Near-infrared II photochromic behavior triggered by green light in an in situ protonated dithienylethene functionalized by quinoxalinone moieties

Abstract

Exploiting the near-infrared (NIR) photochromic dithienylethenes (DTEs) triggered by visible light is urgently needed for a wide variety of biological scenarios. However, all the reported NIR photochromic DTEs so far are located in the first NIR window (NIR-I, 700-900 nm), which usually shows shallower penetration in biological tissues due to autofluorescence and photon scattering compared to NIR light in the second window (NIR-II, 1000-1700 nm). Herein, we present a novel quinoxalinone-functionalized DTE derivative (QDTE) with acceptor (A)-DTE-acceptor (A) structural features, in which electron-withdrawing quinoxalinone groups ensures visible light-driven NIR I photochromism. Besides, the facile protonation of the quinoxalinone moieties favors the formation of the more electron-deficient A-A-type DTE (QDTE-2H) for a unique NIR II photochromism by reducing HOMO-LUMO energy gap of closed isomer after protonation. As expected, the resulting QDTE displays a blue light-controlled NIR I photochromic performance in various solvents. Furthermore, an unprecedented green light-triggered NIR II photochromism for the in situ protonated QDTE-2H is successfully implemented in CHCl3 and toluene in the presence of trifluoroacetic acid (TFA), representing the first case of NIR II photochromic DTE. By virtue of these, QDTE has been successfully applied in dual information encryption, demonstrating its versatility in functional materials.