“…The molar extinction coefficients increase slightly, along with the change of the pull or push electron groups. Especially, we were surprised to discover that the introduction of the –SMe group led to low fluorescence quantum yield ( Φ f = 0.05), compared with other tBuazaBDP s. In sharp contrast to Rev-SMe-tBuazaBDP [ 52 ] with the group exchange at 1,7 and 3,5-sites ( Scheme 1 b) from SMe-tBuazaBDP , although the maxima emission between Rev-SMe-tBuazaBDP (λ em = 713 nm) and SMe-tBuazaBDP (λ em = 708 nm) could indeed be comparable, the maximum absorption of SMe-tBuazaBDP (λ abs = 602 nm) is obviously hypochromatic shift relative to that (λ abs = 666 nm) of Rev-SMe-tBuazaBDP , so SMe-tBuazaBDP shows a larger Stokes shift (106 nm) than that (47 nm) of Rev-SMe-tBuazaBDP . Therefore, a breakthrough of ultra-large Stokes shift was found in the spectral properties of 3,5-di- tert -butyl-substituted aza-BODIPYs in this work.…”