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An investigation into the highly efficient energy migration processes occurring in natural light harvesting apparatuses was carried out by synthesizing covalently linked cyclic porphyrin arrays. The results showed that there is efficient energy migration within the cyclic porphyrin arrays at the single molecule level.

A photoactive layer, consisting of electron-donating zinc prophyrin and electron-accepting fullerene arrays on the dendrimer surface is constructed using [DP.sub.m] 9m= 6, 12, and 24) and Py2[F.sub.n] (n= 1-3) by means of a multivalent surface ligation of dendritic macromolecules. Upon increment of the numbers of these donor and acceptor units, the electron transfer reaction was remarkably facilitated, while the recombination of the resulting charge-separated state remained virtually intact.

The photophysics of a series of bis-metal doubly N-confused hexaphyrins (1.1.1.1.1.1) was investigated using various fluorescent techniques and geometry-optimized ab inito calculations. Bis-Zn(II) and free-base doubly N-confused hexaphyrins show [pi]-[pi*] transitions around a hexaphyrin ring at the B3LYP/6-3IG level and the absorption spectra of bis-Cu(II) and bis-Co(II) doubly N-confused hexaphyrins are relatively broad due to large couplings between the metal d-orbitals and [pi]-electrons of the hexaphyrin rings.

Conformational hetereogenties for the orthogonal porphyrin arrays is investigated by both ensemble and single molecule spectroscopy as the number of porphyrin molecules in the array increases. The fluorescence properties of porphyrin arrays on single molecule level will provide a platform for further applications as molecular photonic wires.

The eletronic natures of representative expanded porphyrins, [26]- and [28]hexaphrins is explored to investigate the interplay between the aromaticity and antiaromaticity that is brought by two electron oxidation/reduction processes. The enhanced excited-state lifetimes for various hexaphyrins go in line with the increased two-photon absorption cross-section values and the ring planarity.

The overall excitation energy relaxation dynamics in linear porphyrin arrays and the energy transport phenomena by attaching an energy acceptor to one end of a linear porphyrin array by using steady state and time-resolved spectroscopic measurements are investigated. It is revealed that the solvation dynamics and conformational dynamics contribute significantly to the energy relaxation processes of linear porphyrin arrays.

An investigation on the excited state dynamics and two-photon absorption properties of four novel linked porphyrin dimers in toluene is presented. The results indicate that the fused porphyrin dimers exhibit extremely increased two-photon absorption cross-section values (12000-15000 GM) porphyrin monomers owing to much enhanced pi-electron delocalization throughout the porphyrin dimers ring.

The various photophysical properties of the three-dimensional zinc(II) prophyrin box and its constituent unit are investigated. The relationship between molecular structures in three-dimensional molecular networks and exciton coupling/transport processes is shown.

Binuclear complexes with cyclometalated ends of the [Ru((bpy)(sub 2))(ppH)](super +) type (bpy=2,2'-bipyridine, ppH=2-phenylpyridine), linked by various spacers are prepared. The results could be rationalized by theoretical calculations at the extended Huckel level.

A new biological approach to fabricate Au nanowires is examined by using sequenced peptide nanotubes as templates. The sequenced histidien-rich peptide molecules were assembled on nanotubes, and the biological recognition of the sequenced peptide selectively trapped Au ions for the nucleation of Au nanocrystals.

A broad class of molecular catalysts is developed that have temperature-dependent solubilities, such that they could be applied under homogeneous conditions at elevated temperatures and efficiently recovered by simple liquid/solid phase separations at lower temperatures. The evolution of a new general method for catalyst recovery is predicted-fluorous catalysis without fluorous solvents.

Femtosecond fluorescence anisotropy measurements for a variety of cyclic porphyrin arrays are reported. Anisotropy decay times of the porphyrin arrays could be well described by the Forster incoherent excitation hopping process between the porphyrin units.

The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The overall relaxation dynamics of the porphyrin tapes show a systematic change as the number of porphyrin pigments increase in the array

Femtosecond time-resolved emission as well as transient absorption spectroscopy of pi-conjugated polymeric thin film reveals an apparent induction time for the appearance of spectrally narrowed emission (SNE) in contrast with an instantaneous buildup of normal emission. The study on ultrafast intensity-dependent spectroscopies demonstrate that the origin of SNE phenomena in pi-conjugated polymer is amplified spontaneous emission (ASE), which induces prompt and efficient depopulation of singlet excitons.

The light emission decay in bare gold particles by using the fluorescence up-conversion technique is reported. The results indicate that a weak light emission from relatively large gold nanoparticles is attributable to the interactions between surface plasmons and incident photons that occur simultaneously with the thermal electron relaxation.

The photoinduced energy transfer processes in 1,4-phenylene, 1,3-phenylene, 1,2-phenylene, and 4,4'-bi-phenylene-linked and directly-linked zinc(II) free-base porphyrins heterodimers in THF were investigated by femtosecond transient absorption spectroscopy. The results indicate that even for the covalently-linked models the relative contribution of the through-space Coulombic interaction becomes increasingly important upon the decrease of the center-to-center separation.

The photochemical synthesis of the benzonaphthyridinones from the 2-halo-N-pyridinylbenzamide photoreaction has been conducted. The reaction mechanism based on the preparative, kinetic and laser flash photolysis studies is discussed.

Time-resolved fluorescence and transient absorption techniques are used to investigate the energy relaxation dynamics of the photoexcited [2+2]-bridged C60 dimer in 0-dichlorobenzene. The absorption and fluorescence spectra of the C60 dimer show that the monomeric moieties of C60 are only weakly interacting with each other, which indicates that the C60 dimer can be considered as a nearly decoupled bichromophoric molecular system in the ground state.

Experiments were performed to determine the mechanism for the photocyclization of halopyridinium salt attached to arene. The transient species involved in the laser flash photolysis of the halopyridinium salts and the reactions of the steady-state photoreaction of 2-halopyridinium salt tethered to phenyl ring were also examined. It was observed that the presence of the ethylene and methylene groups influenced the involvement of the singlet and the triplet states in photocyclization.

Nanoelectrodes are used to measure electrical conduction on two extreme types of directly linked porphyrin arrays. The stronger Pi-electron conjugation in T8, as compared with that of Z48, results in better electrical conduction.

A study was conducted to examine effect of solvent and substituent effects on the photophysical properties of a varieyt of N-fused porphyrin derivatives, where the mesityl group as the meso-positions plays a unique role. Introduction of electron-withdrawing groups such as a nitro group and a cyano group on the macrocycles caused significant refinements in their emission efficiency while intact N-fused tetraarylporphyrins showed almost no emission.

Cyanostilbene-based highly luminescent molecular sheets are described that have displayed two-color fluorescence switching in response to pressure, temperature and solvent vapor. Multistimuli responsive system is exclusive in terms of the slip-stacking of molecular sheets and has provided a novel concept of rewritable fluorescent optical recording media.

The application of the various Suzuki-Miyaura coupling reactions for the synthesis of directly Pd(II)-bridged porphyrin belts is discussed. The remarkable curvatures and large TPA values exhibited by these complexes are also analyzed.

Isolation and characterization of a meso,meso-diketohexaphyrin as a chemically stable non-Kekul singlet biradicaloid are described. The findings for two unpaired electrons which are seemingly delocalized on two tripyrrolic units separated by C=O bonds underscore the potential of expanded porphyrins to achieve unique electronic states.

The relationship between conformational behaviors and electronic structures of [pi]-stacked perylenediimides (PDIs) is understood by examining the changes in the excimer-like state of cofacial PDI oligomers that have resulted from [pi]-stacking in real time by monitoring the single-molecule fluorescence intensity and lifetime trajectories in a PMMA polymer matrix. The fluorescence intensity and lifetime of [pi]-stacked perylenediimides are sensitive to the degree of [pi]-orbital interactions among PDI units, which is associated with molecular conformations in the polymer matrix.

Protonation-triggered conformational changes of meso-octakis(pentafluorophenyl) [36]octaphyrin and [38]octaphyrin are examined. The absorption/fluorescence, excited singlet/triplet state lifetimes and two-photon absorption cross-section values are described for both protonated [36] and [38]octaphyrins in conjunction with their Mobius or Huckel aromaticity.

A series of zinc porphyrin arrays consisting of a meso-meso linked porphyrin dimer, a meta-phenylene linked dimer, gable-like tetramers consisting of the meso-meso linked dimers bridged by a meta-phenylene linker, and a dodecameric ring composed of the alternating dimeric pattern and intramolecular hole hopping between the porphyrin moieties are analyzed by using electron paramagnetic resonance (EPR) spectroscopy. The results have shown that hole hopping is rapid even though the meta-phenyl bridges and direct meso-meso linkages have not provided optimal electronic coupling between the porphyrins within these multiporphyrin arrays.

The electronic structures and energy relaxation dynamics of vinylene-bridged hexaphyrins are examined by using steady-state and time-resolved spectroscopies in order to disclose their aromaticity-dependent electronic and magnetic properties. The studies have provided insights into the aromaticity-driven electronic properties of various porphyrinoids as well as of aromatic/antiaromatic hydrocarbon systems.

A benzopyrane-fused [28]hexaphyrin is prepared by the simple heating of [26]hexaphyrin in acetic acid. The studies have shown that benzopyrane-fused [28]hexaphyrin is the first macrocycle that has acquired distinct Mobius aromaticity without any help from metal coordination, temperature control or protonation.

A novel strategy is developed for constructing a vertical arrangement of bicontinuous donor-acceptor arrays on a semiconducting electrode. The relationship between the film structure and the photoelectrochemical properties is analyzed as a function of the number of donor layers.

Porphyrin rings CZ4, CZ6 and CZ8 consisting of four, six, and eight porphyrins, immobilized in a thin PMMA film, are examined by using single molecule fluorescence spectroscopy with a focus on the influences of the overall structural rigidity as the ring size of porphyrin array increases. The results have highlighted CZ4 as a potential and promising candidate for application in artificial light harvesting solid-state devices.

The synthesis and characterization of meso-(4-(N,N-dibenzylamino)phenyl)-substituted subporphyrins that display unique absorption properties and enhanced fluorescence emission due to the intramolecular charge transfer (CT) interaction in the opposite direction are presented. Distinct CT interactions have led to large changes in the absorption spectra and drastic enhancement of the fluorescence intensity, which are used for analyzing new chemosensors.

The ensemble and single-molecule spectroscopy technique is employed to explain the molecular structures and photophysical properties of the zinc(II) porphyrin dendrimers with and without guest binding. The analysis reveals that the use of appropriate bidentate guests can easily help in controlling the porphyrin dendritic structures in poor environmental conditions.

The studies of two-photon absorption (TPA) phenomena of a series of single-strand as well as supramolecular self-assembled ladders and prisms of highly conjugated ethyne bridged multiporphyrin dimer, trimer, and star shaped pentamer are described. The results suggested that the TPA maximum position is determined by the [pi]-delocalization pathway and the TPA property of the pentamer arise from its basic trimer unit rather than the entire molecule.

The excited-state dynamics and the photophysical properties of the representative core-modified expanded porphyrins are discussed. The discussed complexes are shown to exhibit excellent aromaticity and enhanced ring planarity, as compared to their corresponding all-aza expanded porphyrins.

The excitation energy transfer process of meso-meso linked zinc(II) porphyrin arrays are examined by using the on-the-fly filtered propagator path integral method. The studies have shown that the coherence length is the result of electronic and environmental effect rather than the structure disorder.

Various spectroscopic techniques are employed to study the relationship between the nonlinear optical properties and aromaticity in congeneric pentapyrrolic expanded porphyrins. The compounds with high aromaticity are shown to exhibit higher two-photon absorption.

A controlled phosphorescence color tuning in a series of cyclometalated heteroleptic Ir(III) complexes containing chromophoric 2-(2-hydroxyphenyl)oxazole-derivative ancillary ligands (LX). The characteristic energy-harvesting phosphorescence is shown in electrophosphorescence devices.

A study was conducted to explore the excitation energy migration processes occurring in a series of cyclic porphyrin arrays which show structural similarity found in the L[H.sub.2] complexes in purple bacterial photosynthetic systems. The spectroscopic results obtained on the single molecules provide detailed information on the excitation energy migration efficiency in the solid state.

The first synthesis and characterization of meso-aryl-substituted subchlorins is described. Large optical and electrochemical changes have accompanied the subporphyrin-to-subchlorin structural changes, which are similar to porphyrin-to-chlorin changes.

The article presents the synthesis, STM detection and the efficient energy hopping (EEH) in near-infrared region of cyclic and hexagonal prismatic porphyrin arrays. Two-dimensional cyclic arrays are found to be excellent for EEH processes for artificial biomimic light harvesting apparatus.

Effective synthetic routes are developed for peripherally substituted bis-gold(III) hexaphyrins starting from [26]hexaphyrin(1.1.1.1.1.1). Reversible aromatic-to-antiaromatic changes of hexaphyrin bis-gold(III) complexes upon two-electron reduction and oxidation have quantified the affect of the aromaticity upon two-photon absorption (TPA) value.

Two synthetic methods of meso-aryl-substituted subporphyrins are formulated by using the reaction of pyridine-tri-N-pyrrolylborane with a series of aryl aldehydes. The analysis has shown that meso-aryl-substituted subporphyrins can be used for constructing curved [pi]-conjugated molecules such as molecular spheres, molecular tubes and molecular belts.

The synthesis of an inverted sapphyrin derivative is described where inversion of two pyrrolic nitrogen atoms is configurationally enforced. The system is the first expanded porphyrin containing a 3,3-bipyrrolic subunit and displays weak aromaticity as judged from its spectroscopic features and supporting theoretical calculations.