Halochromic Molecules. Synthesis and Acidobasic Properties of Substituted HeteroarenoquinazolinesWe have synthetized a series of substituted heteroarenoquinazolines. The 90‐MHz FT1H‐NMR spectra of starting and final products supported the postulated structures. Fragmentation in the mass spectra also were consistant with the assumed structures. With acid, the compounds partly from ring‐opened, intensely coloured triphenylcarbenium salts of the Rhoduline‐R type (C. I. 42565). UV/VIS spectra of the salts are discussed on the basis of VEPPP‐CI calculations. The ϵpH*curves in buffered MeOH/H2O solutions and the pK* values are determined. The title compounds undergo very complex protonation