Synthesis of mono- and disubstituted porphyrins: A- and 5,10-A2-type systems

General syntheses have been developed for meso-substituted porphyrins with one or two substituents in the 5,10-positions and no beta substituents. 5-Substituted porphyrins with only one meso substituent are easily prepared by an acid-catalyzed condensation of dipyrromethane, pyrrole-2-carbaldehyde, and an appropriate aldehyde using a "[2+1+1]" approach. Similarly, 5,10-disubstituted porphyrins are accessible by simple condensation of unsubstituted tripyrrane with pyrrole and various aldehydes using a "[3+1]" approach. The yields for these reactions are low to moderate and additional formation of either di- or monosubstituted porphyrins due to scrambling of the intermediates is observed. However, the reactions can be performed quite easily and the desired target compounds are easily removed due to large differences in solubility. A complementary and more selective synthesis involves the use of organolithium reagents for S(N)Ar reactions. Reaction of in situ generated porphyrin (porphine) with 1.1-8 equivalents of RLi gave the monosubstituted porphyrins, while reaction with 3-6 equivalents of RLi gave the 5,10-disubstituted porphyrins in yields ranging from 43 to 90 %. These hitherto almost inaccessible compounds complete the series of different homologues of A-, 5,15-A(2)-, 5,10-A(2)-, A(3)-, and A(4)-type porphyrins and allow an investigation of the gradual influence of type, number, and regiochemical arrangement of substituents on the properties of meso-substituted porphyrins. They also present important starting materials for the synthesis of ABCD porphyrins and are potential synthons for supramolecular materials requiring specific substituent orientations.     

手性联萘桥联双卟啉的电子光谱与二阶非线性光学性质

在6-31G(d,p)水平上用B3LYP方法对手性联萘桥联双卟啉系列分子进行几何构型优化. 用半经验ZINDO/S方法计算了这些分子的电子光谱, 结果表明手性联萘桥联双卟啉中两个卟啉生色团之间存在强的激子耦合作用, B带的Davydov分裂大小与两个卟啉环的相对取向以及卟啉环中心之间距离有关. 用ZINDO/SOS方法计算了分子的一阶超极化率. 卟啉环上引入推/拉电子基团可以有效地提高手性联萘桥联双卟啉的二阶非线性光学系数. 一阶超极化率的大小与双卟啉中推/拉电子基团的空间排列方式有关. 一阶超极化率的提高不仅与分子激发态与基态偶极矩差增大有关, 还和基态偶极矩与激子耦合激发态跃迁矩矢量的相对取向密切相关.     

Directly meso-meso linked porphyrin rings: synthesis, characterization, and efficient excitation energy hopping

Directly meso-meso linked porphyrin rings CZ4, CZ6, and CZ8 that respectively comprise four, six, and eight porphyrins have been synthesized in a stepwise manner from a 5,10-diaryl zinc(II) porphyrin building block. Symmetric cyclic structures have been indicated by their very simple (1)H NMR spectra that exhibit only a single set of porphyrin and their absorption spectra that display a characteristic broad nonsplit Soret band around 460 nm. Energy minimized structures calculated at the B3LYP/6-31G* level indicate that a dihedral angle between neighboring porphyrins decreases in order of CZ6 > CZ8 > CZ4, which is consistent with the (1)H NMR data. Photophysical properties of these molecules have been examined by the steady-state absorption, fluorescence, fluorescence lifetime, fluorescence anisotropy decay, and transient absorption measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly related with the excitation energy migration processes within the porphyrin rings, where the exciton-exciton annihilation time and the polarization anisotropy rise time are well described in terms of the Forster-type incoherent energy hopping model. Consequently, the excitation energy hopping rates have been estimated for CZ4 (119 +/- 2 fs)(-)(1), CZ6 (342 +/- 59 fs)(-)(1), and CZ8 (236 +/- 31 fs)(-)(1), which reflect the magnitude of the electronic coupling between the neighboring porphyrins. Overall, these porphyrin rings serve as a well-defined wheel-shaped light harvesting antenna model in light of very efficient excitation energy hopping along the ring.     

Raman and infrared spectral study of meso-sulfonatophenyl substituted porphyrins (TPPSn,n = 1, 2A, 2O, 3, 4)

Raman and IR spectra of the free base p-sulfonatophenyl and phenyl meso-substituted porphyrins [5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4); 5,10,15-tris(4-sulfonatophenyl)-20-phenyl-porphyrin (TPPS3); 5,10-bis(4-sulfonatophenyl)-15,20-diphenylporphyrin (TPPS2A); 5,15-bis(4-sulfonatophenyl)-10,20-diphenylporphyrin (TPPS2O); and 5-(4-sulfonatophenyl)-10, 15,20-trisphenylporphyrin (TPPS1)] and their N-diprotonated derivatives (porphyrin diacids) were studied. The Raman spectra of the deuterated analogues of these porphyrins, in which the central hydrogen atoms were substituted with deuterium, were also measured. The observed vibrational bands were assigned on the basis of the deuteration shifts and compared with the structural analogues of these compounds. In IR spectra of the free-base porphyrins, the p-sulfonation of phenyl groups results in evident alteration for the phenyl modes and the porphyrin skeleton modes that are strongly coupled with phenyl vibrations. While the p-sulfonation of phenyl groups causes only slight changes for the high-frequency Raman bands (> 850 cm(-1)), dramatic shifts and band splitting were observed in the low-frequency region (< 500 cm(-1)) of Raman spectra. The observed differences of low-frequency Raman spectra were attributed to the alteration of the structure of the porphyrin ring, especially the CalphaCmCalpha bond-angles, by different meso-sulfonatophenyl substitutions. In addition, different packing style of TPPSn molecules in the aggregates is also responsible for the alteration of the vibrational spectra of the aggregated TPPSn.     

Synthesis of porphyrins bearing uracyl groups and their assembly induced by melamine derivatives

Self‐assembled porphyrins via noncovalent bonding have attracted wide‐ranging researchers in material science. We reported herein the synthesis of the tetraphenyl porphyrin derivatives bearing uracyl groups as acceptor–donor–acceptor (ADA) type hydrogen bonding units, through the condensation of 5,10‐ or 5,15‐bis (3‐amino‐4‐ethylhexylphenyl) porphyrin derivatives with 6‐carboxyuracyl derivatives. When two porphyrins having uracyl groups at the different substituted positions were respectively mixed with a melamine derivative in benzene, ¹H NMR spectra showed that the 5,15 substituted uracyl porphyrin formed a hydrogen‐bonded suprastructure with the melamine derivative as a complementary molecule to the uracyl moiety, although the other 5,10‐substituted uracylporphyrin could not form such a structure. The SEM observation indicated that the mixture with the 5,15‐substituted uracyl porphyrin and the melamine with long alkyl chains formed a sheet‐like structure. Copyright © 2007 John Wiley & Sons, Ltd.     

Masked imidazolyl-dipyrromethanes in the synthesis of imidazole-substituted porphyrins

Imidazole-substituted metalloporphyrins are valuable for studies of self-assembly and for applications where water solubility is required. Rational syntheses of porphyrins bearing one or two imidazol-2-yl or imidazol-4-yl groups at the meso positions have been developed. The syntheses employ dipyrromethanes, 1-acyldipyrromethanes, and 1,9-diacyldipyrromethanes bearing an imidazole group at the 5-position. The polar, reactive imidazole unit was successfully masked by use of (1) the 2-(trimethylsilyl)ethoxymethyl (SEM) group at the imidazole pyrrolic nitrogen, and (2) a dialkylboron motif bound to the pyrrole of the dipyrromethane and coordinated to the imidazole imino nitrogen. The nonpolar nature of such doubly masked imidazolyl-dipyrromethanes facilitated handling. Selected masked dipyrromethanes were characterized by 11B and 15N NMR spectroscopy. Five distinct methods were examined to obtain trans-A2B2-, trans-AB2C-, and trans-AB-porphyrins. Each porphyrin contained one or two SEM-protected imidazole units. The SEM group could be removed with TBAF or HCl. Two zinc(II) porphyrins and a palladium(II) porphyrin bearing a single imidazole moiety were prepared and subjected to alkylation (with ethyl iodide, 1,3-propane sultone, or 1,4-butane sultone) to give water-soluble imidazolium- porphyrins. This work establishes the foundation for the rational synthesis of a variety of porphyrins containing imidazole units.     

Surface patterning with two-dimensional porphyrin supramolecular arrays

Monolayer arrays of a series of meso-tetra-substituted porphyrins containing octadecyloxy and carboxyl (or pyridyl) groups were prepared on the highly oriented pyrolytic graphite surface at the liquid/solid interface. It was found by means of scanning tunneling microscopy that some porphyrins from this family assemble into various patterns. Specifically, slightly undulated rows are obtained from 5,10,15-tris(4-octadecyloxyphenyl)-20-(4-pyridyl)porphyrin. Meanwhile, rows with more pronounced kinks result from 5-(4-carboxyphenyl)-10,15,20-tris(4-octadecyloxyphenyl)porphyrin. The occurrence of the kinks is dependent on the arrangement of surrounding porphyrin molecules and is determined by intricate interplay between directional hydrogen-bonding interactions and packing forces, including molecule-molecule and molecule-substrate interactions. A double-layer structure is obtained from 5,10-bis(4-carboxyphenyl)-15,20-bis(4-octadecyloxyphenyl)porphyrin, probably through cyclic hydrogen bond formation. This work proves the concept that programmed surface patterning is possible by using porphyrins incorporating directional intermolecular interaction sites.     

Photodynamic studies and photoinactivation of Escherichia coli using meso-substituted cationic porphyrin derivatives with asymmetric charge distribution

The photodynamic activities of novel asymmetrically meso-substituted cationic porphyrins, 5,10-di(4-methylphenyl)-15,20-di(4-trimethylammoniumphenyl)porphyrin iodide 1 and 5-(4-trifluorophenyl)-10,15,20-tris(4-trimethylammoniumphenyl)porphyrin iodide 2 and its metal complex with Pd(II) 3, have been investigated in both homogeneous medium bearing photooxidizable substrates and in vitro on a typical gram-negative bacterium Escherichia coli. The amphiphilic character of porphyrin 2 was increased by the presence of a high-lipophilic trifluoromethyl group and its photophysical properties changed by forming a complex with Pd(II). Absorption and fluorescence spectroscopic studies were compared in different media. Fluorescence quantum yields (phi(F)) of 0.16 for 1 in tetrahydrofuran and 0.08 for 2 in N, N-dimethylformamide (DMF) were calculated, whereas no significant emission was detected for Pd(II) porphyrin 3. The singlet molecular oxygen, O(2)((1)Delta(g)), production was evaluated using 9,10-dimethylanthracene in DMF yielding relative values of 1, 0.55 and 0.47 for porphyrins 3, 2 and 1, respectively. A faster decomposition of l-tryptophan was obtained using Pd(II) porphyrin 3 as sensitizer with respect to the free-base porphyrins 1 and 2. In biological medium, the behavior of cationic porphyrins 1-3 were compared with that of 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin 4, which was used as a noncationic sensitizer. These porphyrins are rapidly bound to E. coli cells in 5 min and the amount of cell-bound sensitizer is not appreciably changed incubating the cultures for longer times. The recovered porphyrin 2 after one washing step reaches a value of approximately 2.9 nmol/10(6) cells and this amount remains high even after three washes, indicating that this sensitizer is tightly bound to cells. Photosensitized inactivation of E. coli was analyzed using cells without and with one washing step. In both cases, a higher photoinactivation of cells was found for tricationic porphyrin 2 and 3, causing a approximately 5.5 log (99.999%) decrease of cell survival, when treated with 10 microM of sensitizer. Under these conditions, a lower effect was found for porphyrin 1 (approximately 4 log) whereas sensitizer 4 did not produce appreciable photodamage. The results were also confirmed by growth delay experiments. These studies show that the amphiphilic tricationic porphyrin 2 and 3 bearing a trifluoromethyl group can be a promising model for phototherapeutic agents with potential applications in inactivation of bacteria by photodynamic therapy.     

Strong two-photon absorption in new asymmetrically substituted porphyrins: interference between charge-transfer and intermediate-resonance pathways

We study two-photon absorption (2PA) in two series of new free-base porphyrins with 4-(diphenylamino)stilbene or 4,4'-bis-(diphenylamino)stilbene (BDPAS) attached via pi-conjugating linkers at the porphyrin meso-position. We show that this new substitution modality increases the 2PA cross section in the Soret band region (excitation wavelength 750-900 nm) of the core porphyrin by nearly 2 orders of magnitude, from sigma(2) approximately 10 GM for the meso-phenyl-substituted analogue to sigma(2) approximately 10(3) GM for the ethynyl-linked BDPAS-porphyrin dyad. The 2PA properties are quantitatively described by considering two different and interfering 2PA quantum transition pathways. The first path involves virtual transition via intermediate one-photon resonance. The second path bypasses the intermediate resonance and occurs due to a large permanent dipole moment difference between the ground and the final electronic states. To our best knowledge, this is the first experimental observation of the combined effect of these two pathways on one particular two-photon transition, resulting in quantum-interference-modulated 2PA strength.     

The synthesis and studies towards the self-replication of bis(capped porphyrins)

Connecting two facially-protected porphyrins was expected to lead to an equal mixture of laterally-bridged doubly-protected bis-porphyrins; one in which the two porphyrin units were protected on the same face (syn) and one with the two prophyrin units protected on opposite faces (anti). Addition of a co-factor (bidentate ligand) was expected to lead predominantly to the syn-bis-porphyrin by a templated self-replication process. This concept was explored using Baldwin's capped porphyrin. Bis(capped porphyrins) were synthesised in several steps starting from zinc(II) capped porphyrin 2. Nitration of 2 followed by reduction and photo-oxidation yields a mixture of zinc(II) porphyrindiones 7 and 8 that can separated by HPLC. The condensation of 2 molar eq. of zinc(II) porphyrin-7,8-dione 8 with 1,2,4,5-benzenetetramine leads to the formation of a 1:1 mixture of syn- and anti-dizinc(II) bis(7,8-capped porphyrins), 11 and 12, respectively, that have almost identical spectroscopic properties. These two geometric isomers were distinguished by significant differences in their molecular recognition properties. Likewise the syn- and anti-dizinc(II) bis(2,3-capped porphyrins), 9 and 10, respectively, are synthesised from the related zinc(II) capped porphyrin-2,3-dione 7, and were also identified using molecular recognition studies. The molecular recognition properties of these bis(capped porphyrins) were utilised in studies of self-replicating porphyrin systems. The results show that tetraazaanthraceno-bis-porphyrins 9-12 can catalyse their own formation but self-replication was not observed. These results highlight the potential that these interesting hosts have as templates in supramolecular chemistry, synthesis and catalysis.     

Fluorescent tetraruthenated porphyrins embedded in monolithic SiO2 gels by the sol-gel process

In this work silica gels have been prepared by a sol-gel method using tetraethylorthosilicate as gel precursor. The tetraruthenated porphyrins H2(3-TRPyP), Co(3-TRPyP), and H2(4-TRPyP) were incorporated into the systems during gel formation without problems commonly found in the process, such as aggregation. Spectroscopic studies of the resulting silica gels revealed the presence of absorption bands in the range 200-400 nm associated with the transitions of the groups ruthenium-bipyridine, along with the Soret band at the same wavelengths observed in solution. The porphyrins were found to preserve fluorescence emission properties in the range 650-700 nm even after the aging period. Study of the thermal behavior and decomposition kinetics evidenced that the porphyrin H2(4-TRPyP) is the least stable of the group and that all compounds decompose according to first-order kinetics.     

A2B2-type push-pull porphyrins as reverse saturable and saturable absorbers

A(2)B(2)-type push-pull porphyrins with a strong intramolecular dipole moment have been prepared via Heck and Suzuki coupling reactions as novel materials for use in nonlinear optics (NLO); they display saturable (SA) and reverse saturable absorption (RSA) properties at 532 nm and their nonlinear optical response is characterized by RSA occurring at lower intensity levels whereas the onset of SA prevails at higher levels.     

Synthesis of cyclic hexameric porphyrin arrays. Anchors for surface immobilization and columnar self-assembly

To investigate new architectures for the self-assembly of multiporphyrin arrays, a one-flask synthesis of a shape-persistent cyclic hexameric array of porphyrins was exploited to prepare six derivatives bearing diverse pendant groups. The new arrays contain 6-12 carboxylic acid groups, 12 amidino groups, 6 thiol groups, or 6 thiol groups and 6 carboxylic acid groups in protected form (S-acetylthio, TMS-ethyl, TMS-ethoxycarbonyl). The arrays contain alternating Zn and free base (Fb) porphyrins or all Zn porphyrins. The one-flask synthesis entails a template-directed, Pd-mediated coupling of a p/p'-substituted diethynyl Zn porphyrin and a m/m'-substituted diiodo Fb porphyrin. The porphyrin building blocks (trans-A(2)B(2), trans-AB(2)C) contain the protected pendant groups at nonlinking meso positions. A self-assembled monolayer (SAM) of a Zn(3)Fb(3) cyclic hexamer containing one thiol group on each porphyrin was prepared on a gold electrode and the surface-immobilized architecture was examined electrochemically. Together, the work reported herein provides cyclic hexameric porphyrin arrays for studies of self-assembly in solution or on surfaces.     

Push–Pull Porphyrins via β-Pyrrole Functionalization: Evidence of Excited State Events Leading to High-Potential Charge-Separated States

A new set of free-base and zinc(II)-metallated, β-pyrrole-functionalized unsymmetrical push–pull porphyrins were designed and synthesized via β-mono- and dibrominated tetraphenylporphyrins using Sonogashira cross-coupling reactions. The ability of donors and acceptors on the push–pull porphyrins to produce high-potential charge separated states was investigated. The porphyrins were functionalized at the opposite β,β′-pyrrole positions of porphyrin ring bearing triphenylamine push groups and naphthalimide pull groups. Systematic studies involving optical absorption, steady-state and time-resolved emission revealed existence of intramolecular type interactions both in the ground and excited states. The push–pull nature of the molecular systems was supported by frontier orbitals generated on optimized structures, wherein delocalization of HOMO over the push group and LUMO over the pull group connecting the porphyrin π-system was witnessed. Electrochemical studies were performed to visualize the effect of push and pull groups on the overall redox potentials of the porphyrins. Spectroelectrochemical studies combined with frontier orbitals helped in characterizing the one-electron oxidized and reduced porphyrins. Finally, by performing transient absorption studies in polar benzonitrile, the ability of push–pull porphyrins to produce charge-separated states upon photoexcitation was confirmed and the measured rates were in the range of 10⁹ s⁻¹. The lifetime of the final charge separated state was around 5 ns. This study ascertains the importance of push–pull porphyrins in solar energy conversion and diverse optoelectronic applications, for which high-potential charge-separated states are warranted.     

Synthesis of Linear Amphipathic Porphyrin Dimers and Trimers: An Approach to Bilayer Lipid Membrane Spanning Porphyrin Arrays

A modular building-block approach has been developed for the construction of linear amphipathic porphyrin arrays. The reaction of meso-(trifluoromethyl)dipyrromethane and an aldehyde under the conditions of the two-step room temperature porphyrin synthesis affords the trans-substituted porphyrin (13-56% yields). A similar reaction with two different aldehydes provides access to porphyrins bearing two different functional groups. An ethyne porphyrin and an iodo porphyrin (either free base or zinc) are selectively joined via Pd(0)-catalyzed coupling reactions, affording a linear array with porphyrins in defined metalation states. Coupling of a zinc-porphyrin bearing iodo and ester groups with a free base porphyrin bearing ethyne and ester groups yielded the zinc-free base porphyrin dimer. Coupling of a bis-ethyne porphyrin with a porphyrin bearing iodo and ester groups afforded the porphyrin trimer. Cleavage of the esters yielded the amphipathic porphyrin dimer and trimer arrays. The arrays with adjacent zinc and free base porphyrins undergo efficient electronic energy transfer. Both amphipathic porphyrin arrays have been incorporated into L-alpha-phosphatidylcholine vesicles. This versatile synthetic strategy provides access to a family of porphyrin arrays for studies of photophysical processes in supramolecular assemblies.     

Photophysical properties of long rodlike meso-meso-linked zinc(II) porphyrins investigated by time-resolved laser spectroscopic methods

The molecular design of directly meso-meso-linked porphyrin arrays as a new model of light-harvesting antenna as well as a molecular photonic wire was envisaged to bring the porphyrin units closer for rapid energy transfer. For this purpose, zinc(II) 5,15-bis(3,5-bis(octyloxy)phenyl)porphyrin (Z1) and its directly meso-meso-linked porphyrin arrays up to Z128 (Zn, n represents the number of porphyrins) were synthesized. The absorption spectra of these porphyrin arrays change in a systematic manner with an increase in the number of porphyrins; the high-energy Soret bands remain at nearly the same wavelength (413-414 nm), while the low-energy exciton split Soret bands are gradually red-shifted, resulting in a progressive increase in the exciton splitting energy. The exciton splitting is nicely correlated with the values of cos[pi/(N + 1)] according to Kasha's exciton coupling theory, providing a value of 4250 cm(-1) for the exciton coupling energy in the S(2) state. The increasing red-shifts for the Q-bands are rather modest. The fluorescence excitation anisotropy spectra of the porphyrin arrays show that the photoexcitation of the high-energy Soret bands exhibits a large angle difference between absorption and emission dipoles in contrast with the photoexcitation of the low-energy exciton split Soret and Q-bands. This result indicates that the high-energy Soret bands are characteristic of the summation of the individual monomeric transitions with its overall dipole moment deviated from the array chain direction, while the low-energy Soret bands result from the exciton splitting between the monomeric transition dipoles in line with the array chain direction. From the fluorescence quantum yields and fluorescence lifetime measurements, the radiative coherent length was estimated to be 6-8 porphyrin units in the porphyrin arrays. Ultrafast fluorescence decay measurements show that the S(2) --> S(1) internal conversion process occurs in less than 1 ps in the porphyrin arrays due to the existence of exciton split band as a ladder-type deactivation channel, while this process is relatively slow in Z1 (approximately 1.6 ps). The rate of this process seems to follow the energy gap law, which is mainly determined by the energy gap between the two Soret bands of the porphyrin arrays.     

Substituent-control exciton in J-aggregates of protonated water-insoluble porphyrins

A series of protonated porphyrin J-aggregates of various water-insoluble tetraphenylporphyrin derivatives was prepared by aggregation at the liquid-liquid or gas-liquid interface. Using atomic force microscopy, we observed microcrystalline porphyrin J-aggregates. The J-aggregates have two strong exciton bands corresponding to the B (Soret)- and Q-bands of the protonated porphyrin. Interestingly, the excitation energy of the lower exciton (denoted by S1) markedly depends on the meso-substituents, whereas that of the higher exciton (denoted by S2) does not depend on them. These results indicate that the nature of the exciton coupling of the S1 transition dipole moment can be systematically changed by the substituents.     

One-flask synthesis of mono- and trifunctionalized 21-thia and 21-oxaporphyrin building blocks and their application in the synthesis of covalent and noncovalent unsymmetrical porphyrin arrays

A rapid synthetic route has been developed to synthesize mono- and trifunctionalized 21-thia and 21-oxaporphyrin systems using simple precursors such as 2[alpha-(aryl)-alpha-hydroxymethyl] thiophene (thiophene mono-ol) and 2[alpha-(aryl)-alpha-hydroxymethyl] furan (furan mono-ol), respectively. Condensation of one equivalent of thiophene or furan mono-ol with two equivalents of aryl aldehyde and three equivalents of pyrrole under porphyrin forming conditions followed by column chromatography resulted in functionalized 21-thia or 21-oxaporphyrins. To synthesize monofunctionalized porphyrins, the mono-ol containing the functionalized aryl group was used. The functionalized aldehydes were used to synthesize trifunctionalized porphyrins. The mono-ol method is versatile and applicable to synthesize mono- and trifunctionalized 21-thia and 21-oxaporphyrins containing functional groups such as iodophenyl, ethynylphenyl, hydroxyphenyl, bromophenyl, and pyridyl groups. The monofunctionalized porphyrin building blocks containing iodophenyl and ethynylphenyl groups were used further to synthesize four unsymmetrical covalent porphyrin dimers containing two different porphyrin cores such as N3S-N4, N3O-N4, and N3S-N3O bridged via diaryl ethyne group and one symmetrical phenylethyne bridged dimer containing two N3S cores. A preliminary photophysical study on these dimers indicated a possibility of energy transfer from one subunit to another. We also demonstrated the use of trifunctionalized porphyrins in the synthesis of two noncovalent unsymmetrical porphyrin tetramers containing one N3S and three N4 porphyrin subunits.     

Three Short Stories about Hexaarylbenzene–Porphyrin Scaffolds

A feasible two‐step synthesis and characterization of a full series of hexaarylbenzene (HAB) substituted porphyrins and tetrabenzoporphyrins is presented. Key steps represent the microwave‐assisted porphyrin condensation and the statistical Diels–Alder reaction to the desired HAB‐porphyrins. Regarding their applications, they proved to be easily accessible and effective high molecular mass calibrants for (MA)LDI mass spectrometry. The free‐base and zinc(II) porphyrin systems, as well as the respective tetrabenzoporphyrins, demonstrate in solid state experiments strong red‐ and near‐infrared‐light emission and are potentially interesting for the application in “truly organic” light‐emitting devices. Lastly, they represent facile precursors to large polycyclic aromatic hydrocarbon (PAH) substituted porphyrins. We prepared the first tetra‐hexa‐peri‐hexabenzocoronene substituted porphyrin, which represents the largest prepared PAH‐porphyrin conjugate to date.