White light employing luminescent engineered large (mega) Stokes shift molecules: a review

Large (mega) Stokes shift molecules have shown great potential in white light emission for optoelectronic applications, such as flat panel display technology, light-emitting diodes, photosensitizers, molecular probes, cellular and bioimaging, and other applications. This review aims to summarize recent developments of white light generation that incorporate a large Stokes shift component, key approaches to designing large Stokes shift molecules, perspectives on future opportunities, and remaining challenges confronting this emerging research field. After a brief introduction of feasible pathways in generating white light, exemplifications of large Stokes shift molecules as white light candidates from organic and inorganic-based materials are illustrated. Various possible ways to design such molecules have been revealed by integrating the photophysical mechanisms that are essential to produce red-shifted emission upon photoexcitation, such as excited state intramolecular proton transfer (ESIPT), intramolecular charge transfer (ICT), excited state geometrical relaxation or structural deformation, aggregation-induced emission (AIE) alongside the different formations of aggregates, interplay between monomer and excimer emission, host-guest interaction, and lastly metal to ligand charge transfer (MLCT) via harvesting triplet state. Furthermore, previously reported fluorescent materials are described and categorized based on luminescence behaviors on account of the Stokes shifts value. This review will serve as a rationalized introduction and reference for researchers who are interested in exploring large or mega Stokes shift molecules, and will motivate new strategies along with instigation of persistent efforts in this prominent subject area with great avenues. Illustration of white light designated with the 1931-CIE coordinate of (0.33, 0.33), and photophysical mechanisms that contribute to large Stoke shift molecules.