Unravelling Delayed Luminescence Characteristics of Aminoboranes and Borylaniline: Fundamentals and Applications

Abstract

The advancement of organic delayed luminescence (thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP)) materials holds significant promise for applications in optoelectronics, bioimaging, and anticounterfeiting technologies. Despite the outburst of developments in this field of research, the structure-property correlations are not fully understood, which is essential for designing a molecule/material with desired properties. Thus, this thesis aims to address this gap by exploring systematic structural and optical studies on aminoboranes and substituted boryl anilines. The B-N moiety is isoelectronic and isostructural to C-C moieties; however, the electronegativity difference between B and N blesses B-N embedded systems with distinctive optical characteristics, such as through-bond CT. Furthermore, the inherent difference in their orbital and electronic configurations aids them in creating an excited state with the right symmetry (π-π* and n-π*), which offers high spin-orbit coupling (SOC) and enhances ISC and rISC, leading to an efficient delayed luminescence. The thesis begins with establishing the theoretical foundation of luminescence mechanisms and the significance of B-N systems.The research starts with investigating the influence of heteroatoms and conformational dynamics of aminoboranes on their DL properties. In subsequent chapters, carbazole-based systems are engineered to balance phosphorescence and delayed fluorescence by modulating substituents on the donor and acceptor units. These designs achieve dual emissions and temperature-dependent phosphorescence color switching, expanding their applications in anticounterfeiting. Building upon these findings, boron-containing multichromophore systems are designed and studied, demonstrating significantly enhanced photoluminescence quantum yields and biocompatibility compared to individual chromophores. Furthermore, these systems are employed for potential multicolor live-cell imaging. Following this, the exploration of regioisomeric borylanilines exhibits dual-mode delayed fluorescence and RTP emission, along with multi-stimuli-responsive optical properties. These materials were successfully utilized to develop rewritable inks for anticounterfeiting applications. Finally, polymorphic and geometrically diverse donor-acceptor systems based on naphthalimide are developed, emphasizing their structure-dependent biological responses and lysosome-specific imaging capabilities. This research establishes a comprehensive understanding of boron-nitrogen-based DL systems, showcasing their versatility in addressing technological challenges in optoelectronics, bioimaging, and anticounterfeiting. The outcomes of this work not only expand the fundamental knowledge of delayed luminescence materials but also provide a roadmap for designing next-generation luminescent systems with tailored properties for emerging applications.