Synthesis and Photochromic Properties of Bis-Spirocyclic Compounds Based on 1,3-Dihydroxy-6-oxo-6H-benzo[c]chromene-2,4-dicarbaldehyde

Nonsymmetric bis-spiropyran derivatives based on 1,3-dihydroxy-6-oxo-6H-benzo[c]chromene-2,4-dicarbaldehyde were synthesized. The obtained compounds with substituents R = H, Cl at positions 5,5′ of the indoline fragment in DMSO solution exist in a fully open merocyanine form. Their change for the electron-acceptor group NO2 results to the existence of the corresponding bis-spiropyran in the form of a tautomeric mixture of spirocyclic and merocyanine forms. The resulting compounds in DMSO solution undergo photoinduced cyclization. The nitro derivative demonstrates both positive and negative photochromism.