Youkoh Kaizu

J-aggregate formation of a water-soluble porphyrin in acidic aqueous media

J aggregate of a water‐soluble porphyrin, 5,10,15,20‐tetra(4‐sulfophenyl)porphyrin (H2TPPS44−), formed in acidified aqueous solutions, exhibits sharp and intense absorption bands at 491 and 707 nm. These characteristic transitions, J bands, are of linear oscillators polarized in the long axis of rodlike aggregate. The molecules in the aggregate stack so as to lift the degeneracy of the porphyrin planar oscillator excited states. Measurements of flow‐induced linear dichroism, circular dichroism, magnetic circular dichroism, as well as polarized fluorescence excitation spectra provide evidence not only of linear oscillator character of the intense J band at 491 nm, but also of presence of another diffuse absorption band around at 420 nm polarized in the short axis of the aggregate, which is the counterpart of the 491 nm band of porphyrin Soret origin. Extrinsic circular dichroism is induced upon addition of L‐tartaric acid or by mechanical swirling flow in the period of aggregate growth. Resonance Raman spe...

Luminescence of some metalloporphins including the complexes of the IIIb metal group

Luminescence yields and decay lifetimes were measured on some metalloporphyrins including the complexes of the IIIb metal group. The S2 emission was observed for AlClTPP (TPP: tetraphenylporphin), GaClTPP, and InClTPP as well as some other TPP metal complexes, ZnP (P:porphin) and H4P2+ (diacid), while it was not detected for H2TPP, H2OEP (OEP: octaethylporphin), AlClOEP as well as other OEP metal complexes. The rate of S2→S1 internal conversion is dependent upon the peripheral substituents rather than the central metal ion and is enhanced in the porphyrins which do not emit the S2 fluorescence. On the other hand, the intersystem crossing plays a more important part in the relaxation process of the S1 state. With increase in the atomic number of the central metal ion as well as its axial ligand, the yield and decay lifetime of the S1 emission are reduced. In the relaxation of the T1 state, the radiative decay is also accelerated for the central metal ion with higher atomic number.

HOLE DELOCALIZATION IN NAPHTHALOCYANINATOPHTHALOCYANINATOLUTETIUM(III)

Abstract From comparison of the absorption and MCD spectra of a hetero-dimer complex, naphthalocyaninatophthalocyaninatolutetium (III) ([Lu(Nc)(Pc)]), with the corresponding spectra of [Lu(Pc) 2 ] and [Lu(Nc) 2 ] (Pc=phthalocyanine, Nc=naphthalocyanine), the delocalization of the unpaired electron in [Lu(Nc)(Pc)] is demonstrated. The lowest excitations of the hetero-dimer arise in the middle of those of [Lu(Pc) 2 ] and [Lu(Nc) 2 ]. The lowest excited states of these complexes are assigned on the basis of the hole delocalization.

Study of higher excited singlet states of zinc(II)‐tetraphenylporphin

The mechanism for the production of the S2 state fluorescence following the excitation to the S1 states of zinc (II)‐tetraphenylporphin has been investigated by using two‐photon absorption and optical–optical double resonance techniques. The main process populating the S2 state is found to be a stepwise two‐photon absorption through the S1 state (the Q state) even by the excitation of relatively low power density (<5×1015 photons cm−2 pulse−1) of a nitrogen pumped dye laser. The absorption cross sections σ1n of the Sn ← S1 transition are determined from the kinetic analyses based on the two‐photon absorption measurement. The Sn ← S1 absorption spectrum obtained is structureless and its σ1n values vary from 4.74×10−16 to 1.02×10−15 cm2 molecule−1 in the wavelength region of 490–560 nm. This observation suggests that the corresponding Sn ← S1 transition possesses a strongly allowed nature and there exists a higher excited singlet state of gerade symmetry in the 17 800–20 400 cm−1 region above the ground sta...

Synthetic, spectroscopic and theoretical study of novel supramolecular structures composed of lanthanide phthalocyanine double-decker complexes

Abstract This paper reviews the authors’ attempts to create novel supramolecular structures composed of bis(phthalocyaninato)lanthanides and the analysis of their geometric and electronic structures. We synthesized tetra- and mono-crown-substituted bis(phthalocyaninato)lutetium, which show different aggregate forms under various conditions. The aggregate structures fall into three categories: (1) a D 4 h vertically stacked structure formed from the tetra-crown complex and cations such as K + or NH 4 + ; (2) a sliding form composed of tetra-crown complexes in methanol/chloroform mixed solvent; and (3) a pivoted form constructed from mono-crown substituted complexes with cations such as K + . The electronic structure of the supramolecular structures and magnetic interactions within are discussed.

The lowest excited states of copper porphyrins

Relaxation processes of excited copper porphyrins were studied with relevance to the structure of the substates of the lowest excited states. Lifetimes of luminescence at room temperature were determined as 17, 29, 69, and 105 ns for T(EtO)PPCu [T(EtO) PP: 5, 10, 15, 20‐tetra (p‐ethoxyphenyl)porphin], TPPCu(TPP: 5, 10, 15, 20‐tetraphenylporphin), TFPPCu[TFPP: 5, 10, 15, 20‐tetra(pentafluorophenyl)porphin], and OEPCu(OEP: 2, 3, 7, 8, 12, 13, 17, 18‐octaethylporphin) in toluene, respectively. Emission intensities and lifetimes of OEPCu and TFPPCu measured as a function of temperature show a variation ascribed to a Boltzmann distribution between the lowest trip–doublet and –quartet with an energy gap of 300–400 cm−1. The anomalous temperature dependence for TPPCu and T(EtO)PPCu is explained by a larger energy gap and larger vibronic distortions in the excited state. The difference in behavior is attributed to the orbital nature of the triplet: ‖2,4[b31(a1e)]〉 for OEPCu and TFPPCu but ‖2,4[b31(a2e)]〉 for TPPC...

Exciton coupling and charge resonance in the lowest excited states of lutetium phthalocyanine dimer and trimer

Abstract The measurement of the electronic spectrum of triple-decker phthalocyanine trimer in solution showing the existence of low-lying excited states in the near-IR region is reported. The spectroscopic measurement in solution was made possible by using a newly synthesized trimer ([(Pc)Lu(CRPc)Lu(Pc)]: Pc=phthalocyanine; CRPc=15-crown-5 substituted Pc) having high solubility and purifiability. The lowest excited states caused by intra- and inter-macrocyclic HOMO—LUMO transitions are studied in terms of exciton coupling and charge resonance. The inherent differences between the trimer and dimer are elucidated. The assignment of absorption bands below 20 × 10 3 cm −1 is discussed.

Biradical state in phthalocyanine (2 + 2) tetramer composed of two bis (phthalocyaninato) lutetium radicals

Abstract The behavior of two holes in a phthalocyanine (2 + 2) tetramer which consists of two bis (phthalocyaninato) lutetium radicals is studied by absorption, MCD, ESR spectra. The dimer, one of whose phthalocyanine rings is peripherally substituted by four 15-crown-5 rings, forms a (2 + 2) tetramer in the presence of K + ions in solution. All major absorption bands except the lowest energy band are blue-shifted with the tetramer formation. The (2 + 2) tetramer preserves the near-IR band that is a characteristic of the dimer radical, and shows a triplet ESR spectrum. The experimental results indicate that the tetramer is a biradical.

Axially polarized NIR absorption bands in electron‐ deficient lanthanide phthalocyanine dimers and trimers

Absorption and MCD spectra of the two-electron oxidized lutetium phthalocyanine trimer [(Pc)Lu(CRPc)Lu(Pc)]2+ (Pc ≡ phthalocyanine;CRPc ≡ 15-crown-5-substituted Pc) as well as the MCD spectrum of the oxidized lutetium Pc dimer [Lu(Pc)2]+ are reported. These ‘two-electron-deficient’ Pc stacks show absorption bands in the NIR region whose intensities are comparable with those of the Q bands. The band of [Lu(Pc)2]+ showed only an MCD B term with no A term contribution, from which we assign the band to a non-degenerate transition whose transition moments are perpendicular to the Pc planes. In both trimer and dimer cases the excitation energy is higher than that of the corresponding NIR band in the ‘one-electron-deficient’ Pc stack [(Pc)Lu(CRPc)Lu(Pc)]+ or [Lu(Pc)2], but the magnitudes of the shift were significantly different (1500 cm−1 in the trimer and 4500 cm−1 in the dimer). The energy shifts are shown to be represented by a pair of two-electron repulsion integrals in a localized orbital basis. The model reproduced well the direction and magnitude of the shifts using numerical values of the integrals.

An electrostatic approach to the structure of hydrated lanthanoid ions. [M(OH2)9]3+versus[M(OH2)8]3+

The bond energies of ennea- and octa-aqua-coordinated polyhedra of lanthanoid ions have been calculated on the electrostatic model. Sums of coordination bond energies and Born hydration enthalpies of the aqua complexes predict an exclusive stabilization of the enneahydrate regardless of whether the central metal ion is of the earlier or later elements of the series. However, the difference between the hydration free energies evaluated for octa- and ennea-hydrate ions shows that there is a preference to form the enneahydrate for the earlier elements, but the octahydrate is formed for the later elements. A small difference in hydration free energy results in the transitional coordination number for the elements near to gadolinium. As an application of the present model, the equilibrium constant for the 5d� 4f excited states of [Ce(OH2)8]3+ and [Ce(OH2)9]3+ in aqueous media have been calculated.