Fluorescence of Hydroxyphenyl-Substituted “Click” Triazoles

Abstract

The structural and optical properties of hydroxyphenyl-substituted-1,2,3-triazole molecules ("click" triazoles) are described. "Click" triazoles are prepared from the copper(I)-catalyzed azide-alkyne cycloaddition reactions. The alkyne-derived C4 substituent of a "click" triazole engages in electronic conjugation more effectively with the triazolyl core than the azide-derived N1 substituent. Furthermore, triazolyl group exerts a stronger electron-withdrawing effect on the N1 than the C4 substituent. Therefore, the placement of an electron-donating group at either C4 or N1 position and the presence or the absence of an intramolecular hydrogen bond (HB) have profound influences on the optical properties of these compounds. The reported "click" triazoles have fluorescence quantum yields in the range of 0.1-0.3 and large apparent Stokes shifts (8000-13 000 cm) in all tested solvents. Deprotonation of "click" triazoles with a C4 hydroxyphenyl group increases their Stokes shifts; while the opposite (or quenching) occurs to the triazoles with an N1 hydroxyphenyl substituent. For the triazoles that contain intramolecular HBs, neither experimental nor computational results support a model of excited state intramolecular proton transfer (ESIPT). Rather, the excited state internal (or intramolecular) charge transfer (ICT) mechanism is more suitable to explain the fluorescence properties of the hydroxyphenyl-substituted "click" triazoles; specifically, the large Stokes shifts of these compounds.

The revelation of ESIPT behavior and fluoride response mechanism for (E)‐2‐(((1H‐benzo[d]imidazol‐2‐yl)‐imino)methyl)‐5‐(dimethylamino)‐phenol

“…Furthermore, the hydrogen bond strengthening or weakening could also be revealed based on monitoring the spectral shifts of vibrational modes involved in the formation of hydrogen bonds . The vibrational spectra of bip chromophore in the conjunct vibrational regions of the O‐H stretching mode have been shown in Figure .…”

“…The geometric optimizations of bip , bip‐open and bip‐pt were performed using DFT in the S 0 state and using TDDFT in the S 1 state. Especially, the TDDFT method has become a very useful tool to theoretically investigate the hydrogen bonding interaction that occurs in the excited states . In addition, Becke's three‐parameter hybrid exchange functional with Lee–Yang–Parr gradient‐corrected correlation (B3LYP functional) was selected in both the DFT and TDDFT methods .…”

“…Till now, many different sensing mechanisms, such as intramolecular charge transfer (ICT), photo‐induced electron transfer (PET), fluorescence resonance energy transfer (FRET), and excited state proton transfer (ESPT) and so forth, are relevant with intra‐ or inter‐ molecular hydrogen bond. Particularly, the excited state inter‐ and intra‐ molecular proton transfer (ESIPT) reactions have been drawing great attention due to their unique photo‐physical and photo‐chemical properties.…”

“…Even though this sensor has weak fluorescence, it was reported that the anion‐binding adduct of bip is expected to be highly fluorescent based on ESIPT channel experimentally, however, the mechanism of bip in excited state is very limitted. In effect, experimental spectroscopic techniques, such as steady‐state absorption spectroscopy, fluorescence spectroscopy and time resolved fluorescence spectroscopy, just provide the indirect information about photo‐physical and photo‐chemical properties . Up to now, the theoretical investigations about the bip are very scarce in addition to the experiments.…”

Click-chemistry enabled directed evolution of glycosynthases for bespoke glycans synthesis

“…Recent studies have suggested that the alkyne-derived substituent moiety of a "click" triazole can engage in electronic conjugation with the triazolyl core that may have profound influences on the optical properties of these compounds. 50 Photon reabsorption behavior of such compounds can be vexing for the development of energy efficient lightemitting materials, however, this could be advantageous for producing a composite emission color that facilitates selective detection of differentially substitutes triazole products during SPAAC reactions. The influence of the triazole moiety substitution patterns on the electrochemical and photophysical properties of the donor-acceptor groups has been reported in the literature.…”