It is very challenging to construct photochromic materials with absorption and reactivity in the near-infrared (NIR) spectral region. Herein, four unsymmetrical diarylethene derivatives 1o–4o, which contain both indole and thiophene moieties, have been successfully synthesized, and their photochromic behaviors have been shifted to the NIR region. These newly developed NIR photochromic materials are highly sensitive and responsive to photostimuli both in solution and in poly(methyl methacrylate) films. It has been shown that 1o–4o exhibit remarkable UV/Vis and fluorescence spectral changes, allowing them to behave as reversible optical molecular switches in the NIR region.

Stable nitronyl nitroxide radical and imino nitroxide radical were incorporated into the benzene rings of novel photochromic 7,7′-dimethyl-[2,2′-bi-1H-indene]-3,3′-diethyl-3,3′-dihydroxy-1,1′-dione (1), leading to the synthesis of novel multifunctional compounds 4 and 5. The photochromic properties, ESR spectroscopy and magnetic properties of the title compounds were investigated. Compounds 4 and 5 possess visible photochromism upon photoirradiation, and their ESR signals undergo secular broadening after photoirradiation. The magnetic susceptibility measurement shows that the antiferromagnetic interaction of 4 and 5 becomes stronger after photoirradiation. In compounds 4 and 5 there are two kinds of spin centers after photoirradiation: one is nitroxide radical, and the other is photo-generated radicals from two indanone moieties. Our results demonstrated that the colour and magnetic properties of compounds 4 and 5 could be modulated by photoirradiation.

A series of naphthopyrans with hydrazone unit (8a–8m), were synthesized and characterized by ¹H NMR, ¹³C NMR, IR and HRMS. The photochromic properties were investigated under continuous irradiation, in particular regard to the fatigue resistance and the lifetime of the colored open form in solution and polymers. The results showed that these compounds had both good photochromic properties and high fatigue resistance. Detailed studies showed that representative compound 8d (3,3-di-4-methoxybenzoic acid methylenehydrazino-[3H]-naphtho [2,1-b]pyran) had good photochromic properties in THF solution, in solid state, and in polymers, and exhibited a significant bathochromic shift in the spectra of the open forms compared to known naphthopyrans 9 (3,3-diphenyl-[3H]-naphtho[2,1-b]pyran). On the other hand, the higher melting points of target compounds are promising for the polymer film preparation through hot-melt method.

Photochromic 6-bromomethyl-6′-methyl-[2,2′-bi-1H-indene]-3,3′-diethyl-3,3′-dihydroxy-1,1′-dione (2), 6,6′- bis(bromomethyl)-[2,2′-bi-1H-indene]-3,3′-diethyl-3,3′-dihydroxy-1,1′-dione (3) and 6,6′-bis(dibromomethyl)-[2,2′- bi-1H-indene]-3,3′-diethyl-3,3′-dihydroxy-1,1′-dione (4) have been synthesized from 6,6′-dimethyl-[2,2′-bi-1H- indene]-3,3′-diethyl-3,3′-dihydroxy-1,1′-dione (1). The single crystal of 4 was obtained and its crystal structure was analyzed. The results indicate that in crystal 4, molecular arrangement is defective tightness compared with its precursor 1. Besides, UV-Vis absorption spectra in CH₂Cl₂ solution, photochromic and photomagnetic properties in solid state of 2, 3 and 4 were also investigated. The results demonstrate that when the hydrogen atoms in the methyl group on the benzene rings of biindenylidenedione were substituted by bromines, its properties could be affected considerably.