Design and Synthesis of a New Class of Photochromic Diarylethene-Containing Dithieno[3,2-b:2′,3′-d]pyrroles and Their Switchable Luminescence Properties

A series of dithienylethene-containing dithieno[3,2-b:2',3'-d]pyrroles were synthesized and their photophysical study was done. Tetrabromination of dithieno[3,2-b:2',3'-d]pyrrole followed by subsequent Suzuki cross-coupling reaction in the presence of an excess of 2,5-dimethylthien-3-yl boronic acid, aqueous Na2CO3 and a catalytic amount of [Pd(PPh 3)4] was used in THF under reflux conditions. Compounds 1-5 were characterized by 1H NMR spectroscopy, EI-MS, and give satisfactory elemental analyses, while the structures of compound 2 and 3 were determined by X-ray crystallography. Compounds 1-5 dissolve in benzene and they showed similar UV/Vis absorption spectra with an intense band at about 350 nm. Upon excitation at the transition band at 360 nm in degassed benzene, the solutions of compound 1-5 showed photochromic behavior, turning from colorless to reddish purple, with the growth of an intense absorption band at approximately 290 and 352 nm were observed.