Photostable Voltage-Sensitive Dyes Based on Simple, Solvatofluorochromic, Asymmetric Thiazolothiazoles

Abstract

A family of asymmetric thiazolo [5,4-d]thiazole (TTz) fluorescent dye sensors has been developed, and their photophysical sensing properties are reported. The π-conjugated, TTz-bridged compounds are synthesized via a single-step, double condensation/ oxidation of dithiooxamide and two different aromatic aldehydes: one with strong electron-donating characteristics and one with strong electron-accepting characteristics. The four reported dyes include electron-donating moieties (N,N-dibutylaniline and N,N-diphenylaniline) matched with three different electron-accepting moieties (pyridine, benzoic acid, and carboxaldehyde). The asymmetric TTz derivatives exhibit strong solvatofluorochromism with Stokes shifts between 0.269 and 0.750 eV (2270 and 6050 cm −1 ) and transition dipole moments (Δμ = 13−18 D) that are among the highest reported for push−pull dyes. Fluorescence quantum yields are as high as 0.93 in nonpolar solvents, and the fluorescence lifetimes (τ F ) vary from 1.50 to 3.01 ns depending on the solvent polarity. In addition, thermofluorochromic studies and spectrophotometric acid titrations were performed and indicate the possibility of using these dyes as temperature and/or acid sensors. In vitro cell studies indicate good cell membrane localization, negligible cytotoxicity, promising voltage sensitivities, and photostabilities that are 4 times higher than comparable dyes. Their ease of synthesis and purification, remarkable photophysical properties, and chemically sensitive TTz π-bridge make these asymmetric dye derivatives attractive for environmental and biological sensing or similar molecular optoelectronic applications.

Relief of excited-state antiaromaticity enables the smallest red emitter

“…31 ) 52 , the excited-state dipole moments of p -DAPA and 5 are estimated to be 5.1 D and 6.0 D, respectively, which are substantially lower than those of typical ICT fluorophores (~ 20 D) 5 , 16 . Structurally related SBFs 29 – 32 also exhibit the characteristics of solvent-independent emission and small dipole moment in the excited-state, which are distinct from typical ICT fluorescence 5 , 16 . To demonstrate the general applicability of our mechanistic model, the same computational protocols were employed to probe the ground- and excited-states of amino–sulfonyl 30 , and amino–ester 31 SBFs (Supplementary Fig.…”

“…Based on the Lippert–Mataga equation (Supplementary Fig. 31 ) 52 , the excited-state dipole moments of p -DAPA and 5 are estimated to be 5.1 D and 6.0 D, respectively, which are substantially lower than those of typical ICT fluorophores (~ 20 D) 5 , 16 . Structurally related SBFs 29 – 32 also exhibit the characteristics of solvent-independent emission and small dipole moment in the excited-state, which are distinct from typical ICT fluorescence 5 , 16 .…”

“…Existing strategies to realize large Stokes shift rely on (i) intramolecular charge transfer (ICT) 5 , 6 , 16 , (ii) excited-state intramolecular proton transfer (ESIPT) 17 – 19 , (iii) fluorescence resonance energy transfer (FRET) 20 , 21 , (iv) desymmetrization of the molecular structure 6 , 22 – 24 , (v) excimer/exciplex emission 25 , or (vi) excited-state planarization of the benzannelated 8π system 26 – 28 . These design principles are applicable to known fluorogenic motifs, but often compromise other photophysical properties such as emission quantum yield.…”

Obtaining Reversible, High Contrast Electrochromism, Electrofluorochromism, and Photochromism in an Aqueous Hydrogel Device Using Chromogenic Thiazolothiazoles

“…[ 19 ] In addition, environmentally sensitive asymmetric TTz derivatives can serve as molecular probes for cell imaging and cell membrane voltage sensing. [ 33 ] The excellent electronic and optical properties of TTz‐based materials have enabled them to be studied in a variety of molecular electronic applications such as organic photovoltaics (OPVs), [ 34 ] organic field‐effect transistors (OFETs), [ 35–37 ] organic light‐emitting diodes (OLEDs), [ 38 ] metal‐organic framework/covalent‐organic framework materials, [ 39–42 ] and redox flow batteries. [ 43 ] Herein, multifunctional chromogenic devices (CGDs) (electrochromic, EFC, and photochromic) are demonstrated using extended TTz viologens developed for low cost, non‐toxic, and water‐based hydrogel devices.…”

A Silicon-Rhodamine Chemical-Genetic Hybrid for Far Red Voltage Imaging from Defined Neurons in Brain Slice

“…Voltage imaging in the central nervous system promises to transform the ways in which we observe brain systems. [1][2] Recently, a number of approaches to voltage imaging have emerged, including methods that rely solely on synthetic dyes [3][4][5][6][7][8][9] or genetically encoded proteins. [10][11][12][13][14][15][16][17] Alternatively, hybrid methodologies can combine the unique properties of synthetic dyes-high molecular brightness, wide availability of colors, or fast response kinetics-with the cellular specificity of genetically encoded methods.…”