SOLID-STATE EMISSION

Conventional knowledge and understanding of luminescent dyes have been restricted to solution-state realms for a rather long time. [1] However, practical applications of any given material greatly rely on its compatibility in solid-state. In most instances, commonly encountered luminescent dyes show very poor or no emissive features in their condensed or solid-state, resulting from the effects of strong intermolecular forces, which lead to self-quenching of luminescence. Thus, considerable scientific interests are being drawn towards the developments of solid-state emissive organic emitters owing to their potential applications in OLEDs, security, Lighting, and sensing. A solid-state emitter's design might not be straightforward, and often successes are met only through hit-and-trail methods or brute-force synthetic strategies. However, if one wants to gain insights into solid-state emitters' structure-property relationships, systematic design strategies can be of significant interest. In recent years, our research group has been involved in imparting solid-state emissive properties in boron-based dyes and NPIs. [2-4] These classes of compounds were well-known for their versatile photophysical properties in solution-state, photo-stability, and tunable emission features. However, these dyes suffer from significant quenching of luminescence in their solid-state due to considerable p-p stacking interactions and related strong intermolecular forces. In our efforts, we were able to systematically fine-tune the substitution pattern in these classes of compounds, resulting in an alteration of their molecular flexibility and the nature of intermolecular interactions. Furthermore, the systematic alterations of the compounds' molecular structures also provided significant insights into the controlling parameters that affect the bulk emissive features of such compounds. The correlation between the color, quantum yields, and structural patterns of the compounds reflects that small changes at the molecular level can significantly alter bulk-state emissive properties. Also, it is unveiled that p-p interactions can be either detrimental or beneficial depending on the relative arrangements of neighboring luminescent units. This understanding of luminescent materials is of significant and fundamental interest to gain a broader understanding of structure-property relationships in luminescent materials.