Stilbene-Based Two-Photon Thermo- Solvatochromic Fluorescence Probes with Large Two-Photon Absorption Cross Sections and Two- Photon Triple Fluorescence: Detection of Solvent Polarities, Viscosities, and Temperature

Chi Bao Huang

doi:10.34297/ajbsr.2019.04.000778

Abstract

The unusually sensitive solvatochromism of 2,5-dicyano-4-methyl-4’-dimethylaminostilbene (P1) whose emission maximum varies from 445 nm in cyclohexane to 641 nm in DMSO are described. 1a with remarkably large two-photon cross sections exhibits very strong polarity-, viscosity-, and temperature-dependence of fluorescence, and can be used to detect polarities, viscosities, and temperature. The successful application of P1 provides a brilliant prototype for the developments of ideal two-photon fluorescence probes.

Highlights

For the development of two-photon (TP) fluorescence (TPF)optimized molecular probes, it is important to have a significant modulation of the photophysical properties of the chromophore in response to external stimuli, such as polarity, pH, ion concentration, and temperature
In contrast to PET-based fluorescence probes, which only show increasing or decreasing emission intensity at fixed wavelength, solvatochromic probes may indicate the presence of an analyte by a significant change of emission wavelength [1] which is unequivocally detectable
We report two TP solvatochromic probes (P1 and P2) derived from 4-methyl-2,5-dicyano-4’-amino stilbene (DCS) with remarkably large δ, which has been successfully employed in the design of TPF probes for metal ions

Summary

Introduction

For the development of two-photon (TP) fluorescence (TPF)optimized molecular probes, it is important to have a significant modulation of the photophysical properties of the chromophore in response to external stimuli, such as polarity, pH, ion concentration, and temperature. In the excited state, the adiabatic ICT leads to an intermediate that most likely develops a negative charge for the nitrogen atom of the orthocyano group, that is, after solvent relaxation [6,12,13] stabilized by polar solvents, especially those with high π*, and by the meta-cyano group with strong electron-withdrawing capacity for greater diffusion of the concentrated negative charge This ICTsolvent relaxation sequence explains the significant red shift of the emission spectra in polar solvents as well as the temperature and viscosity dependence of the emission properties [6,13]

Materials and Methods

Conclusion