Spectral shifts of BODIPY derivatives: a simple continuous model

The BODIPY dyes are a versatile family of chromophores that have found use in fluorescence based bioimaging and other applications. The BODIPY core can be substituted in a vast number of ways, but the photophysical changes, such as shifts in absorption spectra, are not always immediately obvious from the molecular structure. We introduce a simple model that let you vary the electron withdrawing or electron donating character of each substituent continuously to get an overview of the landscape of possible spectral shifts. The features of substituted BODIPY cores are compared to the corresponding linear system, giving a new perspective on BODIPY photophysics. Using the model, we are able to rationalize the trend seen in a family of BODIPY, with chalcogen-containing substituents, as being due to a change in electronegativity.