Diarylethene-based conjugated polymer networks for ultrafast photochromic films

Diarylethene polymers are an emerging class of photochromic materials which offer new opportunities for the development of optical data recording and storage. This work reports two diarylethene-based conjugated polymer networks DPP-1 and DPP-2 constructed by Schiff-base polymerization of two-connected photochromic unit 1,2-bis(5-formyl-2-methylthiophen-3-yl)perfluorocyclopentene (DEA-CHO) and tetrahedral four-connected unit tetra(p-aminophenyl)methane (TAPM) or plane three-connected unit 1,3,5-tris(4-aminophenyl)triazine (TAPT). The molecular structures of DPP-1 and DPP-2 were characterized by FT-IR and C-13 CP-MAS solid state NMR spectroscopy, and the morphology was investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The model compound was used to indicate the possibility of constructing DPP-1 and DPP-2. DPP-1 and DPP-2 exhibited high chemical stability in the presence of strong acid (6 M HCl) and strong base (6 M NaOH) for 5 days. DPP-1 and DPP-2 showed ultrafast photochromic transformation between the open form (yellow) and closed form (green) with alternate irradiation of ultraviolet and visible light in 50 seconds, which were measured through UV-vis-NIR experiments. X-ray photoelectron spectroscopy (XPS) demonstrated that the electronic arrangement around the sulfur atoms changed during the process of the open form to the closed form. Moreover, DPP-1 and DPP-2 displayed excellent fatigue resistance that the absorbance only lost ca. 5% after three cycles. DPP-1/PMMA and DPP-2/PMMA films fabricated by dispersing diarylethene-based conjugated polymer networks in the poly(methyl methacrylate) (PMMA) matrix also exhibited great photochromic reversibility and fatigue resistance, which provide potential applications towards the development of optical rewritable patterning and information storage devices.