Computational Prediction and Experimental Evaluation of a Photoinduced Electron-Transfer Sensor

Abstract

An approach is presented for the design of photoinduced electron-transfer-based sensors. The approach relies on the computational and theoretical prediction of electron-transfer kinetics based on Rehm-Weller and Marcus theories. The approach allows evaluation of the photophysical behavior of a prototype fluorescent probe/sensor prior to the synthesis of the molecule. As a proof of concept, a prototype sensor for divalent metal ions is evaluated computationally, synthesized, and then analyzed spectroscopically for its fluorescence response to zinc. Calculations predicted that the system would show a competition between electron transfer and fluorescence in the free state. In the zinc-bound state, the compound was predicted to be more highly fluorescent, due to the inhibition of electron transfer. Both predictions were confirmed experimentally. A nonzero fluorescence signal was observed in the absence of zinc and an enhancement was observed in the presence of zinc. Specifically, a 56-fold enhancement was observed over a 10-fold increase in zinc concentration.

Tuning electron–hole distance of the excitons in organic molecules using functional groups

“…All the excitons discussed here have an e − -h + distance of more than 2Å, which are different from the excitons generated in, for instance, anthracene [32,33], where the HOMO and LUMO completely overlap and the e − -h + distance is expected to be very small. The current study suggests that the donor molecules MTPAo, MTPAcl, and MTPAc are all promising donor modula for organic photovoltaics, in addition to MTPA and MTPAa that were already being used.…”

Computational Studies on Response and Binding Selectivity of Fluorescence Sensors

“…The sensor in Fig. 1 differs slightly from the one discussed in the original work1 in that the linker of the current sensor has one more CH 2 . We expect, and as our study has also shown, that this minor difference would not affect any of the computational predictions.…”

“…Once the sensor candidates are selected computationally, they will then be synthesized, characterized, and subsequently refined. As a proof of concept, we have successfully developed a PET fluorescent sensor for detecting Zn 2+ using the new approach 1. The computational selection of the sensor candidates in that work is based on the comparison of the energies between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) of fluorophore, free receptor, and bound receptor using B3LYP/6-31G(d,p).…”

“…Using this proposed sensor as an example, we performed the Becke’s three-parameter exchange functional with the Lee-Yang-Parr correlation functional (B3LYP)15-18 and time-dependent B3LYP (TD-B3LYP) calculations with various basis sets to study the response and binding selectivity of the sensor for divalent Zn 2+ ions, in addition to develop a general computational sensor synthesis protocol. B3LYP has mainly been used to calculate structural parameters, energetics, and molecular orbital energies including the HOMO and LUMO energies 1,19-22. In the sensor design we are concerned with excited states of the fluorophore and the transitions to these excited states upon adsorption of photons, as these excited states and the transitions are important to understanding the fluorescent behavior of the sensor, both in the presence and absence of the target molecules.…”

Molecular Rotors as Fluorescent Viscosity Sensors: Molecular Design, Polarity Sensitivity, Dipole Moments Changes, Screening Solvents, and Deactivation Channel of the Excited States

“…[12,16] However, different from most D-π-A fluorophores, [19][20][21][22][23] the emission of the FMRs is not sensitive to the polarity of the solvent, [5] that is, the emission intensity and the emission wavelength will not change significantly by variation in the polarity of the solvents. [5,6,24] According to the traditional theory of FMRs, viscosity sensitivity and polarity sensitivity are two exclusive properties, that is, those rotors that show solvent-polarity-dependent emission will not show the FMR property and vice versa.…”