B, N containing π- conjugated systems: room temperature phosphorescence, fullerene complexation, and cell differentiation

Abstract

Advances in heteroatom (B, N, and B-N) incorporated π-conjugated systems have attracted considerable attention because of their desirable properties and widespread applications. Substitution of isoelectronic B–N units for C=C units in π-conjugated systems produce novel materials with structural similarities to all-carbon frameworks but with fundamentally altered electronic and optical properties. However, despite significant progress in this field, there is a lack of systematic studies of their fundamental properties like solid/condensed state optical behaviour of BN compounds. The objective of this thesis is to synthesize boron-nitrogen-containing compounds and to investigate their photophysical properties and applications. As part of this program, we have demonstrated the host-guest chemistry of B-N doped polyaromatic heterocycles (BN-PAHCs) for the first time. Further, we developed doubly B-N fused Ni(II) porphyrins with ruffled core structures and studied their opto-electrochemical behaviours. We have also explored the potential of aminoboranes as a new class of persistent room-temperature phosphorescent materials by modulating their electronic properties upon judiciously varying the substituents in the B-N unit. Novel anthracene-boron-based luminophores were synthesized. These compounds exhibit intriguing optical properties such as aggregation-induced emission enhancement (AIEE) and microviscosity-dependent emission. The unique optical features of these compounds have been successfully exploited for differentiating normal, autophagic, and apoptotic cells. Encouraged by these promising results, a series of molecules consisting of both tri and tetracoordinate boron centers were synthesized. The non-planar geometry of tetracoordinate boron combined with sterically demanding tricoordinate dimesitylboron unit inhibits π-stacking interactions and leads to strong luminescence in the solid state. Furthermore, we accidentally discovered a rare class of tribophosphorescent materials with molecular architecture composed of triboluminescent moiety (anthracene) and an ISC facilitator (-Bpin). This serendipitous discovery unveiled a new design strategy for developing tribophosphorescent molecules. This thesis contains all of these fascinating findings.