Relationship between two-photon absorption and the pi-conjugation pathway in porphyrin arrays through dihedral angle control

Recently, covalently linked or self-assembled porphyrin array systems have attracted much attention for their enhanced two-photon absorption (TPA) behaviors. In this study, we have investigated the TPA properties of various dihedral angle controlled, directly linked porphyrin dimers and arrays to elucidate the relationship between the pi-conjugation pathway and TPA properties. We have demonstrated a strong correlation between pi-conjugation (aromaticity) and TPA properties in porphyrin assemblies.     

Charge transfer enhances two-photon absorption in transition metal porphyrins

Two-photon absorption processes were investigated in electropolymerized Fe(III), Mn(III), and Co(II) 5,10,15,20-tetrakis-(4-hydroxytetraphenyl)porphyrin films. Degenerate four wave mixing (DFWM) spectroscopy with 100 fs pulses in the near-IR spectral region was used. Metalloporphyrins with strong charge transfer (CT) transitions in the linear absorption spectra also show enhanced two-photon absorption. (Metalloporphyrin two-photon absorption cross section, delta, increases >10 times over that for the metal free porphyrin.) This effect was attributed to a two-photon induced charge transfer between the metal ion's d orbitals and the pi-system of the porphyrin. Correlation of one- and two-photon absorption properties of transition metal porphyrins suggests a new and simple approach to improve organic materials for photonic applications.     

Enhancement of two-photon absorption cross section and singlet-oxygen generation in porphyrin-cored star polymers

We report a newly synthesized polymer of a star-shaped porphyrin compound(TPA-FxP) with four oligofluorene arms at its meso positions with the pronounced enhancement of the two-photon properties and the generation of singlet oxygen by utilizing the two-photon excited fluorescence resonance energy transfer.The steady-state spectra and transient triplet-triplet absorption spectra give evidence that the enhanced two-photon absorption cross section results from not only the through-space energy transfer(Frster...     

Singlet oxygen generation via two-photon excited FRET

A new approach to two-photon excited photodynamic therapy has been developed. A dendritic array of eight donor chromophores capable of two-photon absorption (TPA) was covalently attached to a central porphyrin acceptor. Steady-state fluorescence measurements demonstrated that the donor chromophores transfer excited-state energy to the porphyrin with 97% efficiency. Two-photon excitation of the donor chromophores at 780 nm resulted in a dramatic increase in porphyrin fluorescence relative to a porphyrin model compound. Enhanced singlet oxygen luminescence was observed from oxygen-saturated solutions of the target compound under two-photon excitation conditions.     

Influence of carbohydrate biological vectors on the two-photon resonance of porphyrin oligomers

We propose a spectroscopic study of π-conjugated porphyrin dimers and a triphenylamine centered trimer bearing monoethyleneglycol-peracetylated α-mannose targeting moieties, which were synthesized for application to two-photon absorption photodynamic therapy (2PA-PDT). The collected spectroscopic data are explained through comparison with previous results obtained on similar nonvectorized analogues. It appears that the different shifts and variations in linear and nonlinear absorption and emission bands are mainly due to an increased twist between the tetrapyrrolic units. The 2PA properties of the triphenylamine-centered trimer have been studied, and two fluorescence emission bands are observed that seem to originate from two different 2PA excitation pathways. These results have important implication for the design of new vectorized photosensitizers for 2PA-PDT.     

Effects of carbon-metal-carbon linkages on the optical, photophysical, and electrochemical properties of phosphametallacycle-linked coplanar porphyrin dimers

5-(Diphenylphosphanyl)-10,15,20-triarylporphyrins (meso-phosphanylporphyrins) underwent complexations with palladium(II) and platinum(II) salts to afford phosphapalladacycle- and phosphaplatinacycle-fused coplanar porphyrin dimers, respectively, via regioselective peripheral β-C-H activation of the meso-phosphanylporphyrin ligands. The optical and electrochemical properties of these metal-linked porphyrin dimers as well as their porphyrin monomer/dimer references were investigated by means of steady-state UV-vis absorption/fluorescence spectroscopy, cyclic and differential pulse voltammetry, time-resolved spectroscopy (fluorescence and transient absorption lifetimes and spectra), and magnetic circular dichroism spectroscopy. All the observed data clearly show that the palladium(II) and platinum(II) linkers play crucial roles in the electronic communication between two porphyrin chromophores at the one-electron oxidized state and in the singlet-triplet intersystem-crossing process at the excited state. It has also been revealed that the C-Pt-C linkage makes more significant impacts on these fundamental properties than the C-Pd-C linkage. Furthermore, density functional theory calculations on the metal-linked porphyrin dimers have suggested that the antibonding dπ-pπ orbital interaction between the peripherally attached metal and adjacent pyrrolic β-carbon atoms destabilizes the highest occupied molecular orbitals of the porphyrin π-systems and accounts for the observed unique absorption properties. On the basis of these experimental and theoretical results, it can be concluded that the linear carbon-metal-carbon linkages weakly but definitely perturb the optical, photophysical, and electrochemical properties of the phosphametallacycle-linked coplanar porphyrin dimers.     

苯环上取代基的性质对双卟啉分子内能量转移的影响

金属卟啉在光合作用中起重要作用,合成其聚合物并作为光合作用模拟体系研究其能量转移和电子转移过程,已成为化学领域的重要研究课题之一.用于光合作用活性中心模拟体的金属卟啉聚合物种类很多,本文参考Little方法合成2种未见报道的苯环上分别带推电子和拉电子取代基和以柔韧碳氢链相连的中位双卟啉p-ZnTPP/p-H_2TMPP和p-ZnTPP/p-H_2TCPP(图1),探索了取     

Enlarged pi-electronic network of a meso-meso, beta-beta, beta-beta triply linked dibenzoporphyrin dimer that exhibits a large two-photon absorption cross section

Enlargement of the pi-electronic network of meso-meso, beta-beta, beta-beta triply linked diporphyrin has been exploited by preparing a corresponding dibenzo-fused porphyrin dimer that exhibits a perturbed absorption spectrum and a large two-photon absorption cross section.     

Enhancement of two-photon absorption cross-section and singlet-oxygen generation in porphyrins upon beta-functionalization with donor-acceptor substituents

The microwave-enhanced synthesis, comparative singlet oxygen sensitization efficiency, and nonlinear optical characterization of a new beta-functionalized porphyrin and its copper complex are described. We show that the introduction of a donor-acceptor push-pull conjugated fragment in the beta position strongly perturbs the porphyrin electronic structure leading to a remarkable one- and two-photon NIR absorption enhancement.     

Helicity induction and two-photon absorbance enhancement in zinc(II) meso-meso linked porphyrin oligomers via intermolecular hydrogen bonding interactions

Helicity has been induced in meso-meso linked oligomers by hydrogen bonding host-guest interactions with cyclic urea. Helical porphyrin arrays thus formed exhibit chirality amplification and enhanced two-photon absorption properties.     

Very large infrared two-photon absorption cross section of asymmetric zinc porphyrin aggregates: Role of intermolecular interaction and donor-acceptor strengths

Very large two-photon absorption (TPA) cross sections at the infrared region have been revealed for J-aggregates of asymmetric zinc porphyrin using quantum-chemical calculation. The TPA properties are evaluated for monomer and aggregates of a series of push-pull porphyrins, whose syntheses are known in the literature. The two-photon absorption cross section can be greatly enhanced by increasing the strengths of the electron donor/acceptor. We also present a quantum-chemical analysis on porphyrin aggregates to understand the role of intermolecular interactions and the relationship between structural and collective nonlinear optical properties. It has been observed that the TPA properties change tremendously as monomers undergo J-aggregation and the magnitudes of TPA cross sections are highly dependent on the nature of aggregates. The importance of our results with respect to the design of photonic and photodynamic therapy materials has been discussed.     

Charge transfer induced enhancement of near-IR two-photon absorption of 5,15-bis(azulenylethynyl) zinc(II) porphyrins

Intramolecular charge transfer in 5,15-bis(azulenylethynyl) substituted zinc(ii) porphyrin leads to a significant enhancement of two-photon absorption at near-IR region, which has been investigated by femtosecond Z-scan method.     

Syntheses of vinyl polymers with pendant porphyrin dimers and their catalytic effects on photoreductions

Vinyl copolymers with pendant porphyrin dimers were synthesized first by the dimerizations of chlorophyll-α and protoporphyrin IX via the ethylenebisamide linkage, then by copolymerization of the vinylbenzyl esters of the resulting dimers with N-vinylpyrrolidone or the esterification reaction of the dimers with chloromethylstyrene copolymers. Dimer-pendant copolymers with vinyl pyrrolidone catalyzed photoredox systems in aqueous solutions more efficiently than the corresponding monomer analogs, presumably because of the interactions exerted between the two combined porphyrin rings, which are manifested in the hypochromic effect in absorption spectra. The effect of the central Mg atom in the protoporphyrin IX ring was also considerable.     

Core-modified expanded porphyrins with large third-order nonlinear optical response

The third-order nonlinear optical response through measurement of two-photon absorption cross-sections (TPACS) for aromatic core-modified expanded porphyrin analogues by a femtosecond open aperture Z-scan method is reported. The values reported here are among the largest known so far in the literature for any organic molecules.     

Excited-state properties of water-soluble porphyrin dimers

The excited-state properties of heterodimers oftetra(4-carboxyphenyl)porphyrin (TPPC) and tetra(N-methylpyridyl) porphyrin (TMPyP) are studied by absorption and emission spectroscopy, EPR and zero-field ODMR. The excited singlet and triplet states of dimers formed by pairing H₂TPPC with H₂TMPyP or ZnTMPyP are localized on H₂TPPC. The dimers formed by pairing H₂TPPC with CuTMPyP and H₂TMPyP with ZnTPPC or CuTPPC are non-fluorescent due to intramolecular electron transfer.     

Two-photon absorption properties of self-assemblies of butadiyne-linked bis(imidazolylporphyrin)

Supramolecular porphyrin self-assemblies have been prepared from butadiyne-linked bis(imidazolylporphyrin) by complementary coordination of imidazole to zinc, and their two-photon absorption (2PA) and higher-order nonlinear absorption properties were investigated over femtosecond time scales using an open-aperture Z-scan method. The self-assembled porphyrin dimer of the conjugated monozinc bisporphyrin 7D was shown to have a large 2PA cross section (7.6 x 10(3) GM, where 1 GM = 10(-50) cm(4) s molecule(-1) photon(-1)) at 887 nm. By comparison of this result with that for a meso-meso-linked porphyrin array without the butadiyne connection (3.7 x 10(2) GM at 964 nm), it was demonstrated that the predominant factor in this significant enhancement of the cross section was the expansion of porphyrin-porphyrin pi-conjugation. Self-coordination and monozinc metalation were also found to be contributing factors. Furthermore, a novel self-assembled porphyrin polymer 8P consisting of a biszinc complex with a mean molecular weight of M(n) = 1.5 x 10(5) Da was shown to exhibit an extraordinarily large two-photon absorption cross section (4.4 x 10(5) GM at 873 nm). Nanosecond Z-scan experiments for 7D and 8P were also undertaken and resulted in the measurement of large effective 2PA cross sections, including the excited-state absorption (2.1 x 10(5) GM for 7D and 2.2 x 10(7) GM for 8P, respectively). Finally, three-photon absorption was observed by femtosecond Z-scan experiments at 1188 nm (7.1 x 10(-89) m(6) s(2)) and 1282 nm (1.8 x 10(-89) m(6) s(2)), an observation which is the first of its kind in porphyrin chemistry.     

Influence of the central metal ion on nonlinear optical and two-photon absorption properties of push-pull transition metal porphyrins

We present a quantum-chemical analysis of the central metal ion's effect on first hyperpolarizabilities and two-photon absorption (TPA) cross sections at the infrared region of a series of push-pull porphyrins whose synthesis and NLO properties have been reported earlier (J. Am. Chem. Soc. 2005, 127, 9710). The molecular geometries are obtained via the B3LYP/6-31G(d,p) level optimization including SCRF/PCM approach, and the NLO and TPA properties are calculated with the ZINDO/CV method including solvent effects. It is found that the CT transition between the metal ion's d orbital and the macrocycle pi orbitals plays an important role on NLO and TPA properties of metal porphyrins. Our data suggest a new approach to enhance TPA properties of porphyrin materials. We also present a quantum-chemical analysis on porphyrin dimers and trimers to understand the relationship between structural and collective NLO properties. It has been observed that beta values can be improved about an order of magnitude and TPA properties can be enhanced by 2 orders of magnitude by the formation of a trimer. The importance of our results with respect to the design of photonic and photodynamic therapy materials have been discussed.     

Tetrakis(4-tert-butylphenyl) substituted and fused quinoidal porphyrins

4-tert-Butylphenyl-substituted and fused quinoidal porphyrins 1 and 2 are prepared for the first time. They show (1) intense one-photon absorption in the far-red/near-infrared region, (2) enhanced two-photon absorption compared with aromatic porphyrin monomers, and (3) amphoteric redox behavior. Their geometry and electronic structure are studied by DFT calculations.