One-Step Cascade Synthesis of ortho-bay-Imidazolo-Extended Perylene Biscarboximides (OBISIM) and Their Application as Broad-Spectrum Fluorescent Dyes.

A one-step synthesis of perylene dyes with lateral extension by condensed imidazoles in a cascade reaction of sodium amide and benzonitrile is described in which multiple extensions can be controlled by the reaction conditions. The extensions lead to bathochromic shifts in absorption and fluorescence while maintaining high fluorescence quantum yields. The condensed imidazole units cause additional absorption bands in the hypsochromic visible region, resulting in broad-band absorbers. Multiple extensions of the aromatic system enable the NIR spectral approach of the spectra. Energy transfer (fluorescence resonance energy transfer, FRET) of dyads with perylene biscarboximides is very efficient and achieves quantum yields close to unity regardless of the lengths and orientation of the spacer. Applications as broad-band-absorbing fluorescent dyes, such as in solar collectors, are discussed.

Vibronic Intramolecular Resonant Energy Transfer along More than 5 nm: Synthesis of Dyads for a Re-Examination of the Distance Function of FRET.

Dyads of chromophores with orthogonal transition moments and sequences of aliphatic cage-structures as spacers were prepared where resonance energy transfer (FRET) proceeded in contrast to Förster's theory even until 58 Å. The distance dependence of the efficiency was re-examined by means of various functions; the commonly used R-6 dependence gave acceptable results, but a slightly larger exponent was more useful for practical applications.

OrthoFRET in Diamantane FRET in Orthogonal Stiff Dyads; Diamond Restriction for Frozen Vibrations.

Energy transfer proceeds in orthogonal dyads in contrast to Förster's theory and cannot be prohibited even by rigid interconnecting cage compounds such as cubane or diamantane.

FRET in Dyads with Orthogonal Chromophores and Minimal Spectral Overlap.

A dyad of orthogonally arranged chromophores of benzoperylenehexacarboxylictrisimide (energy donor, D) and terrylenetetracarboxylic bisimide (energy acceptor, A) was synthesized where a quantitative energy transfer (FRET) from D to A was found, although not only are both transition moments orthogonally arranged but the spectral overlap between the fluorescence of the energy donor and the absorption of the acceptor is also small. Even an appreciable further diminishing of the overlap in a dyad with phenylbenzoxazole as the donor could not inhibit the energy transfer. Thus, the application of the FRET theory to real systems is estimated to be limited where molecular vibrations seem to play a key role in the energy transfer.

Light-Driven Molecular Dynamics in Perylenes with Medium-Controlled Emission.

Highly fluorescent light emitters with medium-tunable clear colors were obtained from the skeleton of perylenedicarboximide by the attachment of donor-substituted aryl groups at the peri-position. The 4-methoxynaphthyl derivative 3a is preferred because of its strong solvatochromism in fluorescence where a mechanism of incomplete PLICT is made responsible both for the large Stokes' shift and the strong medium influence on fluorescence, allowing the fine tuning of color.

Switch-On Fluorescence of a Perylene-Dye-Functionalized Metal-Organic Framework through Postsynthetic Modification.

A perylene dye was introduced directly as a linker into a metal-organic framework (MOF) during synthesis. Depending on the dye concentration in the MOF synthesis mixture, different fluorescent materials were generated. The successful incorporation of the dye was proven by using (13) C and (27) Al MAS NMR spectroscopy, by solution NMR spectroscopy after digestion of the MOF sample, and by synthesizing a reference dye without connecting groups, which could coordinate on the metal-oxo cluster inside the MOF. Fluorescence quenching effects of the MOF linker, 2-aminoterephthalate, were observed and overcome by postsynthetic modification with acetic anhydride. We show here for the first time that amino groups, which can be used as anchoring points for covalent attachment of other molecules, are responsible for fluorescence quenching. Thus, a very promising strategy to implement switchable fluorescence into MOFs is shown here.

Sexterrylenetetracarboxylic Bisimides: NIR Dyes.

Sexterrylenehexacarboxylic bisimides, extended peri-arylenes with the alignment of six peri-arranged naphthalene units, were prepared by Suzuki cross coupling and subsequent oxidative ring closure reactions of the perylene units and exhibit NIR absorption at 945 nm. Intermediates are strongly fluorescent with an increased Stokes shift because of dynamic processes.

Hole-transfer induced energy transfer in perylene diimide dyads with a donor-spacer-acceptor motif.

We investigate the photoinduced dynamics of perylene diimide dyads based on a donor-spacer-acceptor motif with polyyne spacers of varying length by pump-probe spectroscopy, time resolved fluorescence, chemical variation and quantum chemistry. While the dyads with pyridine based polyyne spacers undergo energy transfer with near-unity quantum efficiency, in the dyads with phenyl based polyyne spacers the energy transfer efficiency drops below 50%. This suggests the presence of a competing electron transfer process from the spacer to the energy donor as the excitation sink. Transient absorption spectra, however, reveal that the spacer actually mediates the energy transfer dynamics. The ground state bleach features of the polyyne spacers appear due to the electron transfer decay with the same time constant present in the rise of the ground state bleach and stimulated emission of the perylene energy acceptor. Although the electron transfer process initially quenches the fluorescence of the donor it does not inhibit energy transfer to the perylene energy acceptor. The transient signatures reveal that electron and energy transfer processes are sequential and indicate that the donor-spacer electron transfer state itself is responsible for the energy transfer. Through the introduction of a Dexter blocker unit into the spacer we can clearly exclude any through bond Dexter-type energy transfer. Ab initio calculations on the donor-spacer and the donor-spacer-acceptor systems reveal the existence of a bright charge transfer state that is close in energy to the locally excited state of the acceptor. Multipole-multipole interactions between the bright charge transfer state and the acceptor state enable the energy transfer. We term this mechanism coupled hole-transfer FRET. These dyads represent a first example that shows how electron transfer can be connected to energy transfer for use in novel photovoltaic and optoelectronic devices.

How many molecular layers of polar solvent molecules control chemistry? The concept of compensating dipoles.

The extension of the solvent influence of the shell into the volume of a polar medium was examined by means of anti-collinear dipoles on the basis of the E(T)(30) solvent polarity scale (i.e., the molar energy of excitation of a pyridinium-N-phenolatebetaine dye; generally: E(T) =28,591 nm kcal mol(-1)/λmax) where no compensation effects were found. As a consequence, solvent polarity effects are concentrated to a very thin layer of a few thousand picometres around the solute where extensions into the bulk solvent become unimportant. A parallelism to the thin surface layer of water to the gas phase is discussed.

Chromophores arranged as "magnetic meta atoms": building blocks for molecular metamaterials.

Benzoperylenetriscarboximides were parallel arranged by stiff spacers where exciton interactions could be controlled by their distance. The most bathochromic electronic transition of the chromophores essentially exhibits only an electric component where an orthogonal magnetic component was established by the distance-controlled interaction of chromophores. Such arrangements were discussed as building blocks for molecular metamaterials.

Substitution of aromatics by amines at room temperature with negative energy of activation: amino peri-arylenes as metal-free components for dye-sensitized solar cells.

Substitution reactions of the chemically and photochemically unusually stable perylenetetracarboxylic bisimides proceed with neat amines even below room temperature where negative effective energies of activation were found. Analogous reactions proceed with naphthalenecarboximides as the lower homologues and terrylene and quaterrylene carboximides as the higher homologues. Bathochromically absorbing dyes with a novel pattern of substitution were obtained suitable as efficient metal-free light-absorbers for dye-sensitized solar cells.

Photoinduced processes in a dyad made of a linear and an angular perylene bisimide.

A dyad (PI0-PIa) made of a linear (PI0) and an angular (PIa) perylene biscarboximide is synthesized and its spectroscopic, electrochemical and photophysical properties investigated in solvents of various polarity. PIa is characterized by a high intersystem crossing. The spectroscopy and electrochemistry data point to a modest electronic coupling. LUMO-LUMO electron transfer from the singlet excited state PI0-¹PIa is thermodynamically feasible in polar solvents but its occurrence is precluded by a very fast energy transfer to yield ¹PI0-PIa, k(en) ≥ 10(11) s(-1). A HOMO-HOMO electron transfer in the latter state in polar solvents is precluded by the poor driving force, the reaction being unable to compete with the radiative deactivation of the excited state. The efficient energy transfer process is quantitatively examined in the frame of current theories and ascribed to a dipole-dipole (Förster) mechanism.

Reply to "Comment on 'Dependence of the Fluorescent Lifetime τ on the Concentration at High Dilution'": Extended Interpretation.

In "Comment on 'Dependence of the Fluorescent Lifetime τ on the Concentration at High Dilution'" by Anne Myers Kelley and David F. Kelley, the newly found concentration dependence of the fluorescence lifetime was attributed to the reabsorption and the delay of re-emission of fluorescence light. Accordingly, a comparably high optical density is required for a damping of the optically exciting light beam, causing a special profile for the re-emitted light with partial multiple reabsorption. However, an extended recalculation and re-examination on the basis of experimental spectra and the initially published data indicated an only static filtering effect by some reabsorption of fluorescent light. The resulting dynamic refluorescence is isotropically emitted in all room directions where only a small share of 0.006-0.6% adds to the measured primary fluorescence so that an interference in the measurement of fluorescent lifetimes becomes unimportant. Thus, the initially published data were further supported. The discrepancy between the two controversial papers could be resolved in terms of the different considered optical densities: a comparably high optical density can explain the interpretation of Kelley and Kelley, whereas low optical densities enabled by the use of the highly fluorescent perylene dye support our interpretation of the concentration dependence of the fluorescent lifetime.

Isolating Pure Donor and Acceptor Signals by Polarization-Controlled Transient Absorption Spectroscopy.

The optical spectra of molecules are often highly congested, inhibiting definite assignment of features and dynamics. In this work, we demonstrate and apply a polarization-based strategy for the decomposition of time-resolved optical spectra to analyze the electronic structure and energy transfer in a molecular donor-acceptor (D-A) dyad. We choose a dyad with orthogonal transition dipole moments for D and A and high fluorescence quantum yield to show that polarization-controlled ultrafast transient absorption spectra can isolate the pure D and A parts of the total signal. This provides a strategy to greatly reduce spectral congestion in complex systems and thus allows for detailed studies of electronic structure and electronic energy transfer.

Angular benzoperylenetetracarboxylic bisimides.

Benzoperylene derivatives with two angularly attached dicarboxylic imide rings, which were prepared by the Diels-Alder-reaction, exhibit strong fluorescence and their free peri positions allow either control of the UV/Vis spectra through their substituents or form anchor positions for the attachment of functional units. The angular chromophore 3 may be used both for fluorescent labeling such as for primary amines or enzymes or as building blocks for more complex assemblies where they may act as energy donors for FRET or electron acceptors in PET such as for photovoltaic solar cells.

Controlling UV/vis absorption and Stokes shifts in highly fluorescent chromophores by molecular dynamics in targeted construction of dyads.

Perylenedicarboximides were interlinked in their free peri-position to form dyads where the UV/vis absorptivity was amplified by exciton effects and the strong fluorescence bathochromically shifted by molecular dynamics. Applications of this type of dye with such increased Stokes shifts were discussed.

Noncovalent control of absorption and fluorescence spectra.

Perylene dyes with N-tert-alkyl substituents were prepared in which noncovalent interactions of the crowded substituent cause a variation of the geometry of the core and induce hypsochromic shifts in absorption and fluorescence. The interpretation of the shifts was supported by means of DFT calculations and an X-ray crystal structure analysis.

Photophysical and redox properties of perylene bis- and tris-dicarboximide fluorophores with triplet state formation: transient absorption and singlet oxygen sensitization.

A detailed photophysical characterization of a couple of new perylene imide derivatives, a carboxylic trisimide PIx, and an asymmetrically substituted carboxylic bisimide PIa is presented. PIx and PIa have the lowest singlet excited state just below 2.6 eV. The dyes are remarkably fluorescent (ϕ(f) = 0.37 ± 0.03 for PIa and ϕ(f) = 0.58 ± 0.04 for PIx in toluene), but they also display an efficient intersystem crossing. This leads to typical excited triplet photophysics/photochemistry, with intense triplet state absorption spectra and efficient singlet oxygen ((1)Δ(g)) photosensitization (ϕ(Δ) = 0.68 ± 0.02 for PIa and 0.44 ± 0.02 for PIx in toluene). On the basis of the measured ϕ(Δ), a ϕ(isc) of 0.65 ± 0.02 for PIa and 0.43 ± 0.02 for PIx in toluene is derived. PIx reduces at -0.58 eV vs SCE, almost similarly to the corresponding symmetrically substituted perylene bisimide PI0, but unlike the latter, it has the first oxidation potential above +1.9 V. PIa is more electron rich and displays a more difficult first reduction at -0.95 V with a more facile oxidation at +1.75 V, similar to that of the parent PI0. The absorption spectra of the excited singlet and triplet states and that of electrochemically generated monoanions are reported.

Synthesis, staining properties, and biocompatibility of a new cyanine dye for ILM peeling.

BACKGROUND: The aim of this work is to investigate the biocompatibility and staining properties of DSS: 3,3'-Di-(4-sulfobutyl)-1,1,1',1'-tetramethyl-di-1H-benz[e]indocarbocyanine (DSS). METHODS: Dye concentrations of 0.5, 0.25, and 0.1% were evaluated (290 and 295 mOsm). Toxicity was assessed using a colorimetric test measuring the inhibition of ARPE 19 cell, human primary RPE cell, and human Müller cell proliferation. Exposure time was 30, 60, 120, and 300 s. Indocyanine green (ICG) (0.5, 0.25, and 0.1%) served as a control. Cells were also illuminated with plain white light (750 mW/cm(2)) for 10 min to assess phototoxic effects. Besides staining of porcine and human lens capsule, internal limiting membrane (ILM)-staining was assessed by applying 0.25 and 0.5% DSS over the macula in two human post-mortem eyes. RESULTS: DSS of 0.25 and 0.1% showed no toxic effect on primary RPE cells and MIO-M1cells, and 0.5, 0.25, and 0.1% for ARPE-19 cells. In MIO-M1cells, 0.5% dye showed a significant reduction of mitochondrial dehydrogenase activity only following an exposure time of 300 s. Following illumination, ICG showed a significantly more pronounced effect on cell viability in primary RPE cells and MIO-M1cells compared to DSS. The absorption maximum is found at 591 nm; the even more bathochromic fluorescence proceeds with a common Stokes' shift where maxima at 620 and 660 nm with a quantum yield of 32% were found. The fluorescence is sufficiently hypsochromic and the fluorescence quantum yield high enough for an easy visual detection. The contrast and staining properties at the ILM were excellent and allowed for a controlled removal of the ILM during surgery. No penetration into deeper retinal layers was noted. CONCLUSIONS: Our results indicate that this new cyanine dye DSS may represent an alternative for ILM staining due to its matched absorption concerning visibility and fluorescence qualities as well as its good biocompatibility.

Dependence of the Fluorescent Lifetime τ on the Concentration at High Dilution.

Long-range interactions between electronically excited molecules and molecules at the ground state were found for distances of much more than 100 nm, as indicated by the dependence of the fluorescence lifetime on the concentration of dyes in diluted solutions. In contrast to this experimental result, the fluorescence lifetimes of distant isolated molecules should be independent from the concentration according to basic theory for light emission, such as that reported by Förster and Strickler-Berg. As a consequence, the theory of such emission should be modified for real systems to include electromagnetic interactions with distant resonating structures. Consequences of these findings concern many subjects, such as imaging methods (FLIM) in biochemistry.