Near-Infrared BODIPY-Acridine Dyads Acting as Heavy-Atom-Free Dual-Functioning Photosensitizers.

Boron dipyrromethene (BODIPY) dyes represent a particular class within the broad array of potential photosensitizers. Their highly fluorescent nature opens the door for theragnostic applications, combining imaging and therapy using a single, easily synthesized chromophore. However, near-infrared absorption is strongly desired for photodynamic therapy to enhance tissue penetration.

Absorption and Fluorescence Features of an Amphiphilic meso-Pyrimidinylcorrole: Experimental Study and Quantum Chemical Calculations.

Corroles are emerging as an important class of macrocycles with numerous applications because of their peculiar photophysical and metal chelating properties. meso-Pyrimidinylcorroles are easily deprotonated in certain solvents, which changes their absorption and emission spectra as well as their accessible supramolecular structures. To enable control over the formation of supramolecular structures, the dominant corrole species, i.

Origin of the Individual Basicity of Corrole NH-Tautomers: A Quantum Chemical Study on Molecular Structure and Dynamics, Kinetics, and Thermodynamics.

Free-base corroles exist as individual NH-tautomers that may differ in their spectral and chemical properties. The present paper focuses on the origin of the basicity difference between two AB2-pyrimidinylcorrole NH-tautomers, which has been tentatively attributed to differences in the weak out-of-plane distortions of the pyrrolenic ring between two NH-tautomers. Using DFT-geometry optimizations, we show that the pyrroles involved in the NH-tautomerization process are approximately in-plane, whereas the other two pyrroles are tilted out-of-plane in opposite directions.

Quantum chemical insights into the dependence of porphyrin basicity on the meso-aryl substituents: thermodynamics, buckling, reaction sites and molecular flexibility.

The chemical and sensing properties of porphyrins are frequently tuned via the introduction of peripheral substituents. In the context of the exceptionally fast second protonation step in the case of 5,10,15,20-tetraphenylporphyrin (TPP), as compared to porphin and 5,10,15,20-tetramesitylporphyrin (TMesP), we investigated the macrocycle-substituent interactions of these three porphyrin derivatives in detail. Using quantum chemical thermodynamics calculations, the analysis of geometric structures, torsional profiles, electrostatic potential distributions, and particularly the analysis of molecular flexibilities via ab initio molecular dynamics simulations, we obtained a comprehensive picture of the reactivities of the studied porphyrins and how these are influenced by the meso-substituents.

Molecular structures and absorption spectra assignment of corrole NH tautomers.

The individual absorption spectra of the two NH tautomers of 10-(4,6-dichloropyrimidin-5-yl)-5,15-dimesitylcorrole are assigned on the basis of the Gouterman four-orbital model and a quantum chemical TD-DFT study. The assignment indicates that the red-shifted T1 tautomer is the one with protonated pyrrole nitrogen atoms N(21), N(22) and N(23), whereas the blue-shifted T2 tautomer has pyrrole nitrogen atoms N(21), N(22) and N(24) protonated. A wave-like nonplanar distortion of the macrocycle in the ground state is found for both NH tautomers, with the wave axis going through the pyrroles containing N(22) and N(24).

Solvent-dependent deprotonation of meso-pyrimidinylcorroles: absorption and fluorescence studies.

The absorption spectra of 10-(4,6-dichloropyrimidin-5-yl)-5,15-dimesitylcorrole have been studied in 15 solvents. The formation of deprotonated corrole species was found to account for the dramatic changes in the absorption spectra in several solvents. Careful analysis of the relationship between the formation of deprotonated species and solvent properties results in the conclusion that there is no single solvent parameter correlation, and either multiparameter correlations or specific solute-solvent interactions (preferential solvation of the most acidic NH tautomer or perturbation of intramolecular hydrogen bonding in the macrocycle core) should be considered.

Unraveling the fluorescence features of individual corrole NH tautomers.

The fluorescence spectra of 10-(4,6-dichloropyrimidin-5-yl)-5,15-dimesitylcorrole have been studied in the temperature range from 4.2 to 332 K. For the first time, the individual fluorescence profiles of the two corrole NH tautomers have been assigned over the whole temperature range.

Corrole NH tautomers: spectral features and individual protonation.

Protonation of a free-base meso-pyrimidinyl-substituted AB(2)-corrole (H(3)AB(2)) in ethanol solution by stepwise addition of sulfuric acid has been studied in the temperature range from 293 to 333 K. The formation rate of protonated species was found to depend profoundly on the temperature at which the titration was undertaken. Two steps in the titration curve were identified at temperatures around 293-298 K, whereas one-step formation of protonated species was found to occur at temperatures above 308 K.

Structural volume changes upon triplet formation of water-soluble porphyrins depend on the resonant effect of the substituents.

Laser-induced optoacoustic spectroscopy was applied to evaluate the photoinduced structural volume changes upon triplet state formation, Δ(T)V, of an aqueous solution of 5,10,15,20-tetrakis-(4-carboxyphenyl)-porphin. Two molecular forms differing in the ionization state of the carboxylic groups at the para-position of the phenyl ring were studied. The contractions, Δ(T)V, for all water-soluble 5,10,15,20-tetra-aryl-porphyrin compounds studied to date show a linear correlation with the Hammett resonant σ(R) constant.

Luminescence of meso-pyrimidinylcorroles: relationship with substitution pattern and heavy atom effects.

The luminescence properties of a series of corroles containing multiple meso-pyrimidinyl groups have been studied. In particular, nine corroles containing two pyrimidinyl moieties, four corroles containing three pyrimidinyl groups and one corrole carrying a single pyrimidinyl substituent have been investigated, and their properties have been compared with some model species. The results indicate that the energy of the emissive π-π* corrole-core-based state is not significantly perturbed by the various substituents, whereas the emission lifetimes and quantum yields depend on the number of appended meso-dichloropyrimidinyl substituents.

Acid-base equilibria in 5,10,15,20-tetrakis(4-sulfonatophenyl)chlorin: Role of conformational flexibility.

The acid-base equilibria in 5,10,15,20-tetrakis(4-sulfonatophenyl)chlorin were studied in aqueous solution and compared with the respective data for the corresponding porphyrin. The reduction of the pyrrole ring in the tetrapyrrolic macrocycle noticeably influences both free base/monoprotonated and mono-/diprotonated species equilibria. In strong acidic solutions protonation of 4-sulfonatophenyl groups takes place in addition to protonation of the macrocycle core.