Electrofluorochromism: from molecular systems to set-up and display

Abstract

Electrofluorochromism deals with electrochemical monitoring of luminescence features. There are several reasons to be interested in that field. The first one is the design of displays working in a similar way to electrochromic devices, substituting colors due to absorption with colors due to emission, thus producing much higher brilliance. This requires designing smart molecules and materials, which are likely to exhibit reversible switch of emission by controlling their redox state. There are also a lot of analytical applications, especially in biochemical issues, where in situ dual detection of electrochemical and fluorescence signals can lead to very sensitive and selective biosensors. To achieve this goal, instrumental developments are necessary, involving, among others, beyond diffraction limit and single molecule detection optical techniques. This paper reviews the most recent developments in the above mentioned fields of fluorescence spectroelectrochemistry, coupled detection of fluorescence and electrochemical signals and design of molecules and materials exhibiting electrofluorochromic properties. The first part describes the required features for molecular systems to exhibit a reversible switch in their luminescence properties according to a change in their redox state. Examples among organic and organometallic dyes and redox labelled fluorophores are listed. The second part focuses on the instrumental development in fluorescence spectroelectrochemistry and recent coupling of electrochemical techniques with fluorescence microscopy.Finally, some applications and devices are presented in the last part of this review. This should give an overview of this emerging research field at the interface between physics, chemistry and biology.

Electrofluorochromism in π-conjugated ionic liquid crystals

“…The more straightforward way to electrofluorochromism is the direct electrochemical fluorescence switching through the formation of ion and neutral radicals. However, while the latter are not fluorescent or exhibit very low fluorescence, the first ones are usually not stable and their electrochemically monitoring is challenging 8 . Such main limitations have hampered the development of this class of molecules.…”

“…Specifically, materials in which photoluminescence is modulated by redox processes are known as electrofluorochromic 7 . They can be broadly classified into switchable molecular dyads and intrinsically switchable electroactive fluorophores 8 . In the first case, the fluorophore is linked to a redox moiety that acts as fluorescence switching through energy 9,10 or electron transfer mechanisms [11][12][13][14] .…”

Electroswitchable optical device enabling both luminescence and coloration control consisted of fluoran dye and 1,4-benzoquinone

“…Among these multifunctional materials, electrical stimuliresponsive molecules are particularly suitable for display applications because the electrical stimuli can be applied rapidly and reversibly [39][40][41][42][43][44][45]. Because of these advantages, electrical stimuli have attracted much attention.…”

Electrochemical switching fluorescence emission in rhodamine derivatives

“…Especially electrofluorochromism, in which fluorescence of molecules can be modulated electrochemically, is becoming a very attractive approach in analytical and bioanalytical chemistry since many analytes are redox active and can be detected and/or mapped with high sensitivity through fluorescence [1,2]. Even though electrochemical fluorescence modulation is becoming a promising approach, only a few systems based on single fluorescent molecules [3e7], molecular dyads [8e10], or polymers [11] have been described.…”