Synthesis, Spectroscopic Characterization, and Theoretical Modeling of a Resorufin-Bearing Pyrrole Derivative with a Dual Emission.

The present study reports the synthesis and spectroscopic characterization of a novel pyrrole derivative labeled with resorufin substituent. Steady-state photoluminescence of 3-(N-pyrrolyl)propyl resorufin (Py-Res) is investigated in solvents with distinct polarities. Our results show that medium polarity strongly affects the fluorescence spectrum of Py-Res, which is characterized by an unusual excitation-dependent dual emission involving distinct excited states. A detailed computational analysis of Py-Res is performed using time-dependent density functional theory (TD-DFT), which supplies information about the frontier orbitals involved in vertical absorption and emission energies. The results of quantum mechanical calculations show that the emission mechanism of Py-Res may include the formation of locally excited states or intramolecular charge transfer, depending on the solvent polarity. TD-DFT calculations support the experimental findings that the Py-Res fluorescence is associated with distinct excited states. The thermal effects on Py-Res emission are investigated, where a linear thermal-quenching is verified. Moreover, the possibility of using Py-Res photoluminescence to develop a ratiometric sensor for detecting ethanol adulteration with methanol is analyzed.