Synthesis and Photophysical Properties of 4,4′‐ and 5,5′‐Substituted Bis(phenolate) Aza‐GaDIPYs

An investigation into the photophysical effects of a series of 10 bis(phenolate) aza‐GaDIPYs with regioselective substitution on the 4,4′‐ and 5,5′‐positions of the phenolate rings was conducted. Computational and experimental data confirmed that installation of strong π‐electron donors on the 5,5′‐positions provided maximized bathochromic shifts in both absorption and emission spectra as well as larger Stokes shifts when compared to the 4,4′‐isomers. This can be rationalized by how the 5,5′‐positions interact strongly with the HOMO and weakly with the LUMO, thus narrowing the HOMO‐LUMO gap. Combined, these data demonstrate that judicious functionalization of the phenolate rings represents a reliable strategy to achieve absorption and emission maxima above 800 nm.