Solid state photochromism of pyrano[3,2-c]chromen-5-one moiety with the assistance of localized surface plasmons

Abstract

In this article, a photochromic dye, 3-bromo-2,2-dimethyl-2H-pyrano[3,2-c]chromen-5-one in its closed form (DDPC-CF), was coated with four different shapes of silver nanoparticles: nanospheres (AgS), nanoprisms (AgP), nanowires (AgW), and nanodisks (AgD), respectively. The resulting films, AgS-DDPC-CF, AgP-DDPC-CF, AgW-DDPC-CF, and AgD-DDPC-CF, have been fabricated on glass. Upon irradiation with UV light at various irradiation wavelengths, AgS-DDPC-CF, AgP-DDPC-CF, AgW-DDPC-CF, and AgD-DDPC-CF underwent a ring opening reaction to produce the opened forms AgS-DDPC-OF, AgP-DDPC-OF, AgW-DDPC-OF and AgD-DDPC-OF, respectively. It is found that the excitation of localized surface plasmons between the silver nanoparticles–silver nanoparticles could enhance the photochromic reaction efficiency in comparison with that of DDPC alone. The enhancement factor (E) and the volume percentages of the enhanced areas (F_E) in the entire shell of the forward photochromic reaction of AgS-DDPC to AgD-DDPC depending on the irradiation wavelength can be deduced to be 1–12 (30–65%), 1–2 (30–55%), 1–23 (50–70%), and 2–30 (55–70%), respectively. The E factor (and F_E) of the recovery photochromic reaction of AgP-DDPC and AgD-DDPC on glass can be deduced to be 20 (68%) and 3 (51%). The results show promising photochromic reaction efficiency values (e.g.AgP-DDPC and AgD-DDPC) that are enhanced greatly by the silver nanoparticles. Furthermore, the kinetics of AgS-DDPC to AgD-DDPC upon irradiation demonstrated here implies an acceleration of the photochromic reaction due to excitation of localized surface plasmons. AgP-DDPC and AgD-DDPC have a good photochromic reversibility during the photoinduced forward and reverse processes. Such a switching process of AgP-DDPC and AgD-DDPC can proceed for at least 10 cycles. The results should exemplify a model to investigate the photophysical properties of relevant chromenes in the solid state, especially their photochromic properties with improved conversion performance and the associated applications.