Azaisoquinolinones: N Positions Tell You Different Stories in Their Optical Properties

Since
isoquinolinones and their derivatives have been demonstrated
to be powerful building blocks in constructing larger acenes and twistacenes,
azaisoquinolinones and their analogues could also be important intermediates
to approach larger N-heteroacenes. In this paper, we are interested
in developing a concise method to synthesize novel azaisoquinolinones
building blocks and studying their physical properties. Our results
showed that the different N positions have a large effect on the optical
and electrochemical properties of azaisoquinolinones. For example,
protonation of 6- and 7-azaisoquinolinones shows different shifts
of UV–vis and FL spectra. More interestingly, 6- and 7-azaisoquinolinones
exhibited different interactions with metal ions in CH3CN solution. Upon the addition of 2 equiv of Fe3+, 6-azaisoquinolinone
displayed an absorption wavelength red-shifted from 470 to 540 nm
(Δλ = 70 nm) with a color change from yellow to red, while
the interaction between Fe3+ and 7-azaisoquinolinone was
very weak and there was no obvious color change (Δλ =
18 nm). Moreover, theoretical calculations confirmed the different
optical properties with 6- and 7-azaisoquinolinones.