Cavity effect amplification in the recognition of dicarboxylic acids by initial ditopic H-bond formation followed by kinetic trapping

Spectroscopic study on enantiomeric Ni(II) complexes of porphyrin-porphyrin Tröger's base and porphyrin-chlorin spiro-Tröger's base derivatives supported by DFT calculations

The chiral properties of nickel(II) complexes of porphyrin-porphyrin Tröger's base and porphyrin-chlorin spiro-Tröger's base with phenyl or 3-methoxyphenyl substitutions in their meso-positions were studied. Enantioseparation of racemic mixtures was investigated via high-performance liquid chromatography (HPLC) on an analytical ReproSil Chiral-NR column. The optimal conditions were utilized for a multimilligram scale isolation with a semipreparative column. The purity of the isolated enantiomers was determined by HPLC and UV-Vis spectroscopy. The absolute configurations of the isolated enantiomers were determined by evaluating the Cotton effect in electronic circular dichroism spectra. The determination was supported by TDDFT calculations, in which good agreement was achieved between the experimental and simulated spectra. The maximum molar ellipticity values, [θ]λmax given in deg ∙ cm2 ∙ dmol-1, were [θ]435 = 1.73 ∙ 107 for phenyl spiroTB and [θ]436 = 1.24 ∙ 107 and [θ]436 = 2.15 ∙ 107 for 3-methoxyphenyl TB and spiroTB, respectively.

Electrochemically Switchable Molecular-Tweezers

Synthetic receptors possessing two complexing chromophores connected by a single spacer are referred to as molecular tweezers. We report an electrochemically triggered molecular tweezers, which is a calix[4]arene-bis-porphyrin conjugate, that acts as a proof-of-concept demonstration system showing an electro-statically induced approach to guest release. The electrochemical behavior represents that 1,4-diazabicyclo[2.2.2]octane (DABCO) is released from the complex formed between calix[4]arene-bis-porphyrin conjugate and DABCO, just after cooperative two-oxidation occurs at 0.41 V.

Synthetically tuneable biomimetic artificial photosynthetic reaction centres that closely resemble the natural system in purple bacteria

Porphyrin-based photosynthetic reaction centre (PRC) mimics, ZnPQ-Q2HP-C60 and MP2Q-Q2HP-C60 (M = Zn or 2H), designed to have a similar special-pair electron donor and similar charge-separation distances, redox processes and photochemical reaction rates to those in the natural PRC from purple bacteria, have been synthesised and extensive photochemical studies performed. Mechanisms of electron-transfer reactions are fully investigated using femtosecond and nanosecond transient absorption spectroscopy. In benzonitrile, all models show picosecond-timescale charge-separations and the final singlet charge-separations with the microsecond-timescale. The established lifetimes are long compared to other processes in organic solar cells or other organic light harvesting systems. These rigid, synthetically flexible molecules provide the closest mimics to the natural PRC so far synthesised and present a future direction for the design of light harvesters with controllable absorption, redox, and kinetics properties.

Photophysical characterisation of Tröger's base molecular scaffolds: a combined theoretical and experimental study

The photophysics of Tröger's base in the ground and excited states was performed by comparing experimental and theoretical properties predicted using TD-DFT calculations.

Formation of a hybrid compound composed of a saddle-distorted Tin(IV)-porphyrin and a Keggin-type heteropolyoxometalate to undergo intramolecular photoinduced electron transfer

Nonplanar Sn(IV)-porphyrin complexes, [Sn(TMPP(Ph)(8))-Cl(2)] (1) and [Sn(TMPP(Ph)(8))(OMe)(2)] (2) (TMPP(Ph)(8): 5,10,15,20-tetrakis(4-methoxyphenyl)-2,3,7,8,12,13,17,18-octaphenylporphyrinato), were prepared and characterized by spectroscopic and electrochemical methods together with X-ray crystallography. Variable-temperature (1)H NMR study revealed that the coordination of the methoxo ligand of 2 is weak enough in solution to enhance the axial ligand exchange with a Keggin-type phosphotungstate (α-[PW(12)O(40)](3-)) due to the steric stress between the axial methoxo ligand and the peripheral phenyl groups of the porphyrin ligand. The formation of a novel 1:1 donor-acceptor complex, [Sn(TMPP(Ph)(8))(OMe)(α-[PW(12)O(40)])](2-) (4) was confirmed by (1)H NMR and UV-vis spectral titrations, and also by MALDI-TOF-MS measurements. Electrochemical measurements for the donor-acceptor complex in PhCN revealed that the Sn(IV)-TMPP(Ph)(8) moiety acts as an electron donor and the α-[PW(12)O(40)](3-) moiety acts as an electron acceptor and that the energy level of the electron-transfer (ET) state of the 1:1 complex (1.17 eV) is lower than that of the triplet excited states of the SnTMPP(Ph)(8) complex (1.31 eV). Femtosecond and nanosecond laser flash photolysis measurements indicate that intersystem crossing from the singlet excited sate to the triplet excited state occurs followed by intramolecular photoinduced electron transfer from the triplet excited state of the Sn(IV)-TMPP(Ph)(8) moiety to the α-[PW(12)O(40)](3-) moiety in the 1:1 complex in benzonitrile.

Complete 1H and 119Sn NMR spectral assignment for an asymmetric di[dihydroxotin(IV)] bis-porphyrin supramolecular host and its corresponding tetraacetato complex

The full (1)H and (119)Sn NMR spectral assignments for a di[dihydroxotin(IV)] bis-porphyrin supramolecular host I and for the di[diacetatotin(IV)] complex II are presented. Despite the lack of varied chemical functionality in these molecules, all of their 64 proton environments are non-equivalent. This is due to the asymmetry afforded by the Tröger's base (methanodiazocine) bridge between the porphyrin and quinoxalinoporphyrin macrocycles. The methanodiazocine bridge imparts chirality and concavity on the host framework and the quinoxalino link to one porphyrin macrocycle results in a negation of C(2) symmetry. The anisotropy of the aromatic porphyrin and quinoxalinoporphyrin macrocycles results in good dispersion for all 60 signals of the host framework and for the four ligands bound in the axial positions of the tin(IV) centres. The full assignment of the (1)H NMR spectra for these systems was achieved using dqf-COSY, NOESY, ROESY, (1)H-(119)Sn HMQC, (1)H-(13)C HSQC and (1)H-(13)C HMBC spectroscopy at temperatures that optimised dispersion. The (1)H-(119)Sn HMQC was particularly useful in this assignment. The (119)Sn chemical shift is sensitive to the functionality of the porphyrin and to the nature of the axial ligation, and the (119)Sn centre couples to both the ligand protons and the beta-pyrrolic protons. This allows unequivocal identification of the spin systems associated with each metal centre.