The Excited-State N-H Tautomerization Rate in Free-Base Corroles.

Corrole is a tetrapyrrolic dye with a structure that resembles porphyrin, apart from a single missing carbon. The absence of this carbon results in the re-arrangement of the double bonds within the macrocycle, and the presence of three pyrrolic protons in the central cavity in its free-base form. These protons lead to the existence of two distinct tautomeric structures that exist in a dynamic equilibrium.

Strong Host-Guest Dependence on the Emissive Properties of MOF-5 and [Zn(BTTB)(DMF)•(HO)].

3D-[ZnO(1,4-BDC)•(solvent)] (; BDC = benzodicarboxylate) and -[Zn(BTTB)(DMF)•(HO)] (; BTTB = 4,4',4″,4‴-benzene-1,2,4,5-tetrayltetrabenzoate) have been investigated by means of steady-state UV-visible and fluorescence and time-resolved emission spectroscopy, as a function of solvent and power of the excitation irradiation. The low-temperature X-ray structures (173 K) were permitted to locate solvent molecules (here HO) in the lattice. They were found distributed in the middle in the voids with no evidence of specific interactions (H-bond, coulombic, and dipole-dipole) with the framework.

A Fused Poly(truncated rhombic dodecahedron)-Containing 3D Coordination Polymer: A Multifunctional Material with Exceptional Properties.

The design of new and inexpensive metal-containing functional materials is of great interest. Herein is reported a unique thermochromic near-IR emitting coordination polymer, 3D-[CuI()], , which is formed when ArS(CH)SAr (, Ar = 4-CHOMe) reacts with 2 equiv of CuI in EtCN. In MeCN, ([CuI()(MeCN)], consisting of an alternating [-CuI--CuI--] chain where the CuI cubane units bear two metal-bound MeCN molecules, is formed.

Modulating the Photophysical Properties and Electron Transfer Rates in Diketopyrrolopyrrole-Based Coordination Polymers.

Molecular self-assembly through noncovalent interactions is a particularly efficient approach to fine-tune the optoelectronic and photophysical properties of electroactive materials. In metal-ligand coordination polymers, the final properties of the assemblies are directly related to the nature of the metal-ligand interaction. To probe for such influence on the photophysical properties of electroactive materials, a series of coordination polymers based on a well-known organic dye, diketopyrrolopyrrole, was prepared through coordination of a terpyridine-containing monomer with various metal sources, including iron, cobalt, zinc, and manganese.

Photophysical and Optical Properties of Semiconducting Polymer Nanoparticles Prepared from Hyaluronic Acid and Polysorbate 80.

A nanoprecipitation procedure was utilized to prepare novel diketopyrrolopyrrole-based semiconducting polymer nanoparticles (SPNs) with hyaluronic acid (HA) and polysorbate 80. The nanoprecipitation led to the formation of spherical nanoparticles with average diameters ranging from 100 to 200 nm, and a careful control over the structure of the parent conjugated polymers was performed to probe the influence of π-conjugation on the final photophysical and thermal stability of the resulting SPNs. Upon generation of a series of novel SPNs, the optical and photophysical properties of the new nanomaterials were probed in solution using various techniques including transmission electron microscopy, dynamic light scattering, small-angle neutron scattering, transient absorption, and UV-vis spectroscopy.

Unusual triplet-triplet annihilation in a 3D copper(i) chloride coordination polymer.

A new coordination polymer (CP) defined as [CuCl(EtS(CH)SEt)] (CP2) was prepared by reacting EtS(CH)SEt with CuCl in acetonitrile in a 1 : 2 stoichiometric ratio. The X-ray structure reveals formation of non-porous 3D material composed of parallel 2D-[CuClS] layers of Cl-bridged Cu(μ-Cl) rhomboids assembled by EtS(CH)SEt ligands. A weak triplet emission (Φ < 0.

What does it take to induce equilibrium in bidirectional energy transfers?

Two dyads built with a co-facial slipped bis(zinc(ii)porphyrin), a free base and a bridge, [Zn2]-bridge-[Fb] (bridge = C6H4C[triple bond, length as m-dash]C, 1 and C6H4C[triple bond, length as m-dash]CC6H4, 2), exhibit S1 energy equilibrium [Zn2]* ↔ [Fb]* at 298 K, an extremely rare situation, which depends on the degree of MO coupling between the units. At 77 K, 2 becomes bi-directional due to the two large C6H4-[Zn2] and C6H4-[Fb] dihedral angles.

Is π-Stacking Prone To Accelerate Singlet-Singlet Energy Transfers?

π-Stacking is the most common structural feature that dictates the optical and electronic properties of chromophores in the solid state. Herein, a unidirectional singlet-singlet energy-transfer dyad has been designed to test the effect of π-stacking of zinc(II) porphyrin, [Zn], as a slipped dimer acceptor using a BODIPY unit, [bod], as the donor, bridged by the linker CHC≡CCH. The rate of singlet energy transfer, k(S), at 298 K ( k(S) = 4.

Azophenine as Central Core for Efficient Light Harvesting Devices.

The notoriously non-luminescent uncycled azophenine (Q) was harnessed with Bodipy and zinc(II)porphyrin antennas to probe its fluorescence properties, its ability to act as a singlet excited state energy acceptor and to mediate the transfer. Two near-IR emissions are depicted from time-resolved fluorescence spectroscopy, which are most likely due to the presence of tautomers of very similar calculated total energies (350 cm ; DFT; B3LYP). The rates for energy transfer, k (S ), for Bodipy*→Q are in the order of 10 -10  s and are surprisingly fast when considering the low absorptivity properties of the lowest energy charge transfer excited state of azophenine.

Platinum Complexes of N,N',N″,N‴-Diboronazophenines.

Azophenine, (α-CHNH)(CH-N═CH═N-CH), well known to be non-emissive, was rigidified by replacing two amine protons by two difluoroboranes (BF) and further functionalized at the para-positions of the phenyl groups by luminescent trans-ArC≡C-Pt(PR)-C≡C ([Pt]) arms [Ar = CH (R = Et), hexa(n-hexyl)truxene) (Tru; R = Bu)]. Two effects are reported. First, the linking of these [Pt] arms with the central azophenine (CH-N═CH(NH)═N-CH; Q) generates very low energy charge-transfer (CT) singlet and triplet excited states (([Pt]-to-Q)*) with absorption bands extending all the way to 800 nm.

Increasing the lifetimes of charge separated states in porphyrin-fullerene polyads.

Two linear polyads were designed using zinc(ii)porphyrin, [ZnP], and N-methyl-2-phenyl-3,4-fullero-pyrrolidine (C) where C is dangling either at the terminal position of [ZnP]-CH-[triple bond, length as m-dash]-CH-[ZnP]-C (1) or at the central position of [ZnP]-CH-[triple bond, length as m-dash]-CH-[ZnP(C)]-CH-[triple bond, length as m-dash]-CH-[ZnP] (2) in order to test whether the fact of having one or two side electron donors influences the rate of electron transfer, k. These polyads were studied using cyclic voltammograms, DFT computations, steady state and time-resolved fluorescence spectroscopy, and femtosecond transient absorption spectroscopy (fs-TAS). Photo-induced electron transfer confirmed by the detection of the charge separated state [ZnP˙+]/C˙ from fs-TAS occurs with rates (k) of 3-4 × 10 s whereas the charge recombinations (CRs) are found to produce the [ZnP] ground state via two pathways (central [ZnP˙+]/C˙ (ps) and terminal central [ZnP˙+]/C˙ (ns) producing [1ZnP] (ground state) and [3ZnP*]).

Rendering cross-conjugated azophenine derivatives emissive to probe the silent photophysical properties of emeraldine.

An azophenine derivative was synthesized by coupling truxene and azophenine via the copper-free Sonagashira reaction using Pd(dba) and As(PPh) as catalysts. The crystal structure of this heavy azophenine model (∼4000) was made and the identity of the structure was confirmed. By introducing truxene groups into this cross-conjugated structure, the deactivating rotations around the NH-CH bonds were slowed down, which rendered this derivative near-IR emissive at 298 K.

Ferrocene-BODIPYmerocyanine dyads: new NIR absorbing platforms with optical properties susceptible to protonation.

Ferrocene-BODIPYmerocyanine dyads 5 and 6 were prepared and characterized by a variety of spectroscopic, electrochemical, and theoretical methods. Experimental and theoretical data on these NIR absorbing compounds are suggestive of unusual susceptibility (for BODIPY chromophores) of the delocalized π-system in 5 and 6 to protonation and low-potential oxidation of their π-systems.

Application of the boron center for the design of a covalently bonded closely spaced triad of porphyrin-fullerene mediated by dipyrromethane.

Two novel triads had been designed through covalent bond connection of the boron dipyrromethane (BODIPY), free base porphyrin (H2P) or zinc(ii) porphyrin (ZnP) and N-methyl-2-phenyl-3,4-fulleropyrrolidine (C) mediated by BODIPY. This closely spaced triad arrangement where porphyrin and fullerene are placed apart is anticipated to stabilize charge separation by separating the two radicals from each other. Two model polyads were synthesized with BODIPY and H2P or ZnP to investigate interaction between the two chromophores.

Dense ionization and subsequent non-homogeneous radical-mediated chemistry of femtosecond laser-induced low density plasma in aqueous solutions: synthesis of colloidal gold.

The "cold" low density plasma channels generated by the filamentation of powerful femtosecond laser pulses in aqueous solutions constitute a source of dense ionization. Here, we probed the radiation-assisted chemistry of water triggered by laser ionization via the radical-mediated synthesis of nanoparticles in gold chloride aqueous solutions. We showed that the formation of colloidal gold originates from the reduction of trivalent ionic gold initially present in solution by the reactive radicals (e.

Metal Dependence on the Bidirectionality and Reversibility of the Singlet Energy Transfer in Artificial Special Pair-Containing Dyads.

The demetalation of a precursor dyad, 3, built upon a zinc(II)-containing artificial special pair and free-base antenna, leads to a new dyad, 4, for singlet energy transfer composed of cofacial free-base porphyrins (acceptor), [Fb] bridged by a 1,4-CH group to a free-base antenna (donor), [Fb]. This dyad exhibits the general structure [M]-CH-[Fb], where [M] = [Fb], and completes a series reported earlier, where [M] = [Mg] (2) and [Zn] (3). The latter dyads exhibit a bidirectional energy-transfer process at 298 K for 2 and at 77 K for 3.

Excited State N-H Tautomer Selectivity in the Singlet Energy Transfer of a Zinc(II)-Porphyrin-Truxene-Corrole Assembly.

An original corrole-containing polyad for S energy transfer, in which one zinc(II)-porphyrin donor is linked to two free-base corrole acceptors by a truxene linker, is reported. This polyad exhibits a rapid zinc(II)-porphyrin*→free-base corrole transfer (4.83×10  s ; 298 K), even faster than the tautomerization in the excited state processes taking advantage of the good electronic communication provided by the truxene bridge.

Ultrafast energy and electron transfers in structurally well addressable BODIPY-porphyrin-fullerene polyads.

Two electron transfer polyads built upon [C]-[ZnP]-[BODIPY] (1) and [ZnP]-[ZnP](-[BODIPY])(-[C]) (2), where [C] = N-methyl-2-phenyl-3,4-fulleropyrrolidine, [BODIPY] = boron dipyrromethane, and [ZnP] = zinc(ii) porphyrin, were synthesized along with their corresponding energy transfer polyads [ZnP]-[BODIPY] (1a) and [ZnP]-[ZnP]-[BODIPY] (2a) as well as relevant models. These polyads were studied using cyclic voltammetry, DFT computations, steady state and time-resolved fluorescence spectroscopy, and fs transient absorption spectroscopy. The rates for energy transfer, k, [BODIPY]* → [ZnP] are ∼2.

The 3D [(CuBr){μ-EtS(CH)SEt}] material: a rare example of a coordination polymer exhibiting triplet-triplet annihilation.

EtS(CH)SEt, L1, forms with CuI a luminescent 2D polymer [CuI{μ-L1}] (CP1), which exhibits no triplet excitation energy migration, but with CuBr, it forms a 3D material (CP2), [(CuBr){μ-L1}] consisting of parallel (CuBrS) layers bridged by L1's. CP2 shows T-T annihilation at 298 K but not at 77 K.

Ultrafast Singlet Energy Transfer in Porphyrin Dyads.

A weakly fluorescent Pt-bridged dyad composed of zinc(II) porphyrin (Zn; donor) and free base (Fb; acceptor) has been designed and exhibits an ultrafast singlet energy transfer between porphyrins. The use of larger atoms within the central linker significantly increases the MO coupling between the two chromophores and inherently the electronic communication.

Metal Linkage Effects on Ultrafast Energy Transfer.

We report the preparation of several new porphyrin homodimers bridged by a platinum(II) ion in which very intense electronic communication through the coordination link occurs. Moreover, the synthesis of a new porphyrin dyad and its photophysical properties are reported. This dyad exhibits the fastest singlet energy transfer ever reported for synthetic systems between a zinc(II) porphyrin and a porphyrin free base.

Triplet Energy Transfers in Well-Defined Host-Guest Porphyrin-Carboxylate/Cluster Assemblies.

The dyes (5-(4-carboxylphenyl)-10,15,20-tritolylporphyrinato)zinc(II) (MCP) and (5,15-bis(4-carboxylphenyl)-15,20-ditolylporphyrinato)zinc(II) (DCP), as their sodium salts, were used to form assemblies with the unsaturated cluster Pd3(dppm)3(CO)(2+) ([Pd3(2+)], dppm = (Ph2P)2CH2) via ionic CO2(-)···Pd3(2+) interactions. The photophysical properties in their triplet states were studied. The position of the T1 state of [Pd3(2+)] (∼8190 cm(-1)) has been proposed using DFT computations and was corroborated by the presence of a Tn → S0 delayed emission at 680-700 nm arising from a T1-T1 annihilation process at 77 K.

Electron-Transfer Kinetics within Supramolecular Assemblies of Donor Tetrapyrrolytic Dyes and an Acceptor Palladium Cluster.

9,18,27,36-Tetrakis[meso-(4-carboxyphenyl)]tetrabenzoporphyrinatozinc(II) (TCPBP, as a sodium salt) was prepared in order to compare its photoinduced electron-transfer behavior toward unsaturated cluster Pd3(dppm)3(CO)(2+) ([Pd3(2+)]; dppm = Ph2PCH2PPh2 as a PF6(-) salt) with that of 5,10,15,20-tetrakis[meso-(4-carboxyphenyl)]porphyrinatozinc(II) (TCPP) in nonluminescent assemblies of the type dye···[Pd3(2+)]x (x = 0-4; dye = TCPP and TCPBP) using femtosecond transient absorption spectroscopy. Binding constants extracted from UV-vis titration methods are the same as those extracted from fluorescence quenching measurements (static model), and both indicate that the TCPBP···[Pd3(2+)]x assemblies (K14 = 36000 M(-1)) are slightly more stable than those for TCPP···[Pd3(2+)]x (K14 = 27000 M(-1)). Density functional theory computations (B3LYP) corroborate this finding because the average ionic Pd···O distance is shorter in the TCPBP···[Pd3(2+)] assembly compared to that for TCPP···[Pd3(2+)].

Are the orientation and bond strength of the RCO2(-)···M link key factors for ultrafast electron transfers?

The photo-induced electron transfers in the "straight up" ionic assemblies [Pd3(2+)]···MCP and [Pd3(2+)]···DCP···[Pd3(2+)] ([Pd3(2+)]* → MCP or DCP) are ultrafast (<85 fs) indicating that it is not necessary to have a strong coordination bond or a bent geometry to obtain fast electron injection in porphyrin-containing DSSCs.