Long-Chain Tetraphenylporphyrin Research Articles

SEM–EDS probing of morphological and physiological changes produced by a porphyrin photosensitizer in Psammobatis extenta electrocytes

Morphological and physiological changes produced by the intracellular localization of an alkyl long-chain tetraphenylporphyrin photosensitizer in Psammobatis extenta electrocytes were studied by means of SEM–EDS. Immediately after photosensitizer penetration, electrocytes swell and their convex faces lose all invaginations. This effect is due to chloride and sodium ion flux into electrocytes, in accordance with energy dispersive X-ray microanalysis.

Photoconductivity of Discotic Liquid Crystals: a Mesogenic Long-Chain Tetraphenylporphyrin and Its Metal Complexes

A mesogenic long-chain tetraphenylporphyrin and its metal complexes(Ni(II), V˭O(IV) and Si(OH)2) were studied on the mesomorphism and photoconductivity in a symmetrical sandwich-type ITO cell. These complexes show so-called “lamellar-type” mesophases having a layered structure like smectic mesophase. The photocurrent behaviour of these compounds were compared to clarify the characteristic properties of photoconductivity for lamellar mesophases.

Photoconductive Properties of a Mesogenic Long-Chain Tetraphenylporphyrin Oxovanadium(IV) Complex in a Symmetrical Sandwich-Type ITO Cell

The photoconductive properties of 5,10,15,20-tetrakis(4-n-pentadecyl-phenyl)porphinatooxovanadium(IV) was investigated to be compared with those of the free base compound for a symmetrical sandwich-type ITO cell. The similar photocurrent rectification behavior to the free base tetraphenylporphyrin mesogen was shown. However, the observed photocurrent remarkably larger than that of the free base compound for all phases. The temperature dependence of the dark- and photo-currents were also investigated.

Photoconductive properties of a mesogenic long-chain tetraphenylporphyrin oxovanadium(IV) complex

The photoconductive properties of a mesogenic long-chain tetraphenylporphyrin, 5,10,15,20-tetrakis(4- n-pentadecylphenyl)porphinatooxovanadium(IV) were investigated and compared with those of the metal-free compound for a symmetrical sandwich-type ITO cell. This compound shows two types of lamellar mesophases (M LC and M L phases) and the phase transition sequence is Cr 51 M LC 83 M L 140 Iso. A similar photocurrent rectification behavior to the corresponding metal-free tetraphenylporphyrin mesogen was shown. However, the observed photocurrent was remarkably larger than that of the metal-free compound for all phases. The action spectra and the temperature dependence of the dark- and photocurrents were also investigated on the mesomorphic phase transition behavior. These results imply that the photoconductive property of mesogenic tetraphenylporphyrin-based compounds could be drastically affected by a change of molecular fluctuation and long-range order through mesomorphic phase transitions and a metal species inserted in the central core.

Mesomorphic and photoconductive properties of a mesogenic long-chain tetraphenylporphyrin nickel(ii) complex

A tetraphenylporphinatonickel-based mesogenic compound 5,10,15,20-tetrakis(4-n-pentadecylphenyl)porphinatonickel(II) (C15TPPNi) was synthesised and its mesomorphic and photoconductive properties were investigated. The photoconductive properties were compared with those of the metal-free compound. All measurements were carried out for symmetrical ITO/C15TPPNi/ITO type cells and steady-state currents in the constant temperature conditions were detected. A photocurrent rectification was seen in either the crystal phase or lamellar mesophase of C15TPPNi. The metal-free compound with pentadecyl chains showed a strong dependence of photocurrent rectification on mesomorphic phases: the rectification is shown in the cell of crystal and low-temperature lamellar phases and it disappears in the high-temperature lamellar mesophase. This phenomenon was interpreted in terms of the various mechanisms of charged carrier generation with the phase transition, based on the results of the action spectra and the illumination light intensity dependence of the photocurrent. The improvement of the contact for electric conduction at the interface upon heating was found, which is a special feature of this mesomorphic phase in the ITO/C15TPPNi/ITO cell in comparison with the metal-free compound.

Photocurrent Action Spectra of the Photoconductive Cell with a Mesogenic Long-Chain Tetraphenylporphyrin

Photocurrent action spectra for the cell in which 5,10,15,20-tetrakis(4-n-pentadecylphe-nyl)porphyrin (C15TPPH2) is sandwiched by ITO electrodes were measured and the phase dependence of the action spectra indicated a variable combination of the extrinsic and intrinsic carrier generation processes on the mesomorphic phase transitions. This results is in agreement with that deduced by the illumination intensity dependence of photocurrent.

Photoconductivity of Discotic Liquid Crystals Derived from A Long-Chain Tetraphenylporphyrin

ABSTRACTPhotoconductivity of a mesogenic tetraphenylporphyrin (TPP) is shown in relation to the mesomorphic phase transition behavior. The TPP mesogen shows two types of mesophases having smectic-like order (lamellar mesophases : DL and DLC phases named in this work) and the photocurrent changes stepwise at the phase transitions with non-Arrhenius dependence whilst the darkcurrent tends to be Arrhenius. The hole mobility was measured for the random domain cell and was found to be faster than 10−4 cm2v−1sec−1 in the mesophases. The cell used for the photocurrent measurements was a sandwich-type one using two ITO glass slides as electrtodes and show rectification behavior for the crystal and the low-temperature mesophase (DLC) in contrast to non-rectification of photocurrent in the high-temperature mesophase (DL). These properties of charge carrier migration as an electronic process are profoundly related to molecular order as well as molecular motions in mesophase.

Mesomorphic Properties of a Long-Chain Tetraphenylporphyrin Oxomolybdenum (V) : Complex. Effect of the Axial Ligands on the Mesomorphic Properties.

Mesomorphic Properties of a Long-Chain Tetraphenylporphyrin Oxomolybdenum (V) : Complex. Effect of the Axial Ligands on the Mesomorphic Properties.

Photoconduction of a mesogenic long-chain tetraphenylporphyrin in a symmetrical sandwich-type cell

Photoconductive properties of a mesogenic long-chain tetraphenylporphyrin (C15TPPH2) were investigated for a symmetrical sandwich-type (ITO/C15TPPH2/ITO) cell. The action spectra and illumination light intensity dependence of the steady state photocurrent indicated that both extrinsic and intrinsic processes of photocarrier generation contribute to the apparent photocurrent behavior which is variant on the mesomorphic phase transitions. In particular, it was inferred that the mesomorphic phase transition from the low- to high-temperature lamellar mesophases leading to the sudden disappearance of photocurrent rectification behavior, depress the extrinsic process of charge carrier generation. These results strongly imply that the photoconductive property of mesogenic materials could be drastically affected by a change of the molecular fluctuation and long-range order through mesomorphic phase transitions.