Synthesis, photochromism and photomagnetism of new biindenylidenedione derivatives in crystalline state

A new class of biindenylidenedione compounds, namely 3,3′-dialkyl-3,3′-dihydroxy-6,6′,7,7′-tetramethoxy-[2,2′-bi-1H-indene]-1,1′-dione 3a–3d (alkyl = ethyl, n-propyl, n-butyl and n-pentyl), have been synthesized and characterized by IR, 1H NMR, 13C NMR, MS, HRMS, elemental analysis and the single X-ray crystallography. The photochromic and photomagnetic properties were studied by means of solid UV–vis spectroscopy, electron spin resonance (ESR) and superconducting quantum interference device (SQUID) susceptometer, respectively. The results showed that all these compounds simultaneously exhibited photochromism and photomagnetism in crystalline state. The structure–property relationships are discussed in context of the intra- and inter-molecular interactions.