We study the effect of molecular conformation on the electronic coupling between the donor amines and acceptor 1,8-naphthalimide (NPI) in a series of D–A systems 1–4 (A = NPI; D = phenothiazine, phenoxazine, carbazole, diphenylamine, respectively, for 1, 2, 3, and 4). Weakly coupled systems show dual emission in the solution state, while strongly coupled systems show single emission bands. The energy of transitions and photoluminescence (PL) quantum yield are sensitive to the molecular conformation and donor strength. These compounds show delayed emission in the solutions and aggregated state and phosphorescence in the solid state. Compounds 3 and 4 with weak donors exhibit intermolecular slipped π···π interactions in the solid state and consequently exhibit dual (intra- and inter-) phosphorescence at low temperature. Steady state and time-resolved PL studies at variable temperature together with computational and crystal structure analysis were used to rationalize the optical properties of these compounds. The delayed emission of these compounds is sensitive to molecular oxygen; accordingly, these molecules are utilized for differential imaging of normoxia and hypoxia cancer cells.

An efficient green synthetic approach has been developed towards the synthesis of 2-aryl substituted benzimidazoles 4 from α-aroylketene dithioacetals (AKDTAs) 1 and phenylenediamine (OPD) 2.

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An efficient chemo/regio/stereoselective synthesis of novel and functionalized spiro-oxindole/pyrrolizine/ pyrrolidine scaffolds has been achieved. The in situ generated azomethine ylide from isatin & L-proline/ phenyl alanine underwent 1,3-dipolar cycloaddition with a-aroylidineketene dithioacetals under simple reaction conditions affording spiro-oxindole derivatives. This protocol exhibits an interesting double bond selectivity of a-aroylidineketene dithioacetals. Furthermore, utilizing this spiro-oxindoles scaffold, biologically important benzimidazole and pyrimidine based poly heterocycles were also synthesized.