Zinc Porphyrin Research Articles

A Mo2-ZnP molecular device that mimics photosystem I for solar-chemical energy conversion

Bioinspired solar-chemical energy conversion has long been challenged by chemists with searching for effective synthetic photocatalysts. Herein we show that powered by visible light, molecular photocatalysts developed by integrating zinc porphyrin (ZnP) with a quadruply-bonded Mo2 unit enables hydrogen evolution from water in high yields up to 200 mmol g−1 with TON = 640. Remarkably, this unimolecular Mo2-ZnP device catalyzes efficiently photoreduction of nicotinamide adenine dinucleotide (NAD+) to NADH, the reducing equivalent for enzymatic reduction of CO2 in natural photosynthesis. Evidently, this Mo2-ZnP photosystem has the capability of accumulating up to four electrons and two protons for two-electron reduction. Mechanistic investigations reveal that the photoreduced zinc phlorin and chlorin-phlorin anions are the catalytic intermediates for hydride transfer to the substrates, which mimics functionally the hydroquinone state of flavin adenine dinucleotide in photosystem I. The understandings gained in this study are valuable for engineering photocatalysts for solar fuel production.

One-Photon Excitation Followed by a Three-Step Sequential Energy-Energy-Electron Transfer Leading to a Charge-Separated State in a Supramolecular Tetrad Featuring Benzothiazole-Boron-Dipyrromethene-Zinc Porphyrin-C60.

A panchromatic triad, consisting of benzothiazole (BTZ) and BF2 -chelated boron-dipyrromethene (BODIPY) moieties covalently linked to a zinc porphyrin (ZnP) core, has been synthesized and systematically characterized by using 1 H NMR spectroscopy, ESI-MS, UV-visible, steady-state fluorescence, electrochemical, and femtosecond transient absorption techniques. The absorption band of the triad, BTZ-BODIPY-ZnP, and dyads, BTZ-BODIPY and BODIPY-ZnP, along with the reference compounds BTZ-OMe, BODIPY-OMe, and ZnP-OMe exhibited characteristic bands corresponding to individual chromophores. Electrochemical measurements on BTZ-BODIPY-ZnP exhibited redox behavior similar to that of the reference compounds. Upon selective excitation of BTZ (≈290 nm) in the BTZ-BODIPY-ZnP triad, the fluorescence of the BTZ moiety is quenched, due to photoinduced energy transfer (PEnT) from 1 BTZ* to the BODIPY moiety, followed by quenching of the BODIPY emission due to sequential PEnT from the 1 BODIPY* moiety to ZnP, resulting in the appearance of the ZnP emission, indicating the occurrence of a two-step singlet-singlet energy transfer. Further, a supramolecular tetrad, BTZ-BODIPY-ZnP:ImC60 , was formed by axially coordinating the triad with imidazole-appended fulleropyrrolidine (ImC60 ), and parallel steady-state measurements displayed the diminished emission of ZnP, which clearly indicated the occurrence of photoinduced electron transfer (PET) from 1 ZnP* to ImC60 . Finally, femtosecond transient absorption spectral studies provided evidence for the sequential occurrence of PEnT and PET events, namely, 1 BTZ* -BODIPY-ZnP:ImC60 →BTZ-1 BODIPY* -ZnP:ImC60 →BTZ-BODIPY-1 ZnP* :ImC60 →BTZ-BODIPY-ZnP.+ :ImC60 .- in the supramolecular tetrad. The evaluated rate of energy transfer, kEnT , was found to be 3-5×1010 s-1 , which was slightly faster than that observed in the case of BODIPY-ZnP and BTZ-BODIPY-ZnP, lacking the coordinated ImC60 . The rate constants for charge separation and recombination, kCS and kCR , respectively, calculated by monitoring the rise and decay of C60 .- were found to be 5.5×1010 and 4.4×108 s-1 , respectively, for the BODIPY-ZnP:ImC60 triad, and 3.1×1010 and 4.9×108 s-1 , respectively, for the BTZ-BODIPY-ZnP:ImC60 tetrad. Initial excitation of the tetrad, promoting two-step energy transfer and a final electron-transfer event, has been successfully demonstrated in the present study.

A Light-Harvesting/Charge-Separation Model with Energy Gradient Made of Assemblies of meta-Pyridyl Zinc Porphyrins.

Self-assembly of porphyrins is a fascinating topic, not only for mimicking chlorophyll assemblies in photosynthetic organisms, but also for the potential of creating molecular-level devices. Herein, zinc porphyrin derivatives bearing a meta-pyridyl group at the meso position were prepared and their assemblies studied in chloroform. Among the porphyrins studied, one with a carbamoylpyridyl moiety gave a distinct 1 H NMR spectrum in CDCl3 , which allowed the supramolecular structure in solution to be probed in detail. Ring-current-induced chemical-shift changes in the 1 H NMR spectrum, together with vapor-pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer with a triangular cone structure. Incorporation of a directly linked porphyrin-ferrocene dyad with the same assembling properties in the assemblies led to a rare example of a light-harvesting/charge-separation system in which an energy gradient is incorporated and reductive quenching occurs.

Experimental and Theoretical Comparable Study of Pure and Zinc Porphyrin Surface Modified ZnO Nanorod Arrays for Hybrid Solar Cell Applications

Experimental and Theoretical Comparable Study of Pure and Zinc Porphyrin Surface Modified ZnO Nanorod Arrays for Hybrid Solar Cell Applications

Sustainable synthesis of multifunctional porous metalloporphyrin polymers for efficient carbon dioxide transformation under mild conditions

Multifunctionalization of porous organic polymers (POPs) for working in concert on a substrate is now a research topic in CO2 catalysis, yet it remains challenging. This work describes a pre- and post-synthetic strategy to design metalloporphyrin-based azo-hierarchical porous ionic polymers (ZnTPP/QA-azo-PiPs), which were synthesized based on diazo-coupling reaction of tetra(4-aminophenyl) porphyrin zinc with tri/diphenols in aqueous solution under mild conditions, followed by etherification with quaternary ammonium bromide. This synthetic approach endows ZnTPP/QA-azo-PiP1 with features of an improved surface area (181 m2/g), hierarchical porosity, and high-density active sites. ZnTPP/QA-azo-PiP1 presented a noteworthy CO2 uptake of 1.77 mmol/g at 273 K and 1.0 bar and good CO2/N2 selectivity of 44.8. As expected, ZnTPP/QA-azo-PiP1 showed quantitative conversion and selectivity for a range of epoxides under mild conditions (1.0 MPa, 80 °C, 12 h) in the CO2 cycloaddition reaction. ZnTPP/QA-azo-PiP1 could been recycled easily and retained complete retention of activity and selectivity for over 7 cycles. Moreover, with efficacious activity in conversion of diluted CO2 (15% CO2 in 85% N2, v/v), ZnTPP/QA-azo-PiP1 could smoothly catalyze CO2-involved reaction to produce oxazolidinones and N-formylated amines under mild conditions. This work promotes sustainable synthesis of advanced multifunctional POPs and gives great promise for their application in synthetic transformations of CO2.

Plasmon-enhanced S2 electroluminescence from the high-lying excited state of a single porphyrin molecule

We demonstrate the B-band electroluminescence from the high-lying S2 excited state of a single zinc porphyrin molecule with the scanning tunneling microscope-induced luminescence technique by using an aluminum tip. The nanocavity plasmon mode is found to be critical for the occurrence of S2 electroluminescence. When using a silver tip to excite the molecule electronically decoupled from the Ag(100) substrate by an ultrathin sodium chloride spacer, we only observe the Q-band electroluminescence originating from the radiative decay of the S1 first excited state, without any B-band emission due to the lack of effective plasmonic enhancement for the B-band. However, when the nanocavity plasmon resonance is tuned to a bluer range by using an aluminum tip, the S2 electroluminescence from a single zinc porphyrin shows up because the nanocavity plasmon mode can now spectrally overlap with the B-band emission to generate efficient plasmonic enhancement for the radiative decay directly from the S2 state. Interestingly, the excitation mechanisms for these two types of emission are found to be different. While the Q-band emission is attributed mainly to a carrier-injection mechanism, the B-band electroluminescence is found to be excited via an inelastic electron scattering process. Our results open a route to investigate the photophysical property and dynamic behavior of isolated molecules in their excited states.

Experimental and Theoretical Comparable Study of Pure and Zinc Porphyrin Surface Modified ZnO Nanorod Arrays for Hybrid Solar Cell Applications

Experimental and theoretical study Porphyrin-grafted ZnO nanowire arrays were investigated for organic/inorganic hybrid solar cell applications. Two types of porphyrin – Tetra (4-carboxyphenyle) TCPP and meso-Tetraphenylporphine (Zinc-TPP)were used to modify the nanowire surfaces. The vertically aligned nanowires with porphyrin modifications were embedded in graphene-enriched poly (3-hexylthiophene) [G-P3HT] for p-n junction nanowire solar cells. Surface grafting of ZnO nanowires was found to improve the solar cell efficiency. There are different effect for the two types of porphyrin as results of Zn existing. Annealing effects on the solar cell performance were investigated by heating the devices up to 225 °C in air. It was found that the cell performance was significantly degraded after annealing. The degradation was attributed to the polymer structural change at high temperature as evidenced by electrochemical impedance spectroscopy measurements.

A Cationic Porphyrin, ZnPor, Disassembles Pseudomonas aeruginosa Biofilm Matrix, Kills Cells Directly, and Enhances Antibiotic Activity of Tobramycin.

One of the greatest threats to human health is the rise in antibiotic-resistant bacterial infections. Pseudomonas aeruginosa (PsA) is an “opportunistic” pathogen known to cause life-threatening infections in immunocompromised individuals and is the most common pathogen in adults with cystic fibrosis (CF). We report here a cationic zinc (II) porphyrin, ZnPor, that effectively kills planktonic and biofilm-associated cells of PsA. In standard tests against 16–18 h-old biofilms, concentrations as low as 16 µg/mL resulted in the extensive disruption and detachment of the matrix. The pre-treatment of biofilms for 30 min with ZnPor at minimum inhibitory concentration (MIC) levels (4 µg/mL) substantially enhanced the ability of tobramycin (Tobra) to kill biofilm-associated cells. We demonstrate the rapid uptake and accumulation of ZnPor in planktonic cells even in dedicated heme-uptake system mutants (ΔPhu, ΔHas, and the double mutant). Furthermore, uptake was unaffected by the ionophore carbonyl cyanide m-chlorophenyl hydrazine (CCCP). Cells pre-exposed to ZnPor took up the cell-impermeant dye SYTOXTM Green in a concentration-dependent manner. The accumulation of ZnPor did not result in cell lysis, nor did the cells develop resistance. Taken together, these properties make ZnPor a promising candidate for treating multi-drug-resistant infections, including persistent, antibiotic-resistant biofilms.

Some topological indices of dendrimers

There are immense applications of graph theory in chemistry and in the study of molecular structures, and after that, it has been increasing exponentially. Molecular graphs have points (vertices) representing atoms and lines (edges) that represent bonds between atoms. In this paper, we study the molecular graph of porphyrin, propyl ether imine, zinc–porphyrin and poly dendrimers and analyzed its topological properties. For this purpose, we have computed topological indices, namely the Albertson index, the sigma index, the Nano-Zagreb index, the first and second hyper [Formula: see text]-indices of porphyrin, propyl ether imine, zinc–porphyrin and poly dendrimers.

Enhanced Electrocatalytic Activity of a Zinc Porphyrin for CO2 Reduction: Cooperative Effects of Triazole Units in the Second Coordination Sphere.

The control of the second coordination sphere in a coordination complex plays an important role in improving catalytic efficiency. Herein, we report a zinc porphyrin complex ZnPor8T with multiple flexible triazole units comprising the second coordination sphere, as an electrocatalyst for the highly selective electrochemical reduction of carbon dioxide (CO2 ) to carbon monoxide (CO). This electrocatalyst converted CO2 to CO with a Faradaic efficiency of 99 % and a current density of -6.2 mA cm-2 at -2.4 V vs. Fc/Fc+ in N,N-dimethylformamide using water as the proton source. Structure-function relationship studies were carried out on ZnPor8T analogs containing different numbers of triazole units and distinct triazole geometries; these unveiled that the triazole units function cooperatively to stabilize the CO2 -catalyst adduct in order to facilitate intramolecular proton transfer. Our findings demonstrate that incorporating triazole units that function in a cooperative manner is a versatile strategy to enhance the activity of electrocatalytic CO2 conversion.

The quest for a better understanding of ethanol coordination to magnesium and zinc porphyrin: A combined experimental and theoretical study

An ethanol coordinated magnesium porphyrin [Mg(TDMPP)(C2H5OH)], (TDMPP = 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)porphyrin), 1 was synthesized and characterized by single crystal X-ray diffraction method along with other standard spectroscopic techniques. This is the first known crystal structure of an alcohol bound magnesium porphyrin of tetraphenylporphyrin derivatives. Crystal structure of the compound shows a weak hydrogen bonding interaction (2.730(4) Å) between OH group of axial ethanol molecule and a peripheral methoxy group of an adjacent porphyrin molecule. This hydrogen bonding results the formation of a weak one-dimensional supramolecular structure. The fluorescence and electrochemical studies have also been performed. To explore the disadvantages of using zinc porphyrins to study chlorophyll type magnesium porphyrins, a comparison of theoretical study using DFT level was performed between compound [Mg(TDMPP)(C2H5OH)], 1 and its zinc counterpart [Zn(TDMPP)(C2H5OH)], 2. Theoretical calculations include optimization of geometry, energy of frontier molecular orbitals (FMOs), electronic transitions and global chemical indices. The global reactivity indices like η, µ and ω derived from theoretical calculations for zinc and magnesium porphyrin supports that magnesium porphyrin is more reactive than the zinc analogue. Furthermore, the Hirshfeld surface analysis was used to quantify the weak intermolecular interactions present in the crystal lattice of compound 1.

Protein-caged zinc porphyrin as a carbonic anhydrase mimic for carbon dioxide capture

Zinc tetraphenylporphyrin (Zn-TPP) solubilized by GroEL protein cage was prepared as a supramolecular mimic of carbonic anhydrase (CA) for CO2 capture. It is shown that the soluble Zn-TPP-GroEL complex can be formed easily by detergent dialysis. The Zn-TPP/GroEL binding ratio was found to increase with their dialysis ratio until reaching the maximum of about 30 porphyrins per protein cage. Moreover, the complex showed hydrase activity that catalyzes the CO2 hydration in HCO3− and H+. It is further seen that the catalytic activity of Zn-TPP-GroEL was about one-half of that of a bovine CA at 25 °C. On the other hand, as the temperature was increased to 60 °C close to an industrial CO2 absorption temperature, the natural enzyme lost function while Zn-TPP-GroEL exhibited better catalytic performance indicative of a higher thermal stability. Finally, we demonstrate that the GroEL-solubilized Zn-TPP is able to accelerate the precipitation of CO2 in the form of CaCO3 and has better long-term performance than the bovine CA. Thus a new type of nano-caged system mimicking natural CAs for potential applications in carbon capture has been established.

Structural perception into the supramolecular self-assembly directed by C[sbnd]H•••π and π•••π interactions of 5,15-di(4′-carboxyphenyl)-10,20-di(pyrenyl) zinc porphyrin linker

Solid state self-assembly of trans-A2B2 metalloporphyrin 5,15-Di(4′-carboxyphenyl)-10,20-Di(pyrenyl) zinc porphyrin linker Zn(H2O)-H2DcpDpyrP directed by CH•••π and π•••π interactions has been investigated. Crystallization of Zn-H2DcpDpyrP in solvent mixture (DMF and methanol) at high temperature followed by slow cooling resulted in the crystals of Zn(H2O)-H2DcpDpyrP (1). Scrutiny of the crystal structure reveals that porphyrin molecules are joined to form a one dimensional polymeric array through self-complimentary OH⋯O interactions between water molecules coordinated to the Zn(II) and 4-carboxyphenyl groups of adjacent molecules. Besides, C–H⋯π and π⋯π stacking interactions played a dominant role to generate extended two dimensional supramolecular sheets and provide stability to the structure. Hirshfeld surface analyses gave an insight into directional as well as strength of the intermolecular interactions. SEM data disclosed a plate shaped morphology which strongly supported the supramolecular self-assembly driven by OH⋯O, CH⋯π and π⋯π interactions.

Terpyridine-containing porphyrin and coordination assembly with fullerene-based pyridine for enhanced electrocatalytic oxygen evolution and photocurrent response

A novel terpyridine-modified porphyrin, ZnP-Pr-tpy, has been synthesized and characterized successfully using elemental analysis, mass spectrometry (MS), nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR) and ultraviolet/visible spectroscopy (UV–Vis). Studies by steady-state fluorescence and UV–visible spectroscopies show that a supramolecular dyad is formed by fullerene-based pyridine (C60-py) and the zinc porphyrin via a coordination bond, with a binding constant K of 1.18 × 105 M−1. The photoexcitation of ZnP-Pr-tpy causes the ground state electrons of the tpy moiety to shift to the ZnP unit via an electron-exchange process following the Dexter energy transfer mechanism. Thus, a donor–acceptor composite film, ZnP-Pr-tpy/C60-py, was fabricated by combining the photosensitizer ZnP-Pr-tpy with C60-py. A comparison of the over-potential at 10 mA/cm2, the Tafel slopes and the photocurrent response under visible light irradiation showed the electrocatalytic oxygen evolution reaction (OER) and the photocurrent response to be clearly improved by the covalent modification of the porphyrin with terpyridine, and further improved by the axial coordination of C60-py to ZnP-Pr-tpy. These improvements are attributed to increased intra- and intermolecular electron transfer, the decrease in the electrochemical impedance resulting from the axial coordination of C60-py to ZnP-Pr-tpy and the electron-exchange in ZnP-Pr-tpy through the Dexter energy transfer mechanism under light excitation.

Visualizing NMR‐shielding effect in fullerene‐ZnPc aggregates: Characteristic patterns of ZnP‐based hosts and encapsulation nature from DFT calculations

AbstractThe formation of supramolecular aggregates incorporating C60 fullerenes can be followed and characterized by nuclear magnetic resonance (NMR) measurements. Here, we unravel the particular patterns provided by zinc‐porphyrin (ZnP)‐bridged dimers, where the aromatic character of each ZnP unit leads to an enhanced shielding region for the closest fullerene atoms, denoting a slight shielding effect for the equatorial atoms. The nature of the stabilization is discussed and compared to a single ZnPC60 aggregate and a ZnP‐dimer (ZnP2C60) model, with a significant contribution from noncovalent ππ interactions, allowing us to address the role of bridging chains. The experimental 13C‐NMR spectrum of C60 in a bridged ZnP dimer shows a single peak owing to the constant tumbling inside the host, which averages the different groups of carbon atoms. The calculations in a static scenario reveal information concerning the local chemical environment underlying the observed shift in relation to isolated C60. We expect that the current approach can be useful to rationalize and predict the origin of the NMR shift upon the formation of host‐guest aggregates involving small and large host species.

Synthesis of Zn(II) porphyrin dyes and revealing an influence of their alkyl substituents on performance of dye-sensitized solar cells

In this study, the series of A3B-type zinc porphyrin dyes have been synthesized for dye-sensitized solar cells (DSSC). All the received zinc-porphyrin complexes bear different alkyl substituents (none, tert-butyl-, methoxy-, hexyloxy-, dodecyloxy-, a pair of hexyloxy-), bulky electron-donating substituent (diphenylamino) in each of three meso-phenyl rings and carboxylic acid as acceptor/anchoring group. The influence of the number and length of alkyl chains on the photophysical properties and DSSCs photovoltaic performance was investigated, as well as quantum-chemical modeling was carried out. Our results reveal that the alkyl chains length and number affect cell performance. We found that DSSC power conversion efficiency increases with an increase in the length and number of alkyl substituents in the porphyrins. A maximum efficiency of 1.29 % was observed in solar cells with dodecyloxy-substituted zinc porphyrin.

Towards More Photostable, Brighter, and Less Phototoxic Chromophores: Synthesis and Properties of Porphyrins Functionalized with Cyclooctatetraene.

Free base and zinc porphyrins functionalized with cyclooctatetraene (COT), a molecule known as a good triplet-state quencher, have been obtained and characterized in detail by structural, spectral, and photophysical techniques. Substitution with COT leads to a dramatic decrease of the intrinsic lifetime of the porphyrin triplet. As a result, photostability in oxygen-free solution increases by two to three orders of magnitude. In non-degassed solutions, improvement of photostability is about tenfold for zinc porphyrins, but the free bases become less photostable. Similar quantum yields of photodegradation in free base and zinc porphyrins containing the COT moiety indicate a common mechanism of photochemical decomposition. The new porphyrins are expected to be much less phototoxic, since the quantum yield of singlet oxygen formation strongly decreases because of the shorter triplet lifetime. The reduction of triplet lifetime should also enhance the brightness and reduce blinking in porphyrin chromophores emitting in single-molecule regime, since the duration of dark OFF states will be shorter.

Bis(4′-tert-butylbiphenyl-4-yl)aniline (BBA)-substituted A3B zinc porphyrin as light harvesting material for conversion of light energy to electricity

Limited synthetic steps via low-cost starting materials are needed to develop large-scale light-active materials for efficient solar cells. Here, novel bis(4[Formula: see text]-tert-butylbiphenyl-4-yl)aniline (BBA) based A3B zinc porphyrin (GB) is synthesized and applied as a light harvesting/electron injection material in dye-sensitized solar cells. The GB sensitizer was characterized by various spectroscopic techniques and the optimized device shows [Formula: see text] of 10.98 ± 0.37 mA/cm2 and power conversion efficiency (PCE) of 3.34 ± 0.26%. In addition, performance is enhanced up to ∼3.9% by the addition of co-adsorbent 3a,7a-dihydroxy-5b-cholic acid (chenodeoxycholic acid, CDCA) to minimize [Formula: see text]-[Formula: see text] staking of the planar porphyrin macrocycles. These results demonstrate that novel broad-absorbing light-active material (GB) could be used for indoor solar panels.

Multipolar Porphyrin-Triazatruxene Arrays for Two-Photon Fluorescence Cell Imaging.

Two-photon excited fluorescent (TPEF) materials are highly desirable for bioimaging applications owing to their unique characteristics of deep-tissue penetration and high spatiotemporal resolution. Herein, by connecting one, two, or three electron-deficient zinc porphyrin units to an electron-rich triazatruxene core via ethynyl π-bridges, conjugated multipolar molecules TAT-(ZnP)n (n=1-3) were developed as TPEF materials for cell imaging. The three new dyes present high fluorescence quantum yields (0.40-0.47) and rationally improved two-photon absorption (TPA) properties. In particular, the peak TPA cross section of TAT-ZnP (436 GM) is significantly larger than that of the ZnP reference (59 GM). The δTPA values of TAT-(ZnP)2 and TAT-(ZnP)3 further increase to 1031 and up to 1496 GM, respectively, indicating the effect of incorporated ZnP units on the TPA properties. The substantial improvement of the TPEF properties is attributed to the formation of π-conjugated quadrapole/octupole molecules and the extension of D-π-A-D systems, which has been rationalized by density function theory (DFT) calculations. Moreover, all of the three new dyes display good biocompatibility and preferential targeting ability toward cytomembrane, thus can be superior candidates for TPEF imaging of living cells. Overall, this work demonstrated a promising strategy for the development of porphyrin-based TPEF materials by the construction and extension of D-π-A-D multipolar array.

Photophysical Properties and Electronic Structure of Zinc(II) Porphyrins Bearing 0-4 meso-Phenyl Substituents: Zinc Porphine to Zinc Tetraphenylporphyrin (ZnTPP).

Six zinc(II) porphyrins bearing 0-4 meso-phenyl substituents have been examined spectroscopically and theoretically. Comparisons with previously examined free base analogues afford a deep understanding of the electronic and photophysical effects of systematic addition of phenyl groups in porphyrins containing a central zinc(II) ion versus two hydrogen atoms. Trends in the wavelengths and relative intensities of the absorption bands are generally consistent with predictions from time-dependent density functional theory calculations and simulations from Gouterman's four-orbital model. These trends derive from a preferential effect of the meso-phenyl groups to raise the energy of the highest occupied molecular orbital. The calculations reveal additional insights, such as a progressive increase in oscillator strength in the violet-red (B-Q) absorption manifold with increasing number of phenyls. Progressive addition of 0-4 phenyl substituents to the zinc porphyrins in O2-free toluene engenders a reduction in the measured lifetime of the lowest singlet excited state (2.5-2.1 ns), an increase in the S1 → S0 fluorescence yield (0.022-0.030), a decrease in the yield of S1 → T1 intersystem crossing (0.93-0.88), and an increase in the yield of S1 → S0 internal conversion (0.048-0.090). The derived rate constants for S1 decay reveal significant differences in the photophysical properties of the zinc chelates versus free base forms. The unexpected finding of a larger rate constant for internal conversion for zinc chelates versus free bases is particularly exemplary. Collectively, the findings afford fundamental insights into the photophysical properties and electronic structure of meso-phenylporphyrins, which are widely used as benchmarks for tetrapyrrole-based architectures in solar energy and life sciences research.