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An automated phosphoramidite method is used to synthesize and incorporate into locked nucleic acid (LNA) oligonucleotides the second generation 2'-O,4'-C-methylene-linked nucleotides. These contain hypoxanthine, 2,6-diaminopurine and 2-aminopurine nucleobases that have unique properties to further strengthen LNA technology.

Porphyrin building blocks bearing 1-4 swallowtail groups were obtained by studying synthetic routes. The swallowtail substituents do not alter the electronic or photophysical properties of the porphyrins, making them apt as building blocks for constructing large arrays for detailed physicochemical studies.

A set of hydroporphyrins, which consists of chlorin-chlorin and oxochlorin-oxochlorin are prepared with components in the same or different metalation states and studied using static and time-resolved absorption and emission spectroscopy, resonance Raman spectroscopy and electrochemical techniques. Further, a comparison between the excited-state energy transfer in arrays of hydroporphyrins and porphyrins is conducted.

A new perylene-oxochlorin dyad is synthesized and characterized for potential use in light-harvesting applications. The findings are consistent with the expectation that all charge-separated states such as perylene-monoimide (PMI)(super -1) ZnO(super +) lie energetically above both PMI and ZnO in both polar and nonpolar media.

In this study, a perylene-bis(imide)-oxochlorin dyad is synthesized to identify charge-injection or molecular-switching motifs for use in molecular photonics. Each dyad is studied in both polar and nonpolar media using static and time-resolved optical spectroscopy and electrochemical techniques.

Research has been conducted on the C-alkylated zinc chlorins. The two-step conversion of these compounds to zinc oxochlorins with the keto group located in the macrocycle's reduced ring has been carried out and the details are described.

Attempts made to investigate the self-motion of a camphor grain on a linear water route are presented. The essential features of the self-motion were reproduced by numerical calculations in relation to the spatial distribution of the camphor layer at the air-water interface.

Efforts made to study the mechanism of gating in linear versus branched multiporphyrin arrays, static and time-resolved optical spectroscopy is used. The results show the photophysics of gating and afford great flexibility and control in the design of more elaborate arrays for molecular photonics applications.

The cationic states of the lanthanide porphyrin-phthalocyanine triple-decker sandwich molecules are exceptionally attractive for molecular information storage applications. Triple-decker building blocks bearing ethyne, iodo, or iodo and ethyne groups can be prepared in a straightforward manner.

A study concerning the synthesis of porphyrins covalently linked to a phthalocyanine is presented. The cyclotetramerization of an ethyne-linked porphyrine-phthalonitrile in 1-pentanol is described.

The very low-frequency modes of the dimer of bacteriochlorophylls (BChl) which are strongly coupled to the P electronic transition initiating primary charge separation process in bacterial photosynthetic reaction centers (RC) are identified. The low-frequency, near-infrared-excitation resonance Raman spectra of RCs from Rhodobacter sphaeroides, where BChl and bacteriopheophytin cofactors are labeled with 15N or 26Mg, are analyzed, Results indicate that the strongly coupled modes involve motions limited on pyrrole ring I and the macrocycle core.

The application of the different thallium hyperfine clocks in determining the rate of hole transfer exhibited by the oxidized porphyrin dyads is discussed.

The hyperfine-clock strategy is applied to dyads of dihydroporphyrins (chlorins) and a de novo synthetic strategy is used to introduce a [super 13]C label at the 19-position of the chlorin macrocycle. The analysis of the chlorin and phorphyrin dyads has provided insights into the structural features that affect the hole/electron-transfer process.

A new rational route is developed for preparing 8,9-dibromou1-formyldipyrromethane that lead to In[Cl.sub.3]-catalyzed condensation of 4-bromo-2-(hydroxymethyl)pyrrole and prrole to give the 8-bromodipyrromethane, 1-formylation and 9-bromination. The photophysical and redox properties of the 13-substituted chlorines are compared with those of isomeric 12-substituted chlorines, which are prepared via a 7,9-dibromo-1-formyldipyrromethane.

The ground-state hole-transfer processes are studied in a series of oxidized porphyrin triads (ZnZnFb) in order to determine the rates between the nominally equivalent sites (Zn/Zn). The rate constants obtained from the analysis have helped in the design of molecular constructs for a variety of solar-energy applications.

A p-diphenylethyne-linked zinc porphyrin dyad with two [super 13]C atoms and one unlabeled was prepared to understand ground-state hole/electron-transfer process in oxidized multiporphyrin architectures. The slower hole-transfer rate compared to that of meso-diphenylethyne-linked, electron-rich porphyrin dyads is attributed to the [a.sub.2u] HOMO with substantial electron/spin density at the meso-carbons.

The investigation of the ground-state electronic communication in diphenylethyne-linked zinc-porphyrin dyads was observed to be fast on the time scale of the [super 13]C hyperfine clock.

A set of porphyrin-porphyrin and oxochlorin-oxochlorin dyads are prepared in which the constituent pigments are joined at the meso-proteins by the phenylethyne linker. The results shown and observed are useful in the design of multi pigment architectures that absorb in the red and undergo fast and efficient energy transfer, as required for light-harvesting applications.

Research has been conducted on zinc porphyrins connected via intervening bis(dipyrrinato)metal complex. The authors describe the synthesis and characterization of triads composed of zinc porphyrins' linear array.

Research has been conducted on multiporphyrin arrays. The authors describe the synthesis of these arrays carried out via the prepared and characterized dyads composed of both zinc and free-base porphyrins connected by imine-based linker.

Three sets of tetrapyrrole-chromophore arrays have been examined that exhibit panchromatic absorption across large portions of the near-ultraviolet (NUV) to nearinfrared (NIR) spectrum along with favorable excited-state properties for use in solar-energy conversion. The arrays vary the tetrapyrrole (porphyrin, chlorin, bacteriochlorin), chromophore (boron-dipyrrin, perylene, terrylene), and attachment sites (meso-position, β-pyrrole position). In all, seven dyads, one triad, and nine benchmarks in toluene and benzonitrile were studied using steady-state and time-resolved absorption and fluorescence spectroscopy. The results were analyzed with the aid of density functional theory (DFT) and time-dependent DFT calculations. Natural transition orbitals (NTOs) were constructed to assess the net change in electron density associated with each NUV-NIR absorption transition. The porphyrin- perylene dyad P-PMI displays the most even spectral coverage from 400 to 700 nm, with an average ε ∼ 43 000 M-1 cm-1. A significant contributor is a chromophore-induced reduction in the configuration interaction involving the four frontier molecular orbitals of benchmark porphyrins and associated constructive/destructive transition-dipole interference that results in intense (ε ∼ 400 000 M-1 cm-1) NUV and weak (<20 000 M-1 cm-1) visible features. P-PMI has an S1 lifetime (τs) of 4.7 ns in toluene and 1.3 ns in benzonitrile. Bacteriochlorin analogue BC-PMI has more extended spectral coverage (350-750 nm) and τs = 2.8 ns in toluene and 30 ps in benzonitrile. Terrylene analogue P-TMI has intermediate optical characteristics with τs = 310 ps in toluene and 150 ps in benzonitrile. The NTOs for most arrays show that S0 → S1 primarily involves the tetrapyrrole, but for PTMI the NTOs have electron density delocalized over the two units as a result of extensive orbital mixing. Collectively, the insights obtained should aid the design of tetrapyrrole-based architectures for panchromatic light-harvesting systems for solarenergy conversion. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the differential binding of iron(III) and zinc(II) protoporphyrin IX to synthetic four-helix bundles. The objective of the study was to create simple synthetic protein-based structures using insights drawn from nature, which are capable of assembling. Another objective was to construct molecular maquettes, which are functionalized synthetic protein versions of their biological counterparts. Results demonstrate that Zn(II)-PP binds to the synthetic proteins via single histidine axial ligation and that the binding affinity is remarkably high.

Qy-excitation Resonance Raman (RR) studies on bacterial reaction centers observed under fluorescence-free conditions allowed selective interrogation of the bacteriochlorophyll, which serves as the main electron donor, and BPhs. A RR spectroscopy technique is also used for investigating photosynthetic proteins because of the information provided by the resonance-enhanced vibrational bands on photophysically active chromophores.

Vibroniccharacteristics and spin-density distributions in thecore bacteriochlorin macrocycle were revealed by spectroscopic andtheoretical studies of 16 isotopologues. The vibrational modes incopper bacteriochlorin isotopologues were examined via resonance Ramanand Fourier-transform infrared spectroscopy. The resonance Raman spectraexhibit an exceptional sparcity of vibronically active modes of thecore macrocycle, in contrast with the rich spectra of the naturalbacteriochlorophylls. The Qy-excitationresonance Raman spectrum is dominated by a single mode at 727 cm–1, which calculations suggest is due to a symmetricalaccordion-like deformation of the five-atom Cm(CaNCa)pyrroleCmportion of the ringcore. This deformation also dominates the vibronic features in theabsorption and fluorescence spectra. The spin-density distributionsin the π-cation radical of the zinc bacteriochlorin isotopologueswere studied by electron paramagnetic resonance spectroscopy. Thespectra indicate a significant electron/spin density (ρ ∼0.1) on each meso-carbon atom. This observation contradictsthe predictions of early calculations that have been assumed to becorrect for nearly four decades. Collectively, these findings haveimplications for how the structural features that characterize naturalbacteriochlorophylls might influence energy- and electron-transferprocesses in photosynthesis and alter the thinking on the design ofsynthetic, bacteriochlorin-based arrays for solar-energy conversion. [ABSTRACT FROM AUTHOR]

A shape-persistent cyclic hexameric architecture (cyclo-Zn3Fb3U-p/m) has been prepared that is composed of three free base (Fb) porphyrins and three zinc porphyrins linked at the meso-positions via diphenylethyne unit, to study new architectures for molecular photonics applications. Findings showed that the site of attachment of the porphyrin to the linker may be employed to direct energy and/or hole/electron flow in a regulated manner among porphyrins in diverse three-dimensional architectures.

Understanding electronic communication among interacting Constituents of multicomponent molecular architectures is important for rational design in diverse fields including artificial photoayntheais and molecular electronics. One strategy for examining ground-state hole/electron transfer in an oxidized tetrapyrrolic array relies on analysis of the hyperfine interactions observed in the EPR spectrum of the π-cation radical. This strategy has been previously employed to probe the hole/electron-transfer process in oxidized multiporphyrin arrays of normal isotopic composition, wherein ¹H and 14N serve as the hyperfine "clocks", and in arrays containing site-specific 13C-Iabels, which serve as additional hyperfine clocks. Herein, the hyperfine-clock strategy is applied to dyads of dihydroporphyrins (chlorins). Chlorins are more closely related structurally to chlorophylla than are porphyrins. A de novo synthetic strategy has been employed to introduce a 13C label at the 19-position of the chlorin macrocycle, which is a site of large electron/hole density and is accessible synthetically beginning with 13C-nitromethane. The resulting singly 13C-labeled chlorin was coupled with an unlabeled chlorin to give a dyad wherein a diphenylethyne linker spans the 10-positions of the two zinc chlorins. EPR studies of the monocations of both the natural abundance and 13C-labeled zinc chlorin dyads and benchmark zinc chlorin monomers reveal that the time scale for hole/electron transfer is in the 4-7 ns range, which is 5-10-fold longer than that in analogous porphyrin arrays. The slower hole/electron transfer rate observed for the chlorin versus porphyrin dyads is attributed to the fact that the HOMO is a1u-like for the chlorins versus a2u-like for the porphyrins; the a2u-like orbital exhibits little (or no) electron/hole density at the site of linker attachment whereas the a2u-like orbital exhibits significant electron/hole density at this Site. Collectively, the studies of the chlorin and porphyrin dyads provide insights into the structural features that influence the hole/electron-transfer process. [ABSTRACT FROM AUTHOR]

Examines the synthesis of star-shaped light-harvesting arrays comprised of porphyrins and phthalocyanine core. Cyclotetramerization of substituted phthalonitriles; Isolation of arrays by chromatography; Absorption properties; Efficacy of excited-state energy transfer; Indication of ground-state electronic communication among porphyrins.

Panchromatic absorbers have potential applications in molecular-based energy-conversion schemes. A prior porphyrin-perylene dyad ( P-PMI , where "MI" denotes monoimide) coupled via an ethyne linker exhibits panchromatic absorption (350-700 nm) and a tetrapyrrole-like lowest singlet excited state with a relatively long singlet excited-state lifetime (τ S ) and increased fluorescence quantum yield (Φ f ) versus the parent porphyrin. To explore the extension of panchromaticity to longer wavelengths, three arrays have been synthesized: a chlorin-terrylene dyad ( C-TMI ), a bacteriochlorin-terrylene dyad ( B-TMI ), and a perylene-porphyrin-terrylene triad ( PMI-P-TMI ), where the terrylene, a π-extended homologue of perylene, is attached via an ethyne linker. Characterization of the spectra (absorption and fluorescence), excited-state properties (lifetime, yields, and rate constants of decay pathways), and molecular-orbital characteristics reveals unexpected subtleties. The wavelength of the red-region absorption band increases in the order C-TMI (705 nm) < PMI-P-TMI (749 nm) < B-TMI (774 nm), yet each array exhibits diminished Φ f and shortened τ S values. The PMI-P-TMI triad in toluene exhibits Φ f = 0.038 and τ S = 139 ps versus the all-perylene triad ( PMI-P-PMI ) for which Φ f = 0.26 and τ S = 2000 ps. The results highlight design constraints for auxiliary pigments with tetrapyrroles to achieve panchromatic absorption with retention of viable excited-state properties.

Six zinc(II) porphyrins bearing 0-4 meso -phenyl substituents have been examined spectroscopically and theoretically. Comparisons with previously examined free base analogues afford a deep understanding of the electronic and photophysical effects of systematic addition of phenyl groups in porphyrins containing a central zinc(II) ion versus two hydrogen atoms. Trends in the wavelengths and relative intensities of the absorption bands are generally consistent with predictions from time-dependent density functional theory calculations and simulations from Gouterman's four-orbital model. These trends derive from a preferential effect of the meso -phenyl groups to raise the energy of the highest occupied molecular orbital. The calculations reveal additional insights, such as a progressive increase in oscillator strength in the violet-red (B-Q) absorption manifold with increasing number of phenyls. Progressive addition of 0-4 phenyl substituents to the zinc porphyrins in O 2 -free toluene engenders a reduction in the measured lifetime of the lowest singlet excited state (2.5-2.1 ns), an increase in the S 1 → S 0 fluorescence yield (0.022-0.030), a decrease in the yield of S 1 → T 1 intersystem crossing (0.93-0.88), and an increase in the yield of S 1 → S 0 internal conversion (0.048-0.090). The derived rate constants for S 1 decay reveal significant differences in the photophysical properties of the zinc chelates versus free base forms. The unexpected finding of a larger rate constant for internal conversion for zinc chelates versus free bases is particularly exemplary. Collectively, the findings afford fundamental insights into the photophysical properties and electronic structure of meso -phenylporphyrins, which are widely used as benchmarks for tetrapyrrole-based architectures in solar energy and life sciences research.