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The photochromic properties of a chromene derivative, which contains a positively charged substituent, were investigated in the presence of ct DNA. Upon irradiation in the absence of DNA the colored quinoid open form is highly unstable and rapidly reverts back to the initial closed form (bleaching). In the presence of DNA the open form is significantly stabilized, presumably because of the association with the macromolecule. The kinetics of the bleaching reaction of the bound ligand were determined and employed to estimate the binding constant.

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The structures of six N-unsubstituted pyrazoles, three already known and three newly synthesized, have been studied by a combination of X-ray crystallography, multinuclear NMR (solution and solid state), and density functional theory (DFT) calculations. In those cases where crystal structure and CPMAS NMR were available, the agreement was almost perfect, allowing a prediction of the tautomer (with certitude) and the tetrameric structure (with high probability) in the case of 5-isopropyl-3-phenyl-1Hpyrazole without knowing the X-ray structure. In the case of the 5-(2-benzylphenyl)-3-trifluoromethyl-1H-pyrazole above represented, the DFT calculations at the B3LYP/6-31G** level justify the great stability of this tautomer by the presence of an intramolecular N-H‚‚‚π interaction, present in solution.