Device Applications

Abstract

Efficient molecular design and synthesis of novel fluorescent organic small molecules have attracted significant attention among the researchers for their promising solid-state lighting applications. Precise bandgap engineering of an organic molecule achieved by various chemical routes have shown significant progress in the past few decades by generation of different color emission, sweeping over the entire visible spectrum. Ease of functionalization, a good stability under wider range of operating conditions and a low-cost synthetic route have always motivated researchers in developing novel molecules for optoelectronic applications. The present work is aimed at design and synthesis of few organic small molecules to uncover some of its interesting photophysical phenomena. Solvatochromic behavior of all the molecules of the series were studied under solvents of varying dielectric constants. Precise bandgap tuning achieved by variation of ancillary substituents on the core system was successful in generation of vivid emission colors. Solid-state emission of few of the molecules of the series exhibited an emission intensity higher in comparison with their solution state supporting aggregation induced emission (AIE) phenomena. Single crystal X-ray analysis on few of the molecules resulted in system adopting a larger intermolecular π-π stacking that would in turn block all the non-radiative channels leading to enhanced emission upon aggregation. Design strategies of few of the synthesized molecules resulting in an optimal HOMO and LUMO energy levels were successfully realized for OLED device applications. Density functional calculations on series were carried out to understand the nature of geometry at its ground state along with their electronic orbital information. Estimated electronic transitions for few of the series correlate well with the experimental absorption and emission energy transitions. Theoretical calculations uncovering excited state proton transfer dynamics resulting in estimation of excited state proton transfer barrier, questionable step-wise or hypothetical simultaneous double proton transfer for few of the molecular series were well discussed.