Molecular Engineering Approaches Towards All-Organic White Light Emitting Materials.

White light emitting (WLE) materials are of increasing interest owing to their promising applications in artificial lighting, display devices, molecular sensors, and switches. In this context, organic WLE materials cater to the interest of the scientific community owing to their promising features like color purity, long-term stability, solution processability, cost-effectiveness, and low toxicity. The typical method for the generation of white light is to combine three primary (red, green, and blue) or the two complementary (e.g., yellow and blue or red and cyan) emissive units covering the whole visible spectral window (400-800 nm). The judicious choice of molecular building blocks and connecting them through either strong covalent bonds or assembling through weak noncovalent interactions are the key to achieve enhanced emission spanning the entire visible region. In the present review article, molecular engineering approaches for the development of all-organic WLE materials are analyzed in view of different photophysical processes like fluorescence resonance energy transfer (FRET), excited-state intramolecular proton transfer (ESIPT), charge transfer (CT), monomer-excimer emission, triplet-state harvesting, etc. The key aspect of tuning the molecular fluorescence under the influence of pH, heat, and host-guest interactions is also discussed. The white light emission obtained from small organic molecules to supramolecular assemblies is presented, including polymers, micelles, and also employing covalent organic frameworks. The state-of-the-art knowledge in the field of organic WLE materials, challenges, and future scope are delineated.