Mateusz Gierszewski

Acid–Base Equilibriums of Lumichrome and its 1-Methyl, 3-Methyl, and 1,3-Dimethyl Derivatives

Lumichrome photophysical properties at different pH were characterized by UV-vis spectroscopy and steady-state and time-resolved fluorescence techniques, in four forms of protonation/deprotonation: neutral form, two monoanions, and dianion. The excited-state lifetimes of these forms of lumichrome were measured and discussed. The results were compared to those obtained for similar forms of alloxazine and/or isoalloxazine, and also to those of 1-methyl- and 3-methyllumichrome and 1,3-dimethyllumichrome. The absorption, emission, and synchronous spectra of lumichrome, 1-methyl- and 3-methyllumichrome, and 1,3-dimethyllumichrome at different pH were measured and used in discussion of fluorescence of neutral and deprotonated forms of lumichrome. The analysis of steady-state and time-resolved spectra and the DFT calculations both predict that the N(1) monoanion and the N(1,3) dianion of lumichrome have predominantly isoalloxazinic structures. Additionally, we confirmed that neutral lumichrome exists in its alloxazinic form only, in both the ground and the excited state. We also confirmed the existence and the alloxazinic structure of a second N(3) monoanion. The estimated values of pK(a) = 8.2 are for the equilibrium between neutral lumichrome and alloxazinic and isoalloxazinic monoanions, with proton dissociation from N(1)-H and N(3)-H groups proceeding at the almost the same pH, while the second value pK(a) = 11.4 refers to the formation of the isoalloxazinic dianion in the ground state.

Spectroscopy and Photophysics of Monomethyl-Substituted Derivatives of 5-Deazaalloxazine and 10-Ethyl-5-Deaza-Isoalloxazine

Steady-state and time-resolved spectra were used to describe the singlet and triplet states of 8-methyl-5-deazaalloxazine (8-Me-5-DAll), 9-methyl-5-deazaalloxazine (9-Me-5-DAll) and 10-ethyl-5-deaza-isoalloxazine (10-Et-5-DIAll). Solvatochromic properties were described using different polarity scales, including Δf and the four-parameter scale proposed by Catalán. The results indicate that the Catalán scale shows a strong influence of solvent acidity (hydrogen-bond donating ability) on the emission properties of 8-Me-5-DAll and 9-Me-5-DAll. These results indicate the importance of intermolecular solute-solvent hydrogen-bonding interactions in the excited state of these compounds. Contrary to deazaalloxazines, solvent acidity affects the absorption spectra of 10-Et-5-DIAll. Fluorescence lifetimes and quantum yields and also transient absorption spectra were determined for all of the compounds studied. Electronic structure and S0-Si, S0-Ti, T1-Ti transitions energies and oscillator strengths were calculated using the TD-DFT methods. Theoretical calculations were compared to experimental data.

Photophysics, excited-state double-proton transfer and hydrogen-bonding properties of 5-deazaalloxazines.

The photophysical properties of 5‐deazaalloxazine and 1,3‐dimethyl‐5‐deazaalloxazine were studied in different solvents. These compounds have higher values of fluorescence quantum yields and longer fluorescence lifetimes, compared to those obtained for their alloxazine analogs. Electronic structure and S0–Si transitions were investigated using the ab initio methods [MP2, CIS(D), EOM‐CCSD] with the correlation‐consistent basis sets. Also the time‐dependent density functional theory (TD‐DFT) has been employed. The lowest singlet excited states of 5‐deazaalloxazine and 1,3‐dimethyl‐5‐deazaalloxazine are predicted to have the π, π* character, whereas similar alloxazines have two close‐lying π, π* and n, π* transitions. Experimental steady‐state and time‐resolved spectral studies indicate formation of an isoalloxazinic excited state via excited‐state double‐proton transfer (ESDPT) catalyzed by an acetic acid molecule that forms a hydrogen bond complex with the 5‐deazaalloxazine molecule. Solvatochromism of both 5‐deazaalloxazine and its 1,3‐dimethyl substituted derivative was analyzed using the Kamlet–Taft scale and four‐parameter Catalán solvent scale. The most significant result of our studies is that the both scales show a strong influence of solvent acidity (hydrogen bond donating ability) on the emission properties of these compounds, indicating the importance of intermolecular solute–solvent hydrogen‐bonding interactions in their excited state.

Effects of Post-Assembly Molecular and Atomic Passivation of Sensitized Titania Surface: Dynamics of Electron Transfer Measured from Femtoseconds to Seconds

The dynamics of electron transfer at the dye-titania and titania-electrolyte interfaces is investigated in two post-sensitization processes: (i) atomic layer deposition of blocking alumina coating and (ii) hierarchical molecular multicapping. To measure the electron transfer dynamics, time-resolved spectroscopic methods (femtosecond transient absorption on the time scale from femtoseconds to nanoseconds and electrochemical impedance spectroscopy on the time scale from milliseconds to seconds) are applied to the complete dye-sensitized solar cells with cobalt-based electrolyte and champion ADEKA-1 dye (with silyl-anchor unit) or its popular carboxyl-anchor analogue, MK-2 dye. Both molecular capping and alumina blocking layers slow down the electron injection process (the average rate constant decreases from 1.1 ps-1 to 0.4 ps-1) and partial sub-nanosecond back electron transfer from titania to the dye (from ca. 10 ns-1 to 5 ns-1). Very small alumina layers (of 0.1 nm thickness) have the highest impact on reducing the rate constants of these electron transfer processes, and for the thicknesses greater than 0.3 nm the rate constants hardly change. In contrast, the electron recombination between titania and electrolyte, occurring on the millisecond time scale, starts to be significantly suppressed for the blocking layers of 0.3 nm or more in thickness (up to ca. 20 times for 0.5 nm thickness with respect to that for untreated sample), improving open circuit voltage and fill factor of the cells. The amplitude of the relative photocurrent (short circuit current per number of absorbed photons) is found to depend almost exclusively on the ultrafast and fast processes taking place in the first nanoseconds after dye excitation. The positive impact of coadsorbents on the solar cells performance for both ADEKA-1 and MK-2 is also studied.

Photodynamic inactivation of Enterococcus faecalis by non-peripherally substituted magnesium phthalocyanines entrapped in lipid vesicles

Photophysical properties and photodynamic antibacterial potential of magnesium phthalocyanines bearing 2-propoxy, benzyloxy, 3,5-bis(benzyloxy)benzyloxy substituents at non-peripheral positions were studied. The UV-Vis absorption spectra of researched phthalocyanine derivatives were found typical. Extension of peripheral substituent size from 2-propoxy to benzyloxy and finally 3,5-bis(benzyloxy)benzyloxy was accompanied by the rise of quantum yield of fluorescence up to 0.17 and 0.04 in DMF and DMSO, respectively. Similarly, the expansion of the phthalocyanine periphery from the 2-propoxy to benzyloxy and 3,5-bis(benzyloxy)benzyloxy groups resulted in a detectable increase of the singlet oxygen quantum yield values to 0.04, 0.12, 0.14 respectively, which was assessed following direct method of singlet oxygen phosphorescence measurement at 1270 nm. Studied phthalocyanines undergo photobleaching process with the quantum yields at the level of 10-6 in DMSO and 10-5 in DMF. The size of phthalocyanine impacted the process of liposomal formulation. Small liposome vesicles containing non-peripherally substituted phthalocyanines with 2-propoxy and benzyloxy substituents were obtained following extrusion method. The unification process of the liposomes loaded with 3,5-bis(benzyloxy)benzyloxy non-peripherally substituted phthalocyanines was not possible. In in vitro antimicrobial photodynamic inactivation study, log reduction values of bacterial (Enterococcus faecalis) growth at 3.61 and 2.99 were achieved for liposomal formulations containing phthalocyanines with 2-propoxy and benzyloxy substituents respectively, whereas phthalocyanine with 3,5-bis(benzyloxy)benzyloxy substituents was inactive. Phthalocyanine with 2-propoxy substituents exhibited relatively low toxicity in Vibrio fischeri bioluminescence test, whereas phthalocyanine with benzyloxy substituents revealed intense bioluminescence, which could be associated with hormesis phenomenon.