6-Aryl- and 6,7-diaryl-1,3-dimethyl-1<i>H</i>-perimidin-2(3<i>H</i>)-ones: synthesis, conformational stability, crystal structure and optical properties

6-Bromo- and 6,7-dibromo-1,3-dimethyl-1<i>H</i>-perimidin-2(3<i>H</i>)-ones were arylated with arylboronic acids under Suzuki-Miyaura reaction conditions to afford 6-aryl-, 6-bromo-7-aryl- and 6,7-diaryl-1,3-dimethyl-1<i>H</i>-perimidin-2(3<i>H</i>)-ones. A comparison of the X-ray structural parameters of <i>peri</i>-diaryl derivatives of 1,3-dimethyl-1<i>H</i>-perimidin-2(3<i>H</i>)-one, naphthalene and 1,8-bis(dimethylamino)naphthalene (proton sponge) was performed. Based on the data of dynamic ¹H NMR spectroscopy and quantum-chemical calculations, barriers to <i>syn</i>/<i>anti</i>-isomerization of 6,7-diaryl-1,3-dimethyl-1<i>H</i>-perimidin-2(3<i>H</i>)-ones were estimated. The optical properties of 6-aryl- and 6,7-diaryl-1,3-dimethyl-1<i>H</i>-perimidin-2(3<i>H</i>)-ones as structural analogs of fluorophoric 6-aryl- and 6,7-diaryl-1,8-naphthalimides were studied.