Global CO2 emissions arising from electrical lighting are competitive with those arising from transportation, thus the development of next generation lighting technologies promises to mitigate greenhouse gas production. Triazolopyridinium (TOP) and BF2-hydrazone (BODIHY) hydrazone-based dyes have promising fluorescent properties for next generation lighting applications. Specifically, TOP dyes have large Stokes shifts and broad emission bandwidths, while BODIHY dyes have highly efficient solid state emission. However, ambiguity regarding the fundamental origins of these photophysical properties has slowed the development of new TOP and BODIHY dyes with fluorescent properties optimized for next generation lighting technologies. Density functional theory (DFT) computations, coupled with spectroscopic experiments, have been employed to provide accurate molecular orbital-based models of hydrazone-based dye absorption, excited state relaxation, and fluorescence. Recently, time-dependent DFT (TDDFT) modelling of TOP dyes revealed why the Stokes shift significantly decreases upon dimerization; the excitation transition changes from an aryl to heterocycle charge transfer to a π→π* transition within the heterocyclic group. TDDFT optimization of the photoactive excited state accurately predicts a large Stokes shift on the order of 10,000 cm-1 and provides a detailed picture of the excited state distortion. DFT and TDDFT computations have also been applied to a series of BODIHY dyes to provide detailed explanations for unexpected trends in their condensed phase brightness. Ultimately, these DFT computations aid the rational design of novel TOP-based fluorophores with carefully tuned Stokes shifts and emission bandwidths, as well as critical insight into the quantum mechanical origins of solid-state fluorescence for BODIHY-based fluorophores.

Insight Into hydrazone-based dye fluorescence from density functional theory

249th National Meeting (2015)

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