Π-extended Porphyrins Research Articles

Fused Hexabenzocoronene-Porphyrin Conjugates with Tailorable Excited-State Lifetimes.

A new clear-cut strategy for fusing N-heterocyclic and carbon-pure systems is introduced en route to a versatile platform of multi-purpose tetrapyrrolic chromophores. In particular, three novel C-C bond-fused porphyrin-hexabenzocoronene (HBC) conjugates were synthesized under oxidative cyclodehydrogenation conditions, starting from tailor-made nickel porphyrin precursors. The fusion of the individual aromatic systems via 5-membered rings led to highly soluble π-extended porphyrins in excellent yields. The resulting porphyrin-HBC conjugates exhibit absorption cross-sections that are of interdisciplinary interest in the ever-growing field of organic photovoltaics and near-infrared (NIR) dyes. Quantum chemical calculations show that the newly formed 5-membered rings induce biradicaloid character in the porphyrin core, which has a strong impact on excited state lifetimes. This is confirmed by a thorough optoelectronic and time-resolved characterization in order to understand these unique features better. Broadened absorption characteristics go hand-in-hand with short-lived excited states with up to six orders of magnitude faster decay rates.

Synthesis, Structural, Electrochemical, and DFT Studies of Highly Substituted Nonplanar Ni(II) Porphyrins and Their Intensity-Dependent Third-Order Nonlinear Optical Properties.

We designed and successfully synthesized highly substituted electron-deficient nonplanar Ni(II) porphyrins and their derivatives (1-7) in moderate to good yields. These derivatives were comprehensively characterized by various spectroscopic techniques and single-crystal X-ray diffraction (SCXRD) analysis. SCXRD analysis confirmed the structures of compounds 2, 4, and 7, adopting saddle-shape geometry. These nonplanar porphyrins demonstrated significant bathochromic shifts in their absorption spectra compared to parent NiTPP, attributed to the influence of bulky β-substituents and/or peripheral fusion. π-Extended porphyrins 6 and 7 displayed panchromatic absorption spectra extending into the NIR region. Porphyrins 6 and 7 demonstrated a profound anodic shift (∼400 mV) in their first reduction peak potentials compared to precursor NiTPP(NO2)Br6. The experimental absorption spectral pattern matches the simulated absorption spectra obtained from TD-DFT studies. The femtosecond laser intensity-dependent third-order nonlinear optical studies revealed that NiDFP(VCN)2Br6 (6) and NiDFP(VCN)2(PE)6 (7) displayed giant optical nonlinearities compared to the other porphyrins. Among all, NiDFP(VCN)2Br6 (6) possessed the highest two-photon absorption coefficient (β) and cross-section (σTPA) values in the range of 22-33 × 10-10 m/W and 3.77-6.95 × 106 GM, respectively. These findings suggest that the investigated nonplanar π-extended porphyrins are promising candidates for future optoelectronic applications.

(Invited) Molecular Donor-Acceptor Systems Derived from Aromatic Heterocycle-Fused Porphyrins

Photoinduced charge separation (CS) in molecular donor-acceptor (D-A) systems is crucial for achieving efficient solar energy conversion in various applications. Despite significant efforts to develop molecular D-A systems over the past decades, it remains a challenge to bring the lifetime of the charge separation state to ms range, which is much shorter than the CS lifetime (~1 s) in natural photosynthetic systems. In this talk, a donor-acceptor system with long-lived charge-separation state (37.2 μs) will be presented. This donor-acceptor system was derived from π-extended porphyrins fused with aromatic heterocycles. Porphyrins fused with aromatic heterocycles represent one fascinating yet very challenging frontiers in chemistry and materials science.1-4 The Wang group has been engaged in developing concise and versatile synthetic and functionalization methods for π-extended porphyrins. The availability of these methods offers easy access to many π-extended porphyrins with novel functionalities.5-7 In this talk, the synthesis, characterization, and the optical and photophysical properties of π-extended porphyrins fused with 5-, 6, and 7-membered rings including 12H-benzo[f]benzo[4,5]imidazo[2,1-a]isoindole and 1,10-phenanthroline, porphyrins will also be presented. Reference Stepien, E. Gonka, M. Zyla and N. Sprutta, Chem. Rev., 2017, 117, 3479-3716.Narita, X. Y. Wang, X. Feng and K. Mullen, Chem. Soc. Rev., 2015, 44, 6616-6643.P. Lewtak and D. T. Gryko, Chem. Commun., 2012, 48, 10069-10086.K. S. Davis, A. L. Thompson and H. L. Anderson, J. Am. Chem. Soc., 2011, 133, 30-3.Hu, M. B. Thomas, W. A. Webre, A. Moss, R. G. W. Jinadasa, V. N. Nesterov, F. D’Souza and H. Wang, Angew. Chem. Int. Ed., 2020, 45 (132), 20250-20257.Moss, Y. Jang, J. Arvidson, V. N. Nesterov, F. D’Souza and H. Wang, Chem. Sci., 2022, 13, 9880 -9890.Moss, D. E. Nevonen, Y. Hu, V. N. Nesterov, V. Nemykin and H. Wang*, ACS Phys. Chem. Au, 2022, 2, 6, 468-481.

Synthesis and Characterization of Aromatic Heterocycle-Fused Porphyrins

The advances in materials science increasingly demand novel functionalized materials. Porphyrins fused with aromatic moieties represent attractive largely π-extended structures, offering new opportunities in molecular and organic electronics.1-4 In this presentation, new synthetic methods to fuse different type of aromatic rings to the porphyrin periphery will be presented. These new methods have led to the synthesis of novel large π-extended molecular structures incorporating both porphyrins and other aromatic components including acenaphtho[1,2-b]pentacene-, acenaphtho[1,2-b]pentacene quinone, benzodithiophenes and cyclooctatetraenes. Unprecedented electronic and photophysical properties have discovered for these π-extended porphyrins. For example, an unusual trend was observed in the florescence quantum yield upon converting thiophene-attached benzoporphyrin to naphthodithiophene-fused porphyrin. A remarkable light effect was obtained with a acenaphtho[1,2-b]pentacene-fused porphyrin-phthalocyanine heterojunction device, which exhibited high ammonia sensitivity. The characterizations of these π-extended porphyrins including time-resolved emission and transient absorption spectroscopy, cyclic voltammetry, DFT calculations will also be presented. Reference Stepien, E. Gonka, M. Zyla and N. Sprutta, Chem. Rev., 2017, 117, 3479-3716.Narita, X. Y. Wang, X. Feng and K. Mullen, Chem. Soc. Rev., 2015, 44, 6616-6643.P. Lewtak and D. T. Gryko, Chem. Commun., 2012, 48, 10069-10086.K. S. Davis, A. L. Thompson and H. L. Anderson, J. Am. Chem. Soc., 2011, 133, 30-3.Hu, M. B. Thomas, W. A. Webre, A. Moss, R. G. W. Jinadasa, V. N. Nesterov, F. D’Souza and H. Wang, Angew. Chem. Int. Ed., 2020, 45 (132), 20250-20257.Moss, Y. Jang, J. Arvidson, V. N. Nesterov, F. D’Souza and H. Wang, Chem. Sci., 2022, 13, 9880 -9890.Moss, D. E. Nevonen, Y. Hu, V. N. Nesterov, V. Nemykin and H. Wang*, ACS Phys. Chem. Au, 2022, 2, 6, 468-481.Washburn, R. Kaswan, S. Shaikh, A. Moss, F. D’Souza and Hong Wang, J. Phys. Chem. A., 2023,127 (43):9040-9051.Cooper, A. Alsaleh, S. Kumar, W. Rackers, V. N. Nesterov, F. D’Souza, S. A. Vinogradov and H. Wang, Chem. Eur. J., 2023, e202302013.Moss, Y. Jang, H. Wang, F. D’Souza, ChemSusChem, 2023, 16 (8), e202202289.

A Nanographene-Porphyrin Hybrid for Near-Infrared-Ii Phototheranostics.

Photoacoustic imaging (PAI)-guided photothermal therapy (PTT) in the second near-infrared (NIR-II, 1000-1700nm) window has been attracting attention as a promising cancer theranostic platform. Here, it is reported that the π-extended porphyrins fused with one or two nanographene units (NGP-1 and NGP-2) can serve as a new class of NIR-responsive organic agents, displaying absorption extending to ≈1000 and ≈1400nm in the NIR-I and NIR-II windows, respectively. NGP-1 and NGP-2 are dispersed in water through encapsulation into self-assembled nanoparticles (NPs), achieving high photothermal conversion efficiency of 60% and 69%, respectively, under 808 and 1064nm laser irradiation. Moreover, the NIR-II-active NGP-2-NPs demonstrated promising photoacoustic responses, along with high photostability and biocompatibility, enabling PAI and efficient NIR-II PTT of cancer in vivo.

π-Extended Porphyrin-Phthalocyanine Heterojunction Devices Exhibiting High Ammonia Sensitivity with a Remarkable Light Effect.

π-Extended porphyrins represent an attractive class of organic compounds because of their unique photophysical, optoelectronic, and physicochemical properties. Herein, cross-conjugated (Ace-PQ-Ni) and linear-conjugated (AM6) porphyrins are used to build double-layer heterojunction devices by combining them with a lutetium bisphthalocyanine complex (LuPc2). The heterojunction effect at the porphyrin-phthalocyanine interface plays a key role in the charge transport properties. Both devices exhibit exceptionally high ammonia sensitivity at room temperature and under ambient relative humidity, with limit of detection values of 156 and 115 ppb for Ace-PQ-Ni/LuPc2 and AM6/LuPc2 sensors, respectively. Interestingly, the Ace-PQ-Ni/LuPc2 and AM6/LuPc2 sensors display opposite effects upon light illumination. While the former sensors show largely decreased ammonia sensitivity under light illumination, the current variation of the latter under ammonia is remarkably enhanced with a multiplication factor of 13 and a limit of detection (LOD) of 83 ppb. The striking difference in their sensing properties upon light illumination is attributed to their different π-conjugation pathways (cross-conjugation versus linear conjugation).

Electronic and magnetic properties of porphyrin nanoribbons with chelated metals.

Advances in surface-assisted synthesis routes now allow for precise control in the preparation and modification of low-dimensional structures. The choice of molecular precursors plays a fundamental role in these processes since the structural details and properties of the resulting nanostructures directly depend on the molecular block used. From this perspective, units based on porphyrins have proven to be promising candidates for the construction of nanosystems with nontrivial geometry. In particular, efforts have been made to synthesize different arrangements of π-conjugated porphyrins. With this motivation, we use computational simulations to investigate the electronic and magnetic properties of nanoribbons constructed from the concatenation of π-extended porphyrins hosting transition metal atoms. We show that the binding energy of these systems and the specific way the electrons populate the d-shells are strongly influenced by the type of the transition metal. Furthermore, it was observed that most systems with chelated metals (except Ni and Zn) feature magnetic properties. The systems considered in this work have analogs in finite structures recently synthesized in the laboratory so the nanomaterials proposed here have a high potential to be produced in the near future.

Excited-State Charge Transfer in Push-Pull Platinum(II) π-Extended Porphyrins Fused with Pentacenequinone.

Platinum(II) π-extended porphyrins fused with pentacenequinone and dihydropentacene have been successfully synthesized. These porphyrins were investigated using various techniques including absorption, steady-state, and time-resolved phosphorescence spectroscopy and differential pulse voltammetry. UV-vis absorption spectra of pentacenequinone-fused porphyrins (SW-Pt1 and SW-Pt2) showed unusually broad and nontypical absorption patterns. Phosphorescence spectra of SW-Pt1, SW-Pt2, and SW-Pt3 displayed similar emissions in the 704-706 nm region indicating electronic transitions of similar origin; however, the triplet lifetimes were found to be quenched in the case of both SW-Pt1 and SW-Pt2, suggesting the occurrence of excited-state events. Facile reductions were obtained for both the pentacene-quinone-fused monomer (SW-Pt2) and dimer (SW-Pt1) and were identified to be located at the pentacenequinone components. The observed orbital segregations for SW-Pt2 and SW-Pt1 from DFT calculations supported the possibility of charge transfer in these push-pull systems. Interestingly, the established energy level diagram revealed that the charge transfer from the triplet excited Pt porphyrin is thermodynamically an uphill process. Systematic studies involving both femtosecond and nanosecond transient absorption techniques revealed that the singlet excited Pt porphyrins undergo an intermediate charge transfer state prior to populating the triplet state, providing a plausible explanation for phosphorescence quenching. The lifetime of the intermediate charge transfer states was found to be 25.9 and 5.68 ps, respectively, for SW-Pt1 and SW-Pt2.

(Invited) Π-Extended Porphyrins: Fusion of Polycyclic Aromatic Hydrocarbons to Porphyrins

Largely π-extended structures represent one most fascinating yet very challenging frontiers in chemistry and materials science.1, 2 Incorporating both porphyrins and polycyclic aromatic hydrocarbons to obtain largely π-extended multichromophoric systems is especially attractive as the resulted largely π-extended systems are reminiscent of “nanographenes” doped with heteroatoms.3, 4 Due to limited availability of synthetic methods, only the simplest symmetrical π-extended porphyrins remain largely unexplored. The Wang group has been engaged in developing concise and versatile synthetic and functionalization methods for π-extended porphyrins. The availability of these methods offers easy access to many p-extended porphyrins with novel functionalities.5-7 In this talk, the synthesis, characterization, and the optical and photophysical properties of π-extended porphyrins fused with 5- and 6-membered rings including pentacene-, pentaquinone-, acenaphtho[1,2-b]pentacene- and 12H-benzo[f]benzo[4,5]imidazo[2,1-a]isoindole-fused porphyrins will be presented. Figure 1

Achieving simultaneous sensing of oxygen and temperature with metalloporphyrins featuring efficient thermally activated delayed fluorescence and phosphorescence

Temperature is an essential parameter for reliable assessment of oxygen concentration by optical sensors. This can be done by a conventional sensor such as a resistance thermometer or by adding an optical temperature probe to the sensing material. A sensor that relies on a single emitter capable of simultaneous sensing of oxygen and temperature would be highly advantageous. Unfortunately, such materials are extremely rare and moreover poorly suitable for measurement at ambient temperatures and physiological conditions. To cover this gap, we systematically investigated 15 Pd(II) and 6 Pt(II) complexes of π-extended porphyrins that simultaneously emit thermally activated delayed fluorescence (TADF) and phosphorescence. The class of quinone-extended benzoporphyrins was found to feature especially high ratios of TADF to phosphorescence (1.4–2.7 and 0.10–0.21, for Pd(II) and Pt(II) complexes, respectively, at 25 °C) which represents approximately a sixteen-fold improvement compared to the benchmark octasulfone-substituted porphyrins. Interconversion of phosphorescence into TADF with increasing temperature enables ratiometric measurement of this parameter in the range from 0 to about 65 °C whereas the oxygen concentration is accessed through the decay time of either TADF or phosphorescence. Simultaneous sensing of both temperature and oxygen is demonstrated for a naphthoquinone-extended Pt(II) benzoporphyrin embedded in polystyrene that shows dual emission with maxima at 677 and 789 nm. The sensor is characterized for temperatures from 5° to 55 °C and oxygen partial pressure from 0 to 202 hPa, corresponding to the conditions found in the majority of applications. As an application example temperature compensated imaging of oxygen distribution is demonstrated.

Cascade Amination and Aza-6π-Annulation-Aromatization Strategy for the Synthesis of β-Pyrimidine-Fused Porphyrins.

Novel nickel(II) and copper(II) complexes of 2-(N,N-dimethylformamidine)-3-formyl-5,10,15,20-tetraarylporphyrins have been synthesized for the first time from 2-aminoporphyrins under Vilsmeier-Haack conditions. These porphyrins are utilized as new building blocks to construct diverse β-pyrimidine-fused 5,10,15,20-tetraarylporphyrins in good yields via a cascade ammonia-mediated condensation and intramolecular aza-6π-annulation/aromatization in 1,2-dichloroethane at 80 °C. Furthermore, copper(II) β-pyrimidine-fused porphyrins underwent demetallation in the presence of conc. H2SO4 to afford free-base porphyrins, which on zinc insertion using Zn(OAc)2 in CHCl3-MeOH provided zinc(II) β-pyrimidine-fused porphyrins in appreciable yields. Notably, these newly synthesized π-extended porphyrins displayed a modest bathochromic shift in their electronic absorption and emission spectra as compared to the traditional meso-tetraarylporphyrins. However, the protonated porphyrins (2a) and (3g) displayed a significant red-shifted absorption.

Near-Infrared Photodynamic Therapy with π-Extended Porphyrins

Near-Infrared Photodynamic Therapy with π-Extended Porphyrins

Antibacterial Photodynamic Therapy in the Near-Infrared Region with a Targeting Antimicrobial Peptide Connected to a π-Extended Porphyrin.

The increase of antimicrobial resistance to conventional antibiotics is worldwide a major health problem that requires the development of new bactericidal strategies. Antimicrobial photodynamic therapy (a-PDT) that generates reactive oxygen species acting on multiple cellular targets is unlikely to induce bacterial resistance. This localized treatment requires, for safe and efficient treatment of nonsuperficial infections, a targeting photosensitizer excited in the near IR. To this end, a new conjugate consisting of an antimicrobial peptide linked to a π-extended porphyrin photosensitizer was designed for a-PDT. Upon irradiation at 720 nm, the conjugate has shown at micromolar concentration strong bactericidal action on both Gram-positive and Gram-negative bacteria. Moreover, this conjugate allows one to reach a low minimum bactericidal concentration with near IR excitation without inducing toxicity to skin cells.

On-Surface Synthesis of Fused Anthracenyl Porphyrin Derivatives

For the last fifteen years, on-surface synthesis became an extremely popular and powerful method to fabricate nanostructures which otherwise would not have been accessible by conventional wet organic syntheses. The syntheses, realized in the chamber of high vacuum scanning tunneling microscope (STM), permitted the fabrication and the characterization of atomically defined nanostructures such as polycyclic aromatic hydrocarbons (PAH), graphene nanoribbons or 2D covalent networks.1 Among the organic molecules studied by STM, porphyrins are of particular importance because of their electronic and optical properties. Initial studies were mainly devoted to the supramolecular organization of porphyrins and porphyrin derivatives on surface and it is only in 2004 that noble metal surfaces were used as catalytic surface to perform reactions on the porphyrin cores.2 Since then, examples of open-shell porphyrin derivatives3 and conjugated oligomers4 were reported.While the synthesis of fused bis- and tetra-4,5-bis-(2,4,6-trimethylphenoxy)anthracen-9-yl porphyrins containing Ni(II) was reported by Anderson about 10 years ago,5 the formation π-extended porphyrin bearing unsubstituted anthracenyl moieties were never achieved. The formation of such compounds became possible by on-surface synthesis. Herein, we report on the synthesis of fused bis- and tetra-anthracenylporphyrin derivatives via the cyclodehydrogenation the parent meso-substituted molecules on a catalytic Au(111) surface.6 Depending on the annealing temperature, anthracenylporphyrins with the four anthracene fully linked to the porphyrin core or over-oxidized porphyrin in which the anthracene are connected two by two in 2-2’ position were observed by STM (Figure 1). Figure 1. STM images of the fused tetra-anthracenylporphyrins and related porphyrin structures References Clair, S.; de Oteyza, D. G. Chem. Rev. 2019, 119, 4717-4776.Fox, S.; Boyle, R. W. Chem. Commun. 2004, 1322-1323.a) Sun, Q.; Mateo, L. M.; Robles, R.; Ruffieux, P.; Lorente, N.; Bottari, G.; Torres, T.; Fasel, R. J. Am. Chem. Soc. 2020, 142, 18109-18117; b) Zhao, Y.; Jiang, K.; Li, C.; Liu, Y.; Xu, C.; Zheng, W.; Guan, D.; Li, Y.; Zheng, H.; Liu, C.; Luo, W.; Jia, J.; Zhuang, X.; Wang, S. J. Am. Chem. Soc. 2020, 142, 18532-18540.a) Mateo, L. M.; Sun, Q.; Liu, S.-X.; Bergkamp, J. J.; Eimre, K.; Pignedoli, C. A.; Ruffieux, P.; Decurtins, S.; Bottari, G.; Fasel, R.; Torres, T. Angew. Chem., Int. Ed. 2020, 59, 1334-1339; b) Mateo, L. M.; Sun, Q.; Eimre, K.; Pignedoli, C. A.; Torres, T.; Fasel, R.; Bottari, G. Chem. Sci. 2021, 12, 247-252.a) Davis, N. K. S.; Thompson, A. L.; Anderson, H. L. Org. Lett. 2010, 12, 2124-2127; b) Davis, N. K. S.; Thompson, A. L.; Anderson, H. L. J. Am. Chem. Soc. 2011, 133, 30-31.Baljozović, M. et al., in preparation Figure 1

Porphyrindiene-Based Tandem Diels–Alder Reaction for Preparing Low-Symmetry π-Extended Porphyrins with Push–Pull Skeletons

Tandem Diels-Alder reactions of masked porphyrindienes (i.e., sulfolenoporphyrins) with benzoquinones and stilbenes, followed by aromatization, have been developed to load porphyrin with mixed annulation units (i.e., terphenyl and naphthoquinone), furnishing the low-symmetry π-extended porphyrins (DxAy) with push-pull skeletons. All low-symmetrical chromophores display panchromatic absorption spectra, which look like a spectral combination of symmetrical congeners (D4/A4) in a certain ratio. Among them, tD2A2 with trans-arrangement of push/pull units possesses the largest maximum centered at 766 nm with the onset around 900 nm. The fusion of the electron-deficient naphthoquinone moiety on the porphyrin core results in the approximately quantitative regulation of the Eox1 and HOMOs (i.e., 0.10-0.13 V increase for the Eox1 and 0.14-0.16 eV decrease for the HOMOs per naphthoquinone unit). In brief, this work provides a new way to construct low-symmetry π-extended porphyrins with tunable properties resorting to the ratios and locations of the annulated push-pull units.

Unsymmetrically β-Functionalized π-Extended Porphyrins: Synthesis, Spectral, Electrochemical Redox Properties, and Their Utilization as Efficient Two-Photon Absorbers.

Two new series of unsymmetrically β-functionalized porphyrins, MTPP(NO2)MA (1M), (MA = methyl acrylate) and MTPP(NO2)MB (2M) (MB = mono-benzo) (where M = 2H, Co(II), Ni(II), Cu(II) and Zn(II)), were synthesized and characterized by various spectroscopic techniques. The saddle shape conformation of ZnTPP(NO2)MAPy and ZnTPP(NO2)MB was confirmed by single-crystal X-ray analysis. Density functional theory (DFT) calculation revealed that NiTPP(NO2)MB has a severe nonplanar geometry possessing a high magnitude of ΔCβ = ±0.727 Å and Δ24 = ±0.422 Å values among all other porphyrins. Synthesized β-substituted porphyrins exhibited red-shifted B- and Q-bands corresponding to their parent molecule due to the electron-withdrawing peripheral substituents. Notable redshift (Δλmax = 50-60 nm) in electronic spectral features and with weak-intensity emission spectral features were observed for the free-base porphyrins and Zn(II) complexes compared to H2TPP and ZnTPP, respectively. The first-ring reduction potential of MTPP(NO2)MA (1M) exhibited 0.21-0.5 V anodic shift, whereas 0.18-0.23 V anodic shift was observed in the first-ring oxidation potential compared to the corresponding MTPPs due to the presence of electron-withdrawing β-substituents at the periphery of the macrocycle. Interestingly, NiTPP(NO2)MA (1Ni) has shown an additional NiII/NiIII oxidation potential observed at 2.05 V along with two ring-centered oxidations. The first-ring reduction and oxidation potentials of MTPP(NO2)MB (2M) have shown 0.39-0.46 and 0.19-0.27 V anodic shifts with respect to their corresponding MTPPs. The nonlinear optical (NLO) properties of all of the porphyrins were investigated, and the extracted nonlinear optical parameters revealed intense reverse-saturable absorption (RSA) behavior and the self-focusing behavior with positive nonlinear refractive index in the range of (0.19-1.75) × 10-17 m2/W. Zn(II) complexes exhibited the highest two-photon absorption coefficient (β) and cross section (σTPA) of ∼95 × 10-12 m/W and 19.66 × 104 GM, respectively, among all of the metal complexes.

Copper naphthoporphyrin showing enhanced water-solubility by nano-encapsulation and efficient photoacoustic response

ABSTRACT Here, we report the facile synthesis of Cu(II) tetraaryl-tetranaphtoporphyrin CuTNP showing an extremely sharp, intense Q band above 700 nm via retro-Diels-Alder approach. The highly saddled structure of CuTNP was confirmed using X-ray single-crystal diffraction. The optical and magnetic properties of CuTNP, as well as its excellent reversible redox behaviours, were thoroughly examined both experimentally and theoretically. The water-soluble nanocomposites encapsulating CuTNP by bent amphiphilic molecules were successfully developed, which kept the intense Q band of CuTNP in water. The strong photoacoustic response of CuTNP was detected, suggesting its potential as a photoacoustic imaging agent. This work provides metal-coordinated linearly π-extended porphyrins as potential functional materials for future biomedical applications.

Thermally Induced Synthesis of Anthracene-, Pyrene- and Naphthalene-Fused Porphyrins.

The synthesis of π‐extended porphyrins containing anthracenyl moieties still represents an important challenge. Here, we report on the synthesis of a series of unsubstituted naphthyl‐, pyrenyl‐ and anthracenyl‐fused zinc porphyrin derivatives. To this aim, meso‐substitued porphyrins are synthesized and the fusion of the PAHs (Polycyclic Aromatic Hydrocarbon) on the β‐positions are performed through thermally induced dehydro‐aromatization. The fused zinc‐porphyrin derivatives are fully characterized and their optical absorption and photoluminescence properties are reported. We also demonstrate that zinc can be removed from the porphyrin core, giving rise to pure C, H, N materials. This work constitutes the first step towards the synthesis of the fully‐fused tetra‐anthracenylporphyrin.

Electrosynthesis of π-Extended Porphyrins Via Reductive Decyanation

The development of new electrochemically driven synthetic routes to obtain π-extended porphyrins, or new synthetic porphyrins in general, is highly desirable since electrosynthesis is often able to afford a clean conversion of reactants to products without a great deal of contamination. At the same time, electrosynthesis, when combined with classical electrochemical measurements, can often provide unique insights into the mechanism and intermediates involved in formation of the desired product. This is explored in the current work where a novel electrosynthetic method for generation of π-extended porphyrins and the corresponding reductive decyanation mechanism is described. The heterogenous anion induced electrosynthetic method is also compared to a homogenous chemical synthesis method to obtain the same products, using anion-induced electron transfer (AIET). The starting porphyrins are β,meso-fused malononitrile derivatives are represented as MTPP(MN)2 and the π-extended, di-fused products as MTPP(VCN)2, where TPP = the dianion of tetraphenylporphyrin, MN = malononitrile, VCN = vinyl cyanide and M = H2, NiII, CuII and ZnII. Structures of these porphyrins are shown in Chart 1. The easily synthesized π-extended porphyrins with two fused cyanobenzene (benzonitrile) rings are characterized by three facile and reversible one-electron ring-centered reductions in THF containing 0.1 M TBAP. There is also a fourth irreversible reduction at the edge of the solvent. Figure 1

Synthesis, Spectral and Electrochemical Studies of β-Trisubstituted Porphyrins and Monobenzoporphyrins

Meso-Tetraarylporphyrins having electron-withdrawing substituents viz. nitro, formyl, acyl, or bromo groups is the key precursor to expand the chemistry of β-functionalized porphyrins.1 These β-functionalized porphyrins have been utilized in nonlinear optics, anion sensing, gas storage, photodynamic therapy (PDT), and dye-sensitized solar cells (DSSC).2 Modulating the degree of π-conjugation and introducing suitable donor-acceptor substituents at β-positions result red-shifted electronic spectral features, low HOMO-LUMO gap and high ground state dipole moment which are essentials for enhanced nonlinear optical behavior. Benzoporphyrin derivatives are currently under investigation as photosensitizers for PDT.3 Herein, we synthesized unsymmetrically functionalized trisubstituted porphyrins and monobenzoporphyrins in one step and characterized by various spectroscopic techniques viz. UV-vis, fluorescence, NMR, MALDI-TOF mass spectrometry and electrochemical studies.The synthesized trisubstituted porphyrins and monobenzoporphyrins were significantly red-shifted as compared to their precursor porphyrins. Further, these porphyrins exhibited a large anodic shift in reduction and cathodic shift in oxidation potentials due to extended π-conjugation and electron-withdrawing β-substituents. In this presentation, we will present the facile synthesis, photophysical and intriguing electrochemical redox properties of π-extended porphyrins. Figure 1. Molecular structures, absorption spectral profile and cyclic voltammograms of synthesized porphyrins.