Solvent Tuning of the Optical Absorption and Fluorescence Properties of Meso-tetra(aryl)porphyrins and Their Dications With Weak and Strong Carboxylic Acids

Abstract

The solvent dependence of the photophysical properties of meso-tetra(aryl)porphyrins with electron-donating and electron-withdrawing meso substituents and their dications with CF 3 COOH and CH 2 ClCOOH has been studied. Dependence of the natural radiative lifetimes (t 1 , t 2, t 3 ), non-radiative rate constant (k nr ), fluorescence quantum yields (F f ), stokes shifts and the intensity of the emission bands of the free base porphyrins and the dications on the solvent polarity and Lorentz-Lorenz function, F(n 2 ) = (n 2 -l)/(n 2 + 2) (n, refractive index) was investigated in details. Furthermore, the degree of configuration interaction (CI) between the excited states was evaluated from the f Soret /f Q(0,0) ratio. It was found that the optical absorption and fluorescence characteristics of the free base porphyrins and their diacids can be finely tuned by changing the solvent's polarity, even though no close correlation was observed between some of the optical properties and the solvent properties.

Significantly Increased Stability of Donor–Acceptor Molecular Complexes under Heterogeneous Conditions: Synthesis, Characterization, and Photosensitizing Activity of a Nanostructured Porphyrin–Lewis Acid Adduct

“…It should be noted that the molecular complexation of porphyrins with different acceptors and the concomitant saddling of the porphyrin core increase the polarity of the aromatic macrocycle, leading to an increased solubility in polar solvents. The same pattern was observed upon diprotonation of porphyrins. ,,,,, …”

“…The two pyrrolenine nitrogen atoms of porphyrin macrocycles have lone pairs of electrons with a pK b of 9, which can be protonated easily with a wide range of acids. [32][33][34]48,49 Although the monoprotonated species of some porphyrins may be stabilized under special conditions such as polar solvents (e.g., nitrobenzene 50 ) and saddledistorted porphyrins (e.g., dodecaphenylporphyrins 51 ), no monoprotonated species was detected in weak polar organic solvents such as chloroform and dichloromethane. The reaction of porphyrins with BF 3 was shown to give a 1:2 molecular complex as the sole product.…”

“…The same pattern was observed upon diprotonation of porphyrins. 12,13,17,18,41,49 The molecular complexation of H 2 TMPyP with BF 3 led to the appearance of the absorption bands of the corresponding molecular complex at 443 and 652 nm (Figure 3). The addition of different equivalents of BF 3 (0.5−2) gradually increases the intensity of the Soret and Q bands.…”