Investigation of Ground- and Excited-State Photophysical Properties of 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphyrin with Ruthenium Outlying Complexes

Abstract

The present work employs a set of complementary techniques to investigate the influence of outlying Ru(II) groups on the ground- and excited-state photophysical properties of free-base tetrapyridyl porphyrin (H(2)TPyP). Single pulse and pulse train Z-scan techniques used in association with laser flash photolysis, absorbance and fluorescence spectroscopy, and fluorescence decay measurements, allowed us to conclude that the presence of outlying Ru(II) groups causes significant changes on both electronic structure and vibrational properties of porphyrin. Such modifications take place mainly due to the activation of nonradiative decay channels responsible for the emission quenching, as well as by favoring some vibrational modes in the light absorption process. It is also observed that, differently from what happens when the Ru(II) is placed at the center of the macrocycle, the peripheral groups cause an increase of the intersystem crossing processes, probably due to the structural distortion of the ring that implies a worse spin-orbit coupling, responsible for the intersystem crossing mechanism.

Light-Driven Redox Activation of CO2- and H2-Activating Complexes in a Self-Assembled Triad

“…The electron-transfer rate constant associated with the oxidative quenching of the S 1 state cannot be determined because the native lifetime of the ZnP S 1 state in the absence of quenching is unknown. Assuming that the native lifetime for this subunit is that of ZnTPP (τ 0 = 1.7 ns in CH 2 Cl 2 ), and using τ S1 = 900 ps reported by Casanova et al, the overall rate constant for the processes that accelerate S 1 decay can be estimated using eq to be k q = 5.2 × 10 8 s –1 . This contains contributions from the heavy-atom effect (or other nonradiative processes facilitated by the Re center) and oxidative quenching. As will be developed later based on data for 1 , the quantum yield and rate constant for oxidative quenching may be estimated to be ∼0.002 and 1 × 10 6 s –1 , respectively, with these small values being consistent with the fact that the electron-transfer reaction is roughly thermoneutral (Δ G ≈ −0.05 V) and occurs between weakly coupled redox orbitals (ZnPor and bpy).…”

Modified glassy carbon electrode with AuNPs using cis-[RuCl(dppb)(bipy)(4-vpy)]+ as crossed linking agent

“…The bond distances and angles listed in the caption of the Fig. 2 4-methylpyridine and 4-phenylpyridine, as previously reported [33,39,43,44]. In all three complexes, the dissociated chloride was always the one trans to a phosphorus atom in the precursor cis-[RuCl 2 (P-P)(bipy)] or cis-[RuCl 2 (P-P)(5,5 0 -Me-bipy)] {where P-P = aromatic biphosphine}, as expected, given the stronger trans effect of the phosphorus atom and in accordance with the X-ray structures.…”

Studying the intersystem crossing rate and triplet quantum yield of meso-substituted porphyrins by means of pulse train fluorescence technique

“…The photodetector electrical signal was acquired by a 1 GHz oscilloscope and recorded by a computer. The procedure of measuring the sample fluorescence induced by pulse train is referred as pulse train fluorescence technique (PTF) [22], while the one using a single pulse is referred as time-resolved fluorescence technique (TRF).…”

“…For example, Gonçalves et al [20] demonstrated that the insertion of zinc in sulfonated porphyrin free-bases drastically reduced the ISC rate from 13 ns [21] to 2.2 ns [20]. Sampaio et al [22] have shown that free-base 5,10,15,20-tetra(4-pyridyl)porphyrin (H 2 TP y P) with ruthenium(II) ions bound at the peripheral groups of the macrocycle increases the ISC time about twofolds compared to porphyrins without Ru(II) (from 14 ns to 25 ns). This behavior is opposite to that of porphyrins with Ru(II) inserted in macrocycle core.…”