Synthesis of Fluorescent Promazines and Evaluation of Photophysical Properties

Author

Jack James Pertile, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2019

Degree Name

Master of Science

Department

Chemistry

First Advisor

Hou, Yuqing

Abstract

A new series of fluorescent prorin (promazine-coumarin hybrid) derivatives were synthesized via piperidine catalyzed cyclization with 3-formyl-2-hydroxypromazine and ethyl acetoacetate or Meldrum’s acid. The synthesis of these new compounds focused on the introduction of electron withdrawing carbonyl groups on the 3-position of the coumarin lactone ring in order to increase polarization of the molecule which results in a longer absorbance wavelength by stabilizing intramolecular charge transfer that occurs in the excited state. The 3-acetyl derivative was further subjected to an aldol condensation with either benzaldehyde or cinnamaldehyde in order to further extend the conjugation of the molecule. The four new prorin compounds exhibited excellent photophysical properties and had Stokes shifts ranging from 160-190 nm. These properties are ideal for use as fluorescent probes to detect RNA binding ligands. The optical properties of the new prorin compounds were compared with a previous series of prorins as well as theoretical calculations in order to gain a more comprehensive understanding of how the photophysical properties of the molecule can be tuned by introducing different substituents. Although increasing polarization of the molecule with electron withdrawing substituents does red-shift the absorbance wavelength, it has little effect on the emission wavelength and can actually cause a blue-shift in some cases. It was observed that introducing aromatic substituents has the greatest effect on red-shifting the emission wavelength and increasing Stokes shift.