Gated photochromic reactivity of diarylethenes with visible-light-triggered turn-on fluorescence

All visible-light-driven fluorescent photo-switches are essential for high-density optical memories, whereas their gated photochromism remains a great challenge. Herein, we report the synthesis and photochromic properties of 2,3-bis(2-methyl-1-benzothiophene-1,1-dioxide-3-yl)-thiophene (BTTO4) based photochromic diarylethene isomers oDB, mDB, and pDB functionalized with N,N-dimethylaniline at three positions. These compounds all exhibit turn-on fluorescence upon visible light irradiation at 405 nm. Surprisingly, the cycloreversion reaction of para-substituted closed-isomer c-pDB was suppressed. Upon addition of trifluoroacetic acid, the acidic compound c-pDB•H+ was turned active, displaying an unusual gated photochromic property. Moreover, the photochromic reactivity can be suppressed again by neutralizing the acid with Et3N. To the best of our knowledge, this is the first report of gated photochromic diarylethene with visible-light-triggered turn-on fluorescence. This study provides a new type of all-visible-light triggered fluorescent photo-switches, and a novel "lock" and "unlock" system for photocycloreversion reactions.