Pyrazolo-fused 4-azafluorenones as key reagents for the synthesis of fluorescent dicyanovinylidene-substituted derivatives.

A green process to access pyrazolo-fused 4-azafluorenones (indeno[1,2-]pyrazolo[4,3-]pyridines, IPP) 4a-x the three-component reaction between indan-1,3-dione (1), benzaldehydes 2 and 5-amino-1-arylpyrazoles 3 is described. These compounds were successfully used as precursors of the novel dicyanovinylidene derivatives 7a-d containing different acceptor (A) or donor (D) aryl groups at position 4 of its fused system. The structures of products obtained (4a-x and 7a-d) were determined based on NMR experiments, HRMS analysis, and X-ray diffraction studies for 7b. The photophysical and computational studies of 7a-d showed that these products are modulable ICT fluorophores, even some preliminary tests revealed that these compounds could be used as fluorescent chemodosimeters for cyanide detection.