Synthesis and spectroscopic characterization of two tetrasubstituted cationic porphyrin derivatives

Abstract

An imidazolium tetrasubstituted cationic porphyrin derivative (the free base and its Zn(II) complex) with five-membered heterocyclic groups in the meso-positions were synthesized using microwave irradiation, and the compounds obtained characterized by (1)H-NMR and mass spectrometry. We observed that under microwave irradiation the yield is similar to when the synthesis is performed under conventional heating, however, the time required to prepare the porphyrins decreases enormously. In order to investigate the electronic state of these compounds, we employed UV-Vis and fluorescence spectroscopy combined with quantum chemical calculations. The results reveal the presence, in both compounds, of a large number of electronic states involving the association between the Soret and a blue-shifted band. The Soret band in both compounds also shows a considerable solvent dependence. As for emission, these compounds present low quantum yield at room temperature and no solvent influence on the fluorescence spectra was observed.

Figure 1

Representation of the molecular structures: (a) [H₂-TDMImP]I₄; (b) [Zn(TDMImP)]I₄.

Figure 2

MALDI TOF/TOF spectrum for Zn(TDMImP).

Figure 3

(a) Absorption (black line) and fluorescence (red line) spectra of H₂-TDMImP, at 298 K; (b) Absorption (black line) and fluorescence (red line) spectra of Zn(TDMImP), at 298 K.

Figure 4

State diagram for Zn(TDMImP). The inset shows the state diagram for H₂-TDMImP. These diagrams were calculated in ethanol (TD-DFT/IEFPCM) using symmetry constraints. Red lines stands for singlet states, black lines stands for triplet states.

Figure 5

Representation of the TD-DFT UV-Vis excitation spectrum of Zn(TDMImP) (a), and H₂-TDMImP (b), calculated under a SCRF procedure (IEFPCM, solvent = ethanol).

Scheme 1

Schematic view of the synthetic route adopted in this work for porphyrin synthesis.