Ferrocene‐Grafted Photochromic Triads Based on a Sterically Hindered Ethene Bridge: Redox‐Switchable Fluorescence and Gated Photochromism

Abstract

Multifunctional switches, as well as gated photochromism, are particularly challenging. Here, a ferrocene (Fc)‐modified photochromic diarylethene (DAE) with sterically hindered ethene bridge, in which the photo‐inactive parallel conformer and photoactive antiparallel conformer are individually investigated, is reported. The photoswitchable triad system (parallel conformer p‐Fc and anti‐parallel ap‐Fc) contains three functional parts: photochromic DAE unit, naphthalimide chromophore, and redox‐active ferrocene. Upon incorporation of ferrocene unit, the photochromic efficiency in the anti‐parallel triad conformer ap‐Fc is blocked to a great extent in the ferrocene state but distinctly enhanced in the ferrocenium state via chemical or electrochemical stimuli, thereby constructing redox‐gated photochromism. Meanwhile, the reversible redox between ferrocene and ferrocenium states can also switch “OFF/ON” the fluorescence of naphthalimide chromophore via photoinduced electron transfer pathway (PET). The fluorescence and photoisomerization in the triad system are well modulated with chemical‐ or electrochemical redox and light stimuli, which enables the specific gated photochromism and fluorescence switches work in multi‐addressable states.

Research advances in the synthesis and applications of ferrocene‐based electro and photo responsive materials

“…Upon increasing the proportion of the oxidizing agent, the signals of methylene moiety were shifted downfield and finally, they totally vanished indicating the complete oxidation. The disappeared resonances gradually recovered upon addition of reducing agent showing the reversible redox behavior . The use of diarylethene is limited due to the problem of oxidation which renders the entire sequence irreversible.…”

“…Cai et al . synthesized some photoinduced electron transfer (PET) generators having diarylethene (DAE) as a photoswitchable unit and ferrocene‐based naphthalimide . It was found that ferrocene grafted triads can give electro and photoresponsive properties by changing the source of light or redox cycle (Figure ) .…”

“…synthesized some photoinduced electron transfer (PET) generators having diarylethene (DAE) as a photoswitchable unit and ferrocene‐based naphthalimide . It was found that ferrocene grafted triads can give electro and photoresponsive properties by changing the source of light or redox cycle (Figure ) . Upon incorporation of ferrocene unit (Fc), the photochromic efficiency in the anti‐parallel triad conformer ap‐Fc was blocked to a great extent in the ferrocene state but distinctly enhanced in the ferrocenium state via chemical or electrochemical stimuli, thereby constructing redox‐gated photochromism.…”

“…Abs: THF solution in daylight and FL: Fluorescence of THF solution excited at isobestic point of 360 nm. Adopted with permission from ref. Copyright 2016, Wiley Online Library…”

“…Cai and co‐workers further explained the mechanism of this ferrocene‐based triad system . They suggested that the fluorescence quenching of naphthalimide in the ferrocene‐grafted triad system might be attributed to the PET pathway from the ferrocene unit to naphthalimide chromophore.…”