Approaches toward white light emission and programmable fluorescence, along with the serendipitous discovery of a series of pericyclic cascade reactions

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University of New Brunswick


Research in molecular fluorescence has led to more energy-efficient LED displays, single-molecule level detection limits in microscopy, and increasingly complex anti-counterfeiting measures. However, synthetic and design challenges associated with the realization of white, red, and blue light-emitting systems with the properties required for commercialization still exist. First, we explore the use of multicomponent photoluminescent systems, containing a mixture of simultaneously emitting organic molecules to access white light and programmable emission color. By mitigating the potential for energy transfer through the control of concentration, we show that the emission color is approximated as a linear combination of the emitting components and their corresponding brightness. Based on these results, we demonstrate that the ratio of red, green, and blue emitters needed to achieve hard-to-reach WLE can be predictably determined. Second, we show that one molecular scaffold, thioarylmaleimide (TAM), can be used to access blue to deep-red emission colors with high quantum yields in just one synthetic step. A series of mono and bis-substituted TAMs are synthesized from commercially available starting material in moderate to excellent yields via Suzuki-Miyaura (SM) cross-coupling. Photophysical properties, including wavelength and quantum yield, are controlled by adjusting the conjugation, connectivity, and the number of thioaryl groups attached to the maleimide. A marked decrease in the SM coupling yield of monosubstituted TAMs prompted the serendipitous discovery of a series of pericyclic cascade reactions leading to crowded thienyl and benzo[b]thienyl fused architectures. Stereochemical assignment is achieved using a combination of NMR studies, chemical shift calculations and DP4+ analysis. Transition-state calculations support an asynchronous concerted mechanism and provide support to rationalize the regio- and diastereoselectivity that is observed.