A dithienylethene (DTE)-porphyrin (P)-fullerene (C(60)) triad molecule in which intramolecular photoinduced electron transfer is controlled by the photochromic DTE moiety has been prepared. Irradiation of with visible light gives open form (DTEo). Excitation porphyrin DTEo-(1)P-C(60), undergoes a time constant 25 ps to generate DTEo-P(.+)-C(60)(.-). ultraviolet produces closed (DTEc). DTEc-P-C(60) yields DTEc-(1)P-C(60), whose first excited singlet state quenched 2.3 singlet-singlet energy...

Functional mimics of a photosynthetic antenna-reaction center complex comprising five bis(phenylethynyl)anthracene antenna moieties and porphyrin−fullerene dyad organized by central hexaphenylbenzene core have been prepared studied spectroscopically. The molecules successfully integrate singlet−singlet energy transfer photoinduced electron transfer. Energy from the antennas to porphyrin occurs on picosecond time scale with quantum yield 1.0. Comparisons model compounds theory suggest that...

In the photosynthetic photosystem II, electrons are transferred from manganese-containing oxygen evolving complex (OEC) to oxidized primary electron-donor chlorophyll P680(•+) by a proton-coupled electron transfer process involving tyrosine-histidine pair. Proton tyrosine phenolic group histidine nitrogen positions redox potential of between those and OEC. We report synthesis time-resolved spectroscopic study molecular triad that models this transfer. The consists high-potential porphyrin...

A highly efficient functional mimic of a photosynthetic antenna−reaction center complex has been designed, synthesized, and studied spectroscopically. The antenna, consisting four covalently linked zinc tetraarylporphyrins, (PZP)3−PZC, coupled to free-base porphyrin−fullerene artificial reaction center, P−C60, form (PZP)3−PZC−P−C60 hexad. As revealed by time-resolved absorption emission studies in 2-methyltetrahydrofuran solution at ambient temperature, excitation peripheral porphyrin moiety...

A molecule-based binary half-adder with optical inputs and outputs has been demonstrated. The consists of two photochromic organic molecules in solution a third-harmonic-generating crystal. One substance acts as an AND Boolean logic gate the other XOR gate. Inputs are laser pulses at 1064 or 532 nm that initiate photoisomerization reactions. Outputs absorbance fullerene radical anion (AND gate) fluorescence porphyrin (XOR gate). system carries out addition based on input pulses. Half-adders...

A photochromic nitrospiropyran moiety (Sp) has been covalently linked to a zinc (PZn) and free-base (PH2) porphyrin. In the resulting dyads (PZn−Spc PH2−Spc), porphyrin first excited singlet states are unperturbed by closed form of attached spiropyran. Excitation spiropyran either dyad in near-UV region results ring opening merocyanine (P−Spo) that absorbs at 600 nm. The open re-closes thermally 2-methyltetrahydrofuran with time constant 20 s, or following irradiation into nm band. yields...

One molecule acts as both an AND and XOR Boolean logic gate that share the same two photonic inputs. The comprises a half-adder, adding binary digits with only light inputs outputs, consists of three covalently linked photochromic moieties, spiropyran quinoline-derived dihydroindolizines. function is based on absorption properties molecule, whereas off−on−off response fluorescence to results from interchromophore excited-state quenching interactions. half-adder simple operate can be cycled...

A molecular triad consisting of a porphyrin (P) covalently linked to two photochromes-one from the dihydroindolizine family (DHI) and one dihydropyrene (DHP)-has been synthesized found act as either AND logic gate or an INHIBIT gate, depending on inputs initial state photochromes. The basis these functions is quenching fluorescence (output gates) by spiro form DHI does not quench fluorescence, whereas its betaine isomer strongly quenches photoinduced electron transfer. DHP also but...

Under excess illumination, plant photosystem II dissipates energy through the quenching of chlorophyll fluorescence, a process known as nonphotochemical quenching. Activation has been linked to conversion carotenoid with conjugation length nine double bonds (violaxanthin) into an 11-double-bond (zeaxanthin). It suggested that increase in turns from nonquencher quencher singlet excited states, but unequivocal evidence is lacking. Here, we present transient absorption spectroscopic study on...

In order to ensure efficient utilization of the solar spectrum, photosynthetic organisms use a variety antenna chromophores absorb light and transfer excitation reaction center, where photoinduced charge separation occurs. Reported here is synthetic molecular heptad that features two bis(phenylethynyl)anthracene borondipyrromethene antennas linked hexaphenylbenzene core also bears zinc porphyrins. A fullerene electron acceptor self-assembles both porhyrins via dative bonds. Excitation energy...

Photosynthetic reaction centers convert excitation energy from absorbed sunlight into chemical potential in the form of a charge-separated state. The rates electron transfer reactions necessary to achieve long-lived, high-energy states with high quantum yields are determined part by precise control electronic coupling among chromophores, donors, and acceptors energetics. Successful artificial photosynthetic for solar conversion have similar requirements. Control particular necessitates...

A novel scanning probe microscope stage permits break junction measurements of single molecule conductance while the molecules are illuminated with visible light. We studied a porphyrin-fullerene dyad designed to form charge separated state on illumination. significant fraction become more conductive, returning lower in dark, suggesting formation long-lived indium–tin oxide surface. Transient absorption spectra these molecular layers consistent state, finding implications for design...

Photonic control of photoinduced electron transfer has been demonstrated in a dimethyldihydropyrene (DHP) porphyrin (P) fullerene (C(60)) molecular triad. In the DHP-P-C(60) form triad, excitation moiety is followed by to give DHP-P(*)(+)-C(60)(*)(-) charge-separated state, which evolves charge shift reaction DHP(*)(+)-P-C(60)(*)(-). This final state lifetime 2 micros and formed an overall yield 94%. Visible (>or=300 nm) irradiation triad leads photoisomerization DHP cyclophanediene (CPD)....

Artificial light-harvesting constructs were synthesized by covalently linking two carotenoids to the central silicon atom of a phthalocyanine (Pc) derivative. Triad 1 binds having nine conjugated double bonds, whereas triad 2 10 carbon−carbon bonds in conjugation. Fluorescence excitation experiments indicated that, dissolved n-hexane, carotenoid Pc singlet energy transfer efficiency is ca. 92%, 2, it 30%. Results from ultrafast laser spectroscopy indicate that upon population optically...

Abstract A new photosynthetic reaction center mimic consisting of a porphyrin (P) linked to both fullerene electron acceptor (C 60 ) and carotenoid secondary donor (C) was synthesized studied in 2‐methyltetrahydrofuran using transient spectroscopic methods. Excitation the is followed by photoinduced transfer (τ = 32 ps) yield C–P ·+ –C ·− . Electron from carotene radical cation 125 gives final C –P–C state with an overall 0.95. This decays give triplet time constant 57 ns. The molecular...

One mechanism used by plants to protect against damage from excess sunlight is called nonphotochemical quenching (NPQ). Triggered low pH in the thylakoid lumen, NPQ leads conversion of excitation energy antenna system heat before it can initiate production harmful chemical species photosynthetic reaction centers. Here we report a synthetic hexad molecule that functionally mimics role NPQ. When dissolved an organic solvent, five zinc porphyrin moieties absorb light, exchange energy, and...

A series of phthalocyanine−carotenoid dyads in which a phenylamino group links phthalocyanine to carotenoids having 8−11 backbone double bonds were examined by visible and near-infrared femtosecond pump−probe spectroscopy combined with global fitting analysis. The molecules has permitted investigation the role quenching excited states cyclic tetrapyrroles. transient behavior varied dramatically length carotenoid solvent environment. Clear spectroscopic signatures radical species revealed...

A molecular double-throw switch that employs a photochromic moiety to direct photoinduced electron transfer from an excited state donor down either of two pathways has been prepared. The triad consists free base porphyrin (P) linked both C(60) acceptor and dihydroindolizine (DHI) photochrome. Excitation the DHI-P-C(60) results in with time constant 2.3 ns give DHI-P(*)(+)-C(60)(*)(-) charge-separated quantum yield 82%. UV (366 nm) light photoisomerizes DHI betaine (BT) form, which higher...

A porphyrin (P) has been covalently linked to a photochromic dihydroindolizine moiety (DHI) form P-DHI dyad. When the is in its closed, spirocyclic (DHIc), photophysics of attached are unaffected. Irradiation with UV light opens betaine (DHIo), which significantly higher reduction potential than DHIc. Light absorption by P-DHIo followed rapid (50 ps) photoinduced electron transfer yield P•+-DHIo•- charge-separated state. This state recombines 2.9 ps give ground at wavelengths >590 nm induces...

We present results from transient absorption spectroscopy on a series of artificial light-harvesting dyads made up zinc phthalocyanine (Pc) covalently linked to carotenoids with 9, 10, or 11 conjugated carbon−carbon double bonds, referred as 1, 2, and 3, respectively. assessed the energy transfer excited-state deactivation pathways following excitation strongly allowed carotenoid S2 state function conjugation length. The rapidly relaxes S* S1 states. In all systems we detected new pathway...

A photoelectrochemical biofuel cell has been developed which incorporates aspects of both an enzymatic and a dye-sensitized solar cell. Photon absorption at porphyrin-sensitized n-type semiconductor electrode gives rise to charge-separated state. Electrons holes are shuttled appropriate cathodic anodic catalysts, respectively, allowing the production electricity, or reduced fuel, via photochemical oxidation biomass-derived substrate. The operation this device is reviewed. use alternate redox...

The conversion of tyrosine to the corresponding tyrosyl radical in photosytem II (PSII) is an example proton-coupled electron transfer. Although moiety (TyrZ) known function as a redox mediator between photo-oxidized primary donor (P680•+) and Mn-containing oxygen-evolving complex, protonation states involved course reaction remain active area investigation. Herein, we report on optical, structural, electrochemical properties tyrosine−histidine constructs, which model their naturally...

In photosynthesis, sunlight is absorbed mainly by antenna chromophores that transfer singlet excitation energy to reaction centers for conversion useful electrochemical energy. Antennas may likewise be in artificial photosynthetic systems use make fuels or electricity. Here, we report the synthesis and spectroscopic properties of a molecular hexad comprising two porphyrin moieties four coumarin chromophores, all organized central hexaphenylbenzene core. Light any coumarins transferred on...