Rational Design of d-PeT Phenylethynylated-Carbazole Monoboronic Acid Fluorescent Sensors for the Selective Detection of α-Hydroxyl Carboxylic Acids and Monosaccharides

Abstract

We have synthesized three new phenylethynylated carbazole boronic acid sensors, which were predicted to display novel d-PeT fluorescence transduction (PeT, photoinduced electron transfer; fluorophore as the electron donor of the electron transfer, ET) by DFT/TDDFT calculations. The d-PeT effect is characterized by a lower background fluorescence at acidic pH than at neutral pH, which is in stark contrast to the normal a-PeT effect (fluorophore as the electron acceptor of the ET) that shows a strong and undesired background fluorescence at acidic pH. Our experimental results confirmed the theoretical predictions and d-PeT was observed for two of the sensors (with p-dimethylaminophenylethynyl substitution at 6-position of the carbazole core). For the third sensor (with phenylethynyl substitution at 6-position of the carbazole core), however, not d-PeT but rather the normal a-PeT was observed. The discrepancy between the DFT/ TDDFT calculations and the experimental observations can be rationalized using free energy changes (Rehm-Weller equations) and the rate constants for the ET (k ET , Marcus equation). These new d-PeT boronic acid sensors show improved photophysical properties compared to the known d-PeT sensor reported previously by us. In particular, the fluorescence transduction efficiency of the new sensors was improved 8-fold when compared to the known d-PeT boronic acid sensors. Novel fluorescence enhancement/reduction was observed for one of the sensors upon binding with mandelic acid or tartaric acid at pH 5.6. The effect of pH as well as the bonding with analytes on the emission of the sensors were rationalized using DFT/ TDDFT calculations. We believe that rational sensor design aided by DFT/TDDFT calculations as well as using free energy changes and electron transfer rate constants to study the emission properties of PeT sensors will become an essential tool in the design of new fluorophores or fluorescent sensors with predetermined photophysical properties.

Theoretical Approach Towards Rational Design and Characterization of Benzo[1,2-b:5-B’]dithiophene (BDT)-Based (A-D-A) Small Molecules of Relevance for High Performance Solar Cells

“…For the heterojunction P3HT/PC 61 BM, the reorganization energy λ ext is 0.11 eV [39], so we admit a value of 0.11 eV for the λ ext in our calculations. The calculated total reorganization energy [67,68,71,[74][75][76]:…”

External Electric Field-Dependent Photoinduced Electron Transfer of Oligonaphthofurans-PC₇₀BM in BJH Solar Cell

“…For efficiently quenching an electronic transition excited state and competing with other non-radiation pathways, the exothermic situation is needed [26]. So far, the theoretical simulation of two major modalities ΔG CT and ΔG CR in different ways were used [25][26][27][28][29][30][31][32].…”

DFT and experimental studies on structure and spectroscopic parameters of 3,6-diiodo-9-ethyl-9H-carbazole

“…Carbazole derivatives have very interesting photoconductivity [10] and optical [11] properties. Due to their fluorescent ability, carbazoles are used for the production of light emitting diodes (OLEDs) [12,13] and sensors [14][15][16][17]. For these reasons, there is a constant search for new carbazole derivatives as potential substrates for new materials with promising optoelectronic properties.…”

“…Molecular modeling of NMR parameters is widely used to support assignments of experimental spectra [19][20][21]. Satisfactory chemical shifts for several different nuclei including 13 C, 17 O, 15 N and 19 F [19,[22][23][24][25] can be obtained by density functional theory calculations in combination with gauge including atomic orbitals (GIAO) [26,27] and employing the Becke, three-parameter, Lee-Yang-Parr (B3LYP) [27,28] or BHandHLYP hybrid half-and-half functional [29]. In particular the latter was used to predict accurate NMR parameters.…”