Synthesis and Characterization of a New Asymmetric Bis-Porphyrinato Lanthanide Complex Presenting Mixed Hydrophilic−Hydrophobic Properties and Its Precursor Form

The synthesis and spectroscopic characterization of a new family of heteroleptic porphyrinate double-deckers are reported. The investigated compounds are represented by the formulae LaIIIH(TPyP)(TPP) and [LaIII(TMePyP)(TPP)]I3. UV−vis spectroscopy of the title complexes confirms the presence of a strong π−π interaction between the macrocycles in each derivative. With 1H and 2-D NMR data, we were able to distinguish two major NMR regions:  the endo, between the bonded macrocycles, and the exo, outside the macrocycles, which are characteristic features of porphyrinic double-deckers. Finally, the electrochemical study confirms the strong π−π interaction for LaIIIH(TPyP)(TPP) and completes this first approach for the investigation of this new family of derivatives

Supramolecular Nanodrugs Constructed by Self-Assembly of Peptide Nucleic Acid–Photosensitizer Conjugates for Photodynamic Therapy

Two hybrid materials were designed by conjugating peptide nucleic acids (PNAs) to porphyrin or boron-dipyrromethene, generating PNA-porphyrin (PNA-TPP) and PNA-BODIPY (PNA-BDP) conjugates, respectively. Because of the combination of the supramolecular characteristics of PNAs and photosensitizers, the two hybrid conjugates readily self-assemble in aqueous solutions and produce well-defined nanoparticles with uniform particle sizes. The resulting two kinds of nanoparticles show good stability in biological solutions and upon dilution. Importantly, the nanoparticles can efficiently interact with cancer cells and the internalized nanoparticles are mainly distributed in the cytoplasm without discernible cytotoxicity in the dark, enabling them to be applied as photodynamic nanoagents for selective killing cells. Hence, self-assembly of PNA–photosensitizer conjugates may hold promise for advancing the rational design and construction of photodynamic nanoagents for cancer therapy

Meso-substituted Porphyrin Derivatives via Palladium-Catalyzed Amination Showing Wide Range Visible Absorption: Synthesis and Photophysical Studies

In recent years, there has been a growing interest in the design and synthesis of chromophores, which absorb in a wide region of the visible spectrum, as these constitute promising candidates for use as sensitizers in various solar energy conversion schemes. In this work, a palladium-catalyzed coupling reaction was employed in the synthesis of molecular triads in which two porphyrin or boron dipyrrin (BDP) chromophores are linked to the meso positions of a central Zn porphyrin (<b>PZn</b>) ring via an amino group. In the resulting conjugates, which strongly absorb over most of the visible region, the electronic properties of the constituent chromophores are largely retained while detailed emission experiments reveal the energy transfer pathways that occur in each triad

Electron vs Energy Transfer in Arrays Featuring Two Bodipy Chromophores Axially Bound to a Sn(IV) Porphyrin via a Phenolate or Benzoate Bridge

In this report we describe the synthesis of multichromophore arrays consisting of two Bodipy units axially bound to a Sn­(IV) porphyrin center either via a phenolate (3) or via a carboxylate (6) functionality. Absorption spectra and electrochemical studies show that the Bodipy and porphyrin chromophores interact weakly in the ground state. However, steady-state emission and excitation spectra at room temperature reveal that fluorescence from both the Bodipy and the porphyrin of 3 are strongly quenched suggesting that, in the excited state, energy and/or electron transfer might occur. Indeed, as transient absorption experiments show, selective excitation of Bodipy in 3 results in a rapid decay (τ ≈ 2 ps) of the Bodipy-based singlet excited state and a concomitant rise of a charge-separated state evolving from the porphyrin-based singlet excited state. In contrast, room-temperature emission studies on 6 show strong quenching of the Bodipy-based fluorescence leading to sensitized emission from the porphyrin moiety due to a transduction of the singlet excited state energy from Bodipy to the porphyrin. Emission experiments at 77 K in frozen toluene reveal that the room-temperature electron transfer pathway observed in 3 is suppressed. Instead, Bodipy excitation in 3 and 6 results in population of the first singlet excited state of the porphyrin chromophore. Subsequently, intersystem crossing leads to the porphyrin-based triplet excited state

Electron vs Energy Transfer in Arrays Featuring Two Bodipy Chromophores Axially Bound to a Sn(IV) Porphyrin via a Phenolate or Benzoate Bridge

In this report we describe the synthesis of multichromophore arrays consisting of two Bodipy units axially bound to a Sn­(IV) porphyrin center either via a phenolate (<b>3</b>) or via a carboxylate (<b>6</b>) functionality. Absorption spectra and electrochemical studies show that the Bodipy and porphyrin chromophores interact weakly in the ground state. However, steady-state emission and excitation spectra at room temperature reveal that fluorescence from both the Bodipy and the porphyrin of <b>3</b> are strongly quenched suggesting that, in the excited state, energy and/or electron transfer might occur. Indeed, as transient absorption experiments show, selective excitation of Bodipy in <b>3</b> results in a rapid decay (τ ≈ 2 ps) of the Bodipy-based singlet excited state and a concomitant rise of a charge-separated state evolving from the porphyrin-based singlet excited state. In contrast, room-temperature emission studies on <b>6</b> show strong quenching of the Bodipy-based fluorescence leading to sensitized emission from the porphyrin moiety due to a transduction of the singlet excited state energy from Bodipy to the porphyrin. Emission experiments at 77 K in frozen toluene reveal that the room-temperature electron transfer pathway observed in <b>3</b> is suppressed. Instead, Bodipy excitation in <b>3</b> and <b>6</b> results in population of the first singlet excited state of the porphyrin chromophore. Subsequently, intersystem crossing leads to the porphyrin-based triplet excited state

Electron vs Energy Transfer in Arrays Featuring Two Bodipy Chromophores Axially Bound to a Sn(IV) Porphyrin via a Phenolate or Benzoate Bridge

In this report we describe the synthesis of multichromophore arrays consisting of two Bodipy units axially bound to a Sn­(IV) porphyrin center either via a phenolate (3) or via a carboxylate (6) functionality. Absorption spectra and electrochemical studies show that the Bodipy and porphyrin chromophores interact weakly in the ground state. However, steady-state emission and excitation spectra at room temperature reveal that fluorescence from both the Bodipy and the porphyrin of 3 are strongly quenched suggesting that, in the excited state, energy and/or electron transfer might occur. Indeed, as transient absorption experiments show, selective excitation of Bodipy in 3 results in a rapid decay (τ ≈ 2 ps) of the Bodipy-based singlet excited state and a concomitant rise of a charge-separated state evolving from the porphyrin-based singlet excited state. In contrast, room-temperature emission studies on 6 show strong quenching of the Bodipy-based fluorescence leading to sensitized emission from the porphyrin moiety due to a transduction of the singlet excited state energy from Bodipy to the porphyrin. Emission experiments at 77 K in frozen toluene reveal that the room-temperature electron transfer pathway observed in 3 is suppressed. Instead, Bodipy excitation in 3 and 6 results in population of the first singlet excited state of the porphyrin chromophore. Subsequently, intersystem crossing leads to the porphyrin-based triplet excited state

N@C₆₀–Porphyrin: A Dyad of Two Radical Centers

Dyads of endohedral nitrogen fullerene and porphyrin have been synthesized. In the two-radical-center dyad, the copper­(II) tetraphenylporphyrin suppressed the electron spin resonance (ESR) signal of N@C₆₀ through intramolecular dipolar coupling with a strength of 27.0 MHz. Demetalation of the metalloporphyrin moiety of the dyad, which effectively turned the two-radical-center dyad into a single-radical-center dyad, recovered 82% of the ESR signal of N@C₆₀. Such mechanism of switching a spin state on and off could find use in molecular spintronics applications

Electron vs Energy Transfer in Arrays Featuring Two Bodipy Chromophores Axially Bound to a Sn(IV) Porphyrin via a Phenolate or Benzoate Bridge

In this report we describe the synthesis of multichromophore arrays consisting of two Bodipy units axially bound to a Sn­(IV) porphyrin center either via a phenolate (<b>3</b>) or via a carboxylate (<b>6</b>) functionality. Absorption spectra and electrochemical studies show that the Bodipy and porphyrin chromophores interact weakly in the ground state. However, steady-state emission and excitation spectra at room temperature reveal that fluorescence from both the Bodipy and the porphyrin of <b>3</b> are strongly quenched suggesting that, in the excited state, energy and/or electron transfer might occur. Indeed, as transient absorption experiments show, selective excitation of Bodipy in <b>3</b> results in a rapid decay (τ ≈ 2 ps) of the Bodipy-based singlet excited state and a concomitant rise of a charge-separated state evolving from the porphyrin-based singlet excited state. In contrast, room-temperature emission studies on <b>6</b> show strong quenching of the Bodipy-based fluorescence leading to sensitized emission from the porphyrin moiety due to a transduction of the singlet excited state energy from Bodipy to the porphyrin. Emission experiments at 77 K in frozen toluene reveal that the room-temperature electron transfer pathway observed in <b>3</b> is suppressed. Instead, Bodipy excitation in <b>3</b> and <b>6</b> results in population of the first singlet excited state of the porphyrin chromophore. Subsequently, intersystem crossing leads to the porphyrin-based triplet excited state

Efficient Sensitization of Dye-Sensitized Solar Cells by Novel Triazine-Bridged Porphyrin–Porphyrin Dyads

Two novel porphyrin–porphyrin dyads, the symmetrical Zn­[Porph]–Zn­[Porph] (2) and unsymmetrical Zn­[Porph]–H2[Porph] (4), where Zn­[Porph] and H2[Porph] are the metalated and free-base forms of 5-(4-aminophenyl)-10,15,20-triphenylporphyrin, respectively, in which two porphyrin units are covalently bridged by 1,3,5-triazine, have been synthesized via the stepwise amination of cyanuric chloride. The dyads are also functionalized by a terminal carboxylic acid group of a glycine moiety attached to the triazine group. Photophysical measurements of 2 and 4 showed broaden and strengthened absorptions in their visible spectra, while electrochemistry experiments and density functional theory calculations revealed negligible interaction between the two porphyrin units in their ground states but appropriate frontier orbital energy levels for use in dye-sensitized solar cells (DSSCs). The 2- and 4-based solar cells have been fabricated and found to exhibit power conversion efficiencies (PCEs) of 3.61% and 4.46%, respectively (under an illumination intensity of 100 mW/cm2 with TiO2 films of 10 μm thickness). The higher PCE value of the 4-based DSSC, as revealed by photovoltaic measurements (J–V curves) and incident photon-to-current conversion efficiency (IPCE) spectra of the two cells, is attributed to its enhanced short-circuit current (Jsc) under illumination, high open-circuit voltage (Voc), and fill factor (FF) values. Electrochemical impedance spectra demonstrated shorter electron-transport time (τd), longer electron lifetime (τe), and high charge recombination resistance for the 4-based cell, as well as larger dye loading onto TiO2

XAFS Study of Gadolinium and Samarium Bisporphyrinate Complexes

The comparative X-ray absorption spectroscopy study of gadolinium and samarium bisporphyrinate complexes represented by the formulas GdIIIH(oep)(tpp), GdIII(oep)2, GdIIIH(tpp)2 and SmIIIH(oep)(tpp), SmIII(oep)2, SmIIIH(tpp)2 is reported. The XAFS spectra are recorded on the LURE-DCI storage ring (Orsay, France) in transmission mode on the microcrystalline samples at the Gd and Sm L3 edges. The local environment for Ln3+ ions has been reconstructed applying one-shell and two-shell XAFS analysis procedures. The protonated and nonprotonated bisporphyrinate complexes present different XAFS features. After our analysis on the title derivatives, the gadolinium ion (at 80 K) is found to be bonded:  (i) to eight nitrogen atoms at R(Gd−N) 2.50 Å, for GdIII(oep)2 [Debye−Waller (DW) factor 0.004 Å2]; (ii) to seven nitrogen atoms at R(Gd−N) 2.49 Å, for GdIIIH(oep)(tpp) [DW factor 0.005 Å2] and one nitrogen at long distance; and (iii) to six nitrogen atoms at R(Gd−N) 2.50 Å [DW factor 0.006 Å2] and two nitrogen atoms at long distance for GdIIIH(tpp)2. A similar coordination sphere has been detected for the corresponding Sm derivatives. So, the samarium ion (at room temperature) is bonded:  (i) to eight nitrogen atoms at R(Sm−N) 2.53 Å, for SmIII(oep)2 [DW factor 0.006 Å2]; (ii) to seven nitrogen atoms at R(Sm−N) 2.53 Å, for SmIIIH(oep)(tpp) [DW factor 0.006 Å2] and one nitrogen at long distance; and (iii) to six nitrogen atoms at R(Sm−N) 2.50 Å, for SmIIIH(tpp)2 [DW factor 0.006 Å2] and two nitrogen atoms at long distance. As far as concerns LnIII(oep)2 complexes, the increase of Ln−N distance in the series Gd3+ 3+ < Sm3+ reflects an increase in the ionic radii, which are in good agreement with previously published XRD data on EuIII(oep)2. Moreover, the protonated LnIIIH(oep)(tpp) and LnIIIH(tpp)2 complexes possess systematically shorter distances of about 0.02 Å between the XAFS and XRD data. This difference is attributed to the asymmetry of the distribution concerning Ln−N distances