Synthesis and spectroscopic characterisation of new ESIPT fluorescent protein probes

Abstract

Three new benzazole isothiocyanate fluorescent dyes, 2-(4'-isothiocyanate-2'-hydroxyphenyl)benzoxazole, 2-(4'-isothiocyanate-2'-hydroxyphenyl)benzothiazole and 2-(4'-isothiocyanate-2'-hydroxyphenyl)benzimidazole were synthesised, purified until optical purity grade and characterised by spectroscopic techniques. UV/VIS and steady-state fluorescence were also applied to characterise the photophysical behaviour of the dyes. These dyes exhibit an intense fluorescence emission with a large Stokes shift, inherent to the class of benzazoles which relax by the excited state intramolecular proton transfer (ESIPT) mechanism. The dyes were studied for labeling bovine serum albumin (BSA), resulting conjugates BSA-dye with a remarkable photostability under UV/VIS radiation in relation to classical protein labels. The resulting conjugates presented fluorescence in the blue-green region. Direct fluorescence detection of protein-labeled with those dyes after polyacrylamide gel electrophoresis indicates their potential use as fluorescent probes for proteins.

New fluorescent monomers and polymers displaying an intramolecular proton‐transfer mechanism in the electronically excited state (ESIPT). IV. Synthesis of acryloylamide and diallylamino benzazole dyes and its copolymerization with MMA

“…New fluorescent acryloyl and allyl monomers were synthesized, purified until optical purity grade, and characterized by elemental analysis, 1 H NMR, 13 C NMR, IR, UV-vis, and steady-state fluorescence spectroscopy. The monomers are fluorescent in the bluegreen-yellow-red region and present a Stokes shift between 92 and 226 nm.…”

“…[1][2][3][4][5] This phenomenon has implications in the UV-light stabilizers field, 6,7 laser dyes, 8 new polymeric materials, 9 -12 and also as fluorescent probes to labeling proteins. 13,14 The ESIPT mechanism is quite dependent on the solvent polarity, [15][16][17] and many studies regarding this dependence, [17][18][19][20][21] as well as, theoretical calculations involving the geometry of the conformers in solution [22][23][24][25][26][27] have been made. In protic and/or polar solvents the enol-cis open conformer (E II ) can be stabilized by intermolecular hydrogen bond with the solvent.…”

Electronic and photophysical properties of 2-(2′-hydroxyphenyl)benzoxazole and its derivatives enhancing in the excited-state intramolecular proton transfer processes: A TD-DFT study on substitution effect

“…After decaying radiatively to the ground keto form (S 0 keto), the reverse PT takes place to give its initial enol form (Scheme 1). Because of their unique optical property given by ESIPT, HBO and its derivatives have been employed as luminescent material [11,12], chemical sensors for zinc(II) [13] and anions [14], light-emitting diode devices [15], optical switching [16,17], and fluorescent probe [18,19]. In general, fluorescence spectra of these molecules exhibit both enol and keto emission.…”

Novel ESIPT fluorescent benzazolyl-4-quinolones: Synthesis, spectroscopic characterization and photophysical properties

“…Intramolecular proton transfer occurs when a molecule contains both an acidic and a basic site which, upon electronic excitation, experience enhanced acidity or basicity, respectively [21] The excited keto tautomer (K 1 ) decays, therby emitting fluorescence as the fundamental keto tautomer (K 0 ), and the initial enol form (E 0 ) is regenerated [22,23]. Since most ESIPT processes are reversible, these systems have found application as UV-light stabilizers [24,25], laser dyes [26], sensors [27], DNA probes [28,29], in drug delivery systems [30], hybrid materials [31] and also as fluorescent probes [32][33][34][35].…”