Porphyrin Tapes Research Articles

A Doubly meso-α Linked N-Confused Porphyrin Tape Silver(III) Complex Comprising an Antiaromatic Pyrrolo[2,3-f]indole Segment.

The free base form of doubly meso-α linked N-confused porphyrin (NCP) tape 3 was successfully synthesized via Ir(I) mediated intramolecular coupling. The following silver complexation afforded the Ag(III) complex of doubly meso-α linked NCP tape 4. While 3 exhibited 38π aromatic characters, 4 exhibited not only 18π aromatic NCP-type characteristics but also a decent antiaromatic contribution of 12π pyrrolo[2,3-f]indole segment, as probed by NMR spectra, absorption spectra, and DFT calculations.

Modulating the Shape of Short Metal-Mediated Heteroleptic Tapes of Porphyrins.

In view of developing artificial light-responsive complex systems, the preparation of discrete and robust heteroleptic assemblies of different chromophores in precisely defined positions is of great value since they would allow to investigate directional processes unavailable in symmetrical architectures. Here we describe the preparation, through a modular stepwise approach, and characterization of four novel and robust metal-mediated heteroleptic 4+3 porphyrin tapes, labeled D4 -T4 -D4 , D3 -T4 -D3 , D4 -T3 -D4 , and D3 -T3 -D3 , where a central meso-tetrapyridylporphyrin (either 3'-TPyP=T3 or 4'-TPyP=T4 ) is connected to two equal cis-dipyridylporphyrins (either 3'cisDPyMP=D3 or 4'cisDPyMP=D4 ) through four {t,c,c-RuCl2 (CO)2 } fragments. Whereas D4 -T4 -D4 is flat, the tapes containing at least one 3'PyP, i. e. D3 -T4 -D3 , D4 -T3 -D4 , and D3 -T3 -D3 , have unprecedented - and well defined - 3D geometries, and each exists in solution as a pair of stereoisomers in slow conformational equilibrium. The X-ray molecular structures of two such conformers, the C-shaped (D3 -T4 -D3 )C and the z-shaped (D4 -T3 -D4 )z , were determined and are fully consistent with the solution NMR findings.

A Quadruply Bridged Non‐Offset Face‐to‐Face Porphyrin Dimer and Cross‐Shaped Pentameric Porphyrin Tapes Based on 2,7,12,17‐Tetrakis(pinacolatoboryl) NiII Porphyrin

Abstract2,7,12,17‐Tetrakis(pinacolatoboryl) NiII porphyrin 5 Ni was synthesized in 75 % yield by Ir‐catalyzed borylation of porphine followed by NiII metalation and has been demonstrated to be a useful synthon, giving 2,7,12,17‐tetraaryated NiII porphyrins 6 a–d, peripherally octaarylated NiII porphyrins 8 a–d, quadruply bridged face‐to‐face non‐offset NiII‐porphyrin dimer 12, and cross‐shaped β‐meso singly linked porphyrin pentamers and nonamers. Oxidation of cross‐shaped β‐meso singly linked porphyrin pentamers 14 Ni and 14 Zn gave fused pentameric tapes 15 Ni and 15 Zn. The structures of 12, 14 Zn, and 15 Ni have been revealed by X‐ray diffraction analysis. Optical separation of 12 has been accomplished, showing a bisignate coupling pattern for exciton‐coupled blue‐shifted Soret band. Pentameric porphyrin tape 15 Zn exhibits a red‐shifted absorption band at 1156 nm and seven reversible redox waves.

A Quadruply Bridged Non-Offset Face-to-Face Porphyrin Dimer and Cross-Shaped Pentameric Porphyrin Tapes Based on 2,7,12,17-Tetrakis(pinacolatoboryl) NiII Porphyrin.

2,7,12,17-Tetrakis(pinacolatoboryl) NiII porphyrin 5 Ni was synthesized in 75 % yield by Ir-catalyzed borylation of porphine followed by NiII metalation and has been demonstrated to be a useful synthon, giving 2,7,12,17-tetraaryated NiII porphyrins 6 a-d, peripherally octaarylated NiII porphyrins 8 a-d, quadruply bridged face-to-face non-offset NiII -porphyrin dimer 12, and cross-shaped β-meso singly linked porphyrin pentamers and nonamers. Oxidation of cross-shaped β-meso singly linked porphyrin pentamers 14 Ni and 14 Zn gave fused pentameric tapes 15 Ni and 15 Zn. The structures of 12, 14 Zn, and 15 Ni have been revealed by X-ray diffraction analysis. Optical separation of 12 has been accomplished, showing a bisignate coupling pattern for exciton-coupled blue-shifted Soret band. Pentameric porphyrin tape 15 Zn exhibits a red-shifted absorption band at 1156 nm and seven reversible redox waves.

Theoretical study on porphyrin arch-tapes of carbonyl-inserted seven-membered rings with high nonlinear optical properties.

Porphyrin tapes have attracted extensive attention because their fully conjugated π-networks act as nonlinear optical (NLO) materials. A family of Ni(II) and Zn(II) porphyrin arch-tapes that are connected by varying bridge (B) ligands (meso-meso β-β doubly linked dimer 1, meso-meso β-β β-β triply linked dimer 3, methylene-inserted dimer 2 and trimer 5, carbonyl-inserted dimer 4, trimer 6, and Zn(II) trimer 7) have been synthesized by a density functional theory (DFT) method. The results show that carbonyl-inserted arch-tapes significantly enhance second hyperpolarizability (γ), indicating that the remarkably contorted structure incorporated seven-membered ring(s) directly affect their NLO properties of our focus. Moreover, the electronic absorption spectra calculated for all studied complexes with time-dependent DFT theory (TDDFT) predict that carbonyl-inserted complex 4 contributes to a red-shift of the Q-band (160 nm) for the meso-meso β-β doubly linked complex 1. The third-order NLO responses and the electron transition properties strongly depend on the nature of the bridge (B) ligand, which means that an active involvement of the carbonyl group presents an advantage for its application in NLO materials.

Heterometallic Porphyrin Conjugated Polymer Thin Films—A Gas‐Phase Approach for the Engineering of New Fused Porphyrin Systems

AbstractFor the first time, the simultaneous synthesis and deposition of heterometallic porphyrin conjugated polymer thin films from a simple and scalable gas‐phase approach are reported. The oxidative chemical vapor deposition (oCVD) reaction of 5,15‐(diaryl) porphyrins chelated with different metal cations (M = Co(II), Ni(II), Zn(II), Cu(II), Pd(II)) readily yields the formation of new hetero‐metalated fused porphyrin tapes, such as evidenced by in‐depth high‐resolution mass spectrometry studies. The impact of the coreactants on the regioselectivity of the intermolecular dehydrogenative coupling reaction and the formation of double or triple bonds between the porphyrin units is demonstrated. The oCVD reaction of multiple porphyrins brings the possibility to easily engineer the chemical features and the electronic and optoelectronic properties of these highly conjugated porphyrin polymers. Particularly, it is demonstrated that porphyrin conjugated polymers having different chelated metal cations can achieve higher electrical conductivities and promote narrower bandgaps. The gas‐phase approach presented herein overcomes the main limitations of the conventional solution‐based approaches and opens the path to the engineering of a novel class donor–acceptor heterometallic polymers with high interest in several fields including multimetallic electrocatalysis, photocatalysis, sensing, and nonlinear optics applications.

A Fully Conjugated Porphyrin-[36]Octaphyrin-Porphyrin Hybrid Tape Exhibiting Möbius Aromaticity.

Directly meso-meso linked porphyrin-tetrabromo[36]octaphyrin-porphyrin hybrid trimer 10 was successfully synthesized via acid-catalyzed condensation reaction and subsequent oxidation. ZnII -metalation of 10 induced transannular meso-meso bond formation to give Möbius aromatic bis-ZnII octaphyrin 11, which was oxidized by DDQ/Sc(OTf)3 to provide fully conjugated porphyrin-[36]octaphyrin-porphyrin hybrid tape 12 as the first example of porphyrin tape exhibiting Möbius aromaticity. Hybrid tape 12 displays significantly red-shifted absorption and small electrochemical HOMO-LUMO gap, indicating the effective conjugation through the whole chromophores.

Accurate Prediction of the Excited States in the Fully Conjugated Porphyrin Tapes across the Full Spectral Range: A Story of the Interplay between π-π* and Intramolecular Charge-Transfer Transitions in Soft Chromophores.

The ability of density functional theory (DFT) and time-dependent DFT (TDDFT) methods for the accurate prediction of the energies and oscillator strengths of the excited states in a series of fully conjugated meso-meso β-β β-β triple-linked porphyrin oligomers (porphyrin tapes 2-12) was probed in the gas phase and solution using several exchange-correlation functionals. It was demonstrated that the use of the hybrid B3LYP functional provides a good compromise for the accurate prediction of the localized π-π* and intramolecular charge-transfer transitions, thus allowing confident interpretation of the UV-vis-NIR spectra of porphyrin oligomers. The TDDFT-based sum-over-state (SOS) calculations for the porphyrin tape dimer 2 and trimer 3 as well as parent monomer 1 correctly predicted the signs and shapes of the magnetic circular dichroism (MCD) signals in the low-energy region of the spectra.

A structural parameter to link molecular geometry to macroscopic orientation in discotic liquid crystals: study of metalloporphyrin tapes

Novel liquid crystalline (LC) molecules were prepared from a dimeric porphyrin tape. A series of metal complexes (1Zn, 1Pd, 1Cu, and 1Ni) and the free-base form (12H) of the porphyrin tape formed a columnar LC phase. Although only the central metal ions were different among these compounds, 1Ni, 12H, and 1Cu aligned homeotropically in a sandwiched glass cell, while 1Zn and 1Pd exhibited a random orientation at a macroscopic scale. The strength of the π-π interactions, tunable by the distortion of the porphyrin cores through metallation, is a key factor for the observed macroscopic orientation difference.

Molecular Engineering of Porphyrin‐Tapes/Phthalocyanine Heterojunctions for a Highly Sensitive Ammonia Sensor

AbstractModulating the interfacial charge alignments by molecular engineering in an organic heterojunction device is a smart strategy to improve its conductivity, which can be exploited in high‐performance gas‐sensor development. Herein, the fabrication of new organic heterojunction devices based on porphyrin tapes and phthalocyanines and their potentiality in ammonia sensing at different relative humidity (rh) are investigated. The devices are built using dry approach relying on oxidative chemical vapor deposition for simultaneous synthesis, doping, and deposition of the porphyrin tape layer and physical vapor deposition of phthalocyanine layer. The association of the porphyrin tapes with copper phthalocyanine (CuPc) or its perfluorinated analogue (Cu(F16Pc)) in a bilayer device configuration reveals a nonlinear current–voltage characteristic, assigned to the formation of organic heterojunction at the bilayer interface. Cu(F16Pc)‐based devices reveal higher response, faster sorption kinetics, stable baseline, and less interference from rh fluctuations toward ammonia than CuPc‐based devices, which are attributed to more conducting interface in the former. Moreover, depending on the porphyrin tape associated, Cu(F16Pc)‐based devices exhibit sensitivity values 6.7 or 0.4% ppm−1 and detection limit of 1 ppm or 228 ppb allowing to obtain among the best NH3 sensors reported.

Global Aromaticity in a Partially Fused 8-Porphyrin Nanoring.

Template-directed synthesis has been used to prepare a fully π-conjugated cyclic porphyrin octamer, composed of both β,meso,β-edge-fused porphyrin tape units and butadiyne-linked porphyrins. The UV-vis-NIR spectra of this partially fused nanoring show that π-conjugation extends around the whole macrocycle, and that it has a smaller HOMO-LUMO gap than its all-butadiyne-linked analogue, as predicted by TD-DFT calculations. The 1H NMR shifts of the bound templates confirm the disrupted aromaticity of the edge-fused porphyrins in the neutral nanoring. NMR oxidation titrations reveal the presence of a global paratropic ring current in its 4+ and 8+ oxidation states and of a global diatropic ring current in the 6+ state of the partially fused ring. The paratropic ring current in the 4+ oxidation state is about four times stronger than that in the all-butadiyne-linked cyclic octamer complex, whereas the diatropic current in the 6+ state is about 40% weaker. Two isomeric K-shaped tetrapyridyl templates with trifluoromethyl substituents at different positions were used to probe the distribution of the ring current in the 4+, 6+, and 8+ oxidation states by 19F NMR, demonstrating that the ring currents are global and homogeneous.

Molecular flattening effect to enhance the conductivity of fused porphyrin tape thin films.

The straightforward synthesis of directly fused porphyrins (porphyrin tapes) from 5,15-diphenyl porphyrinato nickel(ii) complexes with different substituents on the phenyl rings is achieved while processing from the gas phase. The porphyrin tapes, exhibiting NIR absorption, are readily obtained in thin film form. The gas phase approach cuts the need for solubilizing groups allowing for the first time the study of their conductivity according to the substituent. 2-Point probe and conductivity AFM measurements evidence that reducing the size of the meso substituents, phenyl < mesityl < di(3,5-tert-butyl)phenyl < di(2,6-dodecyloxy)phenyl, improves the thin film conductivity by several orders of magnitude. Density functional theory and gel permeation chromatography, correlate this improvement to changes in the intermolecular distances and molecular geometry. Furthermore, the oCVD of porphyrins with free ortho-phenyl positions causes intramolecular dehydrogenative side reactions inducing a complete planarization of the molecule. This molecular flattening drastically affects the π–π stacking between the porphyrins further enhancing the electronic properties of the films.

On-Surface Synthesis of Chiral π-Conjugate Porphyrin Tapes by Substrate-Regulated Dehydrogenative Coupling

On-surface enantioselective covalent coupling of nonfunctionalized porphyrins is demonstrated without utilizing chirality transfer from a self-assembled enantiopure precursor structure. We achieved...

Gas Phase Synthesis and Deposition of Directly Fused Porphyrin Tapes: Reaction Mechanism and Central Metal Ion Effect.

The formation of directly fused porphyrin tapes attracted the interest of the scientific community because of their electronic and optical properties such as extremely low bandgap, NIR and two photon absorption. The synthesis of these compounds is tedious because of their low solubility and require the introduction of solubilizing substituents adding further synthetic efforts.[1] Moreover, these materials are hard to process and integrate into device while the solubilizing substituents hinder the π­-π interactions affecting the properties of the resulting materials.[1],[2] These drawbacks were circumvented with the oxidative Chemical Vapour Deposition (oCVD) of phenyl meso-substituted porphyrins, which allowed to achieve in a single step the synthesis, deposition and doping of polymeric fused porphyrins tapes thin films from commercially available chemicals.[2] Our approach allows the deposition of patterned films and is compatible with sensitive substrates such as paper or polymers (Figure 1a). Using Ni(II) 5,15–(diphenyl) porphyrin (NiDPP), 5,10,15–(triphenyl) porphyrin (NiP3P) and 5,10,15,20–(tetraphenyl) porphyrin (NiTPP), we elucidate the reaction active sites, the side reactions (Figure 1b) and the differences to solution based approaches via high resolution mass spectrometry, UV-Vis-NIR spectroscopy, electron paramagnetic resonance (EPR) and Density Functional Theory (DFT). We also investigate the effect of the central metal ion on the direct fusion reaction of Fe(III)Cl, Co(II), Ni(II), Cu(II), Pd(II), H2 and Zn(II), 5,15–(diphenyl) porphyrins in oCVD. Furthermore, the electrical, electronic and morphological properties of the prepared thin films were thoroughly investigated by means of X-ray Photoelectron Spectroscopy (XPS), Helium Ion Microscopy (HIM) and Conductive Atomic Force Microscopy (C-AFM). [1] T. Tanaka, A. Osuka – Conjugated porphyrin arrays: synthesis, properties and applications for functional materials – Chem Soc Rev. 2015, 44, 943. [2] G. Bengasi, K. Baba, G. Frache, P. Gratia, K. Heinze, N. D. Boscher – Conductive Fused Porphyrin Tapes on Sensitive Substrates by a Chemical Vapor Deposition Approach – Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201814034. Figure 1) a) The chemical vapour deposition reaction of NiDPP and FeCl3 yields a homogeneous and conductive coating also on sensitive and bendable substrates which evidences the suitability for modern optoelectronic devices. b) Reaction schemes for the CVD reaction of NiDPP and FeCl3 and side reactions observed during the deposition (chlorination, cyclization of the phenyl ring). Figure 1

Conductive Directly Fused Metalloporphyrin Coatings By Chemical Vapour Deposition – from Singly to Triply Fused

Porphyrins, whose central structure is composed of four pyrrole units joined by four methine bridges, have been selected by nature to fulfil the two main catalytic phenomena allowing life, i.e. photosynthesis and respiration. Their remarkable functional properties led to the development of numerous porphyrinic compounds for various technological applications, including catalysis and photocatalysis. Porphyrin’s properties can be adjusted by tuning the central metal ion or the pendant groups located at the meso or beta positions. The properties of porphyrin-based devices are also greatly dependent on their integration mode since porphyrins may be directly used dissolved in a liquid medium, covalently grafted onto a surface, embedded in a matrix or polymerised. Conjugated porphyrin polymers,[1] including directly fused porphyrins,[2] display a cooperative effect promoted by conjugated covalent links between porphyrins that yields superior catalytic performances.[1,2] However, the two main synthetic routes towards conjugated poly(porphyrins), (i) oxidative polymerization using a suitable oxidant or (ii) electrodeposition, are a major drawback to their integration into devices. Indeed, the weak solubility of porphyrin monomers, oligomers and polymers requires the introduction of bulky pendant groups to form conjugated poly(porphyrins) in which the tetrapyrrole moieties responsible for the targeted properties end-up diluted. In this work, we report a straightforward chemical vapour deposition approach for the simultaneous synthesis and deposition of conjugated poly(porphyrin) coatings from a simple and commercially available metalloporphyrin, i.e. nickel(II) 5,15-(diphenyl)porphyrin (NiDPP).[3] Our approach relies on the vapour-phase delivery of NiDPP and an oxidant towards a substrate on which they adsorb and react to form conjugated polymer coatings. The direct fusion of NiDPP is notably demonstrated by ultraviolet-visible-near infrared spectrophotometry (UV-Vis-NIR) and high-resolution mass spectrometry (HRMS). Among the investigated oxidants, FeCl3 appears as the candidate of choice for the oxidative fusion of NiDPP in CVD and control of the reactants ratio alternatively allowed the formation of singly-fused P(NiDPP) coatings or multiply-fused (doubly and triply) P(NiDPP) coatings such as evidenced by HRMS. UV-Vis-NIR and conductivity atomic force microscopy (C-AFM) highlight the strong dependence of the optical absorption and electrical conductivity of the fused NiDPP films on the degree of conjugation, opening up the possibility to tune the optoelectronic properties of the P(NiDPP) coatings. Noticeably, the multiply fused P(NiDPP) tapes in thin film form exhibit an electrical conductivity up to 7·10–1 S·cm–1 coupled an absorption deep in the NIR. Our gas-phase reaction approach considerably simplified the integration of fused metalloporphyrins into devices.[3] Following to the very recent report of the superior catalytic activity of fused copper porphyrin dimers,[2] the oCVD reaction of metalloporphyrins will allow the straightforward preparation of potent heterogeneous single‐site catalysts. [1] J. Chen, P. Wagner, L. Tong, G. G. Wallace, D. L. Officer, G. F. Swiegers – A Porphyrin-Doped Polymer Catalyzes Selective, Light-Assisted Water Oxidation in Seawater – Angew. Chem. Int. Ed. 2012, 51, 1907. [2] D. Khusnutdinova, B. L. Wadsworth, M. Flores, A. M. Beiler, E. A. Reyes Cruz, Y. Zenkov, G. F. Moore – Electrocatalytic Properties of Binuclear Cu(II) Fused Porphyrins for Hydrogen Evolution – ACS Catal. 2018, 8, 9888. [3] G. Bengasi, K. Baba, G. Frache, P. Gratia, K. Heinze, N. D. Boscher – Conductive Fused Porphyrin Tapes on Sensitive Substrates by a Chemical Vapor Deposition Approach – Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201814034. Figure 1

Conductive Fused Porphyrin Tapes on Sensitive Substrates by a Chemical Vapor Deposition Approach

AbstractOxidative polymerization of nickel(II) 5,15‐diphenyl porphyrin and nickel(II) 5,15‐bis(di‐3,5‐tert‐butylphenyl) porphyrin by oxidative chemical vapor deposition (oCVD) yields multiply fused porphyrin oligomers in thin film form. The oCVD technique enables one‐step formation, deposition, and p‐doping of conjugated poly(porphyrins) coatings without solvents or post‐treatments. The decisive reactions and side reactions during the oCVD process are shown by high‐resolution mass spectrometry. Owing to the highly conjugated structure of the fused tapes, the thin films exhibit an electrical conductivity of 3.6×10−2 S cm−1 and strong absorption in the visible to near‐infrared spectral region. The formation of smooth conjugated poly(porphyrins) coatings, even on sensitive substrates, is demonstrated by deposition and patterning on glass, silicon, and paper. Formation of conductive poly(porphyrins) thin films could enable the design of new optoelectronic devices using the oCVD approach.

Conductive Fused Porphyrin Tapes on Sensitive Substrates by a Chemical Vapor Deposition Approach.

Oxidative polymerization of nickel(II) 5,15‐diphenyl porphyrin and nickel(II) 5,15‐bis(di‐3,5‐tert‐butylphenyl) porphyrin by oxidative chemical vapor deposition (oCVD) yields multiply fused porphyrin oligomers in thin film form. The oCVD technique enables one‐step formation, deposition, and p‐doping of conjugated poly(porphyrins) coatings without solvents or post‐treatments. The decisive reactions and side reactions during the oCVD process are shown by high‐resolution mass spectrometry. Owing to the highly conjugated structure of the fused tapes, the thin films exhibit an electrical conductivity of 3.6×10−2 S cm−1 and strong absorption in the visible to near‐infrared spectral region. The formation of smooth conjugated poly(porphyrins) coatings, even on sensitive substrates, is demonstrated by deposition and patterning on glass, silicon, and paper. Formation of conductive poly(porphyrins) thin films could enable the design of new optoelectronic devices using the oCVD approach.

Frontispiece: Triply Linked Porphyrinoids

The triply linked porphyrin array (porphyrin tape) and recent additions to the triply linked porphyrinoid family including corrole tape, porphyrin-hexaphyrin hybrid tape, subporphyrin tape, and porphyrin arch-tape are highlighted in the graphic. These tape-like molecules can be regarded as polycyclic aromatic molecules, but their optical and electrochemical properties are particularly fascinating, encouraging the study their structure–property relationships. Not only planar molecules, but also distorted structures have been made owing to the development of new synthetic methods. For a full discussion see the Minireview article by T. Tanaka and A. Osuka on page 17188 ff.

Triply Linked Porphyrinoids.

Triply linked porphyrin arrays, so called porphyrin tapes, are intriguing molecules in terms of their planar structures, far red-shifted absorption bands, multi-charge storage abilities, and high conductivities. Recently, porphyrin tape variants such as porphyrin-expanded porphyrin hybrid tapes, porphyrin arch-tapes, corrole tapes, and a subporphyrin tape have been explored as novel π-conjugated materials. These new molecules exhibit electronic and structural characteristics owing to direct triple linkages. This Minireview first discusses the fundamental properties of the parent porphyrin tapes and the peripherally functionalized porphyrin tapes. Then, a focus has been placed on the syntheses, structures, and unique properties of the recently explored porphyrin tape variants.

Bias-Driven Conductance Increase with Length in Porphyrin Tapes.

A key goal in molecular electronics has been to find molecules that facilitate efficient charge transport over long distances. Normally, molecular wires become less conductive with increasing length. Here, we report a series of fused porphyrin oligomers for which the conductance increases substantially with length by >10-fold at a bias of 0.7 V. This exceptional behavior can be attributed to the rapid decrease of the HOMO-LUMO gap with the length of fused porphyrins. In contrast, for butadiyne-linked porphyrin oligomers with moderate inter-ring coupling, a normal conductance decrease with length is found for all bias voltages explored (±1 V), although the attenuation factor (β) decreases from ca. 2 nm-1 at low bias to <1 nm-1 at 0.9 V, highlighting that β is not an intrinsic molecular property. Further theoretical analysis using density functional theory underlines the role of intersite coupling and indicates that this large increase in conductance with length at increasing voltages can be generalized to other molecular oligomers.