Synthesis and Characterization of Dendritic Multichromophores Based on Rylene Dyes for Vectorial Transduction of Excitation Energy

Multi-stimuli programmable FRET based RGB absorbing antennae towards ratiometric temperature, pH and multiple metal ion sensing

A red-green-blue (RGB) multichromophoric antenna 1 consisting of energy donors naphthalimides and perylenediimides and a central aza-BODIPY energy acceptor along with two subchromophoric red-blue (RB 6) and green-blue (GB 12) antennae was designed that showed efficient cascade Förster resonance energy transfer (FRET). RGB antenna 1 showed pronounced temperature-dependent emission behaviour where emission intensities in green and red channels could be tuned in opposite directions by temperature giving rise to unique ratiometric sensing with a temperature sensitivity of 0.4% °C. RGB antenna 1 showed reversible absorption modulation selectively in the blue region (RGB ↔ RG) upon acid/base addition giving rise to pH sensing behaviour. Furthermore, RGB antenna 1 was utilized to selectively sense metal ions such as Co2+ and Fe3+ through a FRET turn-off mechanism induced by a redox process at the aza-BODIPY site that resulted in the selective spectral modulation of the red band (i.e., RGB → GB). Model antenna RB 6 showed white light emission with chromaticity coordinates (0.32, 0.33) on acid addition. Antennae 1, 6 and 12 also exhibited solution state electrochromic switching characterized by distinct colour changes upon changing the potential. Finally, antennae 1, 6 and 12 served as reversible fluorescent inks in PMMA/antenna blends whereby the emission colours could be switched or tuned using different stimuli such as acid vapour, temperature and metal ions.

Hexaarylbenzene based high-performance p-channel molecules for electronic applications

Hexaarylbenzene-based molecules find potential applications in organic electronics due to wider energy gap, high HOMO level, higher photoconductivity, electron-rich nature, and high hole-transporting property. Due to the unique propeller structure, these molecules show low susceptibility towards self-aggregation. This property can be tailored by proper molecular engineering by the incorporation of appropriate groups. Therefore, hexaarylbenzene chromophores are widely used as the materials for high-efficiency light-emitting materials, charge transport materials, host materials, redox materials, photochemical switches, and molecular receptors. This review highlights the diverse structural modification techniques used for the synthesis of symmetrical and unsymmetrical structures. Also, the potential applications of these molecules in organic light-emitting diodes, organic field-effect transistors, organic photovoltaics, organic memory devices, and logic circuits are discussed.

Synthesis of diverse heterocyclic frameworks using cyclopentadienones via the Diels–Alder strategy

In this review article, we briefly summarize the versatility of Diels–Alder reactions of cyclopentadienones and concise routes to diverse hetero-atom bearing PAHs using cyclones as building blocks.

Photophysics of perylene monoimide-labelled organocatalysts

A fluorophore-tagged organocatalyst undergoes electron transfer in polar solvents allowing to sense the presence of its free quinuclidine catalytic site.

Rylene annulated phthalocyanine: a fully conjugated block for the construction of a supramolecular two-dimensional framework

A rylene annulated phthalocyanine (ZnPcPDI4) was designed and synthesized. Single-crystal X-ray diffraction analyses unambiguously confirmed the giant molecule quasi-planar "four leaf clover" skeleton with a 27 Å diameter and a two-dimensional cage-like supramolecular structure. The fully conjugated characteristics endowed it with significant Q-band red-shifts to the near-infrared region of 785 nm, and a largely degenerated LUMO level.

Cell membrane permeable fluorescent perylene bisimide derivatives for cell lysosome imaging

The cellular uptake of Lyso-APBIprobes is improved by PEG chains, and the double morpholine moieties make Lyso-APBI probes have higher acid activation ratio and better cell lysosome specificity.

The polar side of polyphenylene dendrimers

The site-specific functionalization of poly(phenylene) dendrimers can produce macromolecules with a range of different polarities.

Energy flow dynamics within cofacial and slip-stacked perylene-3,4-dicarboximide dimer models of π-aggregates

Robust perylene-3,4-dicarboximide (PMI) π-aggregates provide important light-harvesting and electron-hole pair generation advantages in organic photovoltaics and related applications, but relatively few studies have focused on the electronic interactions between PMI chromophores. In contrast, structure-function relationships based on π-π stacking in the related perylene-3,4:9,10-bis(dicarboximides) (PDIs) have been widely investigated. The performance of both PMI and PDI derivatives in organic devices may be limited by the formation of low-energy excimer trap states in morphologies where interchromophore coupling is strong. Here, five covalently bound PMI dimers with varying degrees of electronic interaction were studied to probe the relative chromophore orientations that lead to excimer energy trap states. Femtosecond near-infrared transient absorption spectroscopy was used to observe the growth of a low-energy transition at ~1450-1520 nm characteristic of the excimer state in these covalent dimers. The excimer-state absorption appears in ~1 ps, followed by conformational relaxation over 8-17 ps. The excimer state then decays in 6.9-12.8 ns, as measured by time-resolved fluorescence spectroscopy. The excimer lifetimes reach a maximum for a slip-stacked geometry in which the two PMI molecules are displaced along their long axes by one phenyl group (~4.3 Å). Additional displacement of the PMIs by a biphenyl spacer along the long axis prevents excimer formation. Symmetry-breaking charge transfer is not observed in any of the PMI dimers, and only a small triplet yield (<5%) is observed for the cofacial PMI dimers. These data provide structural insights for minimizing excimer trap states in organic devices based on PMI derivatives.

Energy transfer at the single-molecule level: synthesis of a donor-acceptor dyad from perylene and terrylene diimides

In 2004, we reported single-pair fluorescence resonance energy transfer (spFRET), based on a perylene diimide (PDI) and terrylene diimide (TDI) dyad (1) that was bridged by a rigid substituted para-terphenyl spacer. Since then, several further single-molecule-level investigations on this specific compound have been performed. Herein, we focus on the synthesis of this dyad and the different approaches that can be employed. An optimized reaction pathway was chosen, considering the solubilities, reactivities, and accessibilities of the building blocks for each individual reaction whilst still using established synthetic techniques, including imidization, Suzuki coupling, and cyclization reactions. The key differentiating consideration in this approach to the synthesis of dyad 1 is the introduction of functional groups in a nonsymmetrical manner onto either the perylene diimide or the terrylene diimide by using imidization reactions. Combined with well-defined purification conditions, this modified approach allows dyad 1 to be obtained in reasonable quantities in good yield.

Thermally-Polymerized Rylene Nanoparticles

Rylene dyes functionalized with varying numbers of phenyl trifluorovinylether (TFVE) moieties were subjected to a thermal emulsion polymerization to yield shape-persistent, water-soluble chromophore nanoparticles. Perylene and terrylene diimide derivatives containing either two or four phenyl TFVE functional groups were synthesized and subjected to thermal emulsion polymerization in tetraglyme. Dynamic light scattering measurements indicated that particles with sizes ranging from 70 - 100 nm were obtained in tetraglyme, depending on monomer concentration. The photophysical properties of individual monomers were preserved in the nanoemulsions and emission colors could be tuned between yellow, orange, red, and deep red. The nanoparticles were found to retain their shape upon dissolution into water and the resulting water suspensions displayed moderate to high fluorescence quantum yield.

Two-dimensional self-assembly of linear molecular rods at the liquid/solid interface

We report on the synthesis and scanning tunneling microscopy (STM) studies of a series of linear molecular rods (1-5) comprising different numbers and/or spatial arrangements of perfluorinated benzene and benzene subunits interlinked with diacetylenes in the para position and decorated with or without terminal dodecyl chains. The molecules organize themselves into well-ordered 2D crystal structures at the liquid/solid interface through intermolecular and molecule-substrate interactions. Whereas the molecules substituted by dodecyl chains form the lamellar structures with alternating rigid core rows and alkyl chain rows, the unsubstituted ones change the orientation of the rigid backbones with respect to the lamellar axis. The molecular arrangement is not influenced by fluoro substituents on any phenyl ring of the backbone, which suggests that the interactions between the π-conjugated backbones are dominated by close packing rather than by the dipole moments of the rods or fluorine-based intermolecular interactions.

N-(2-(N',N'-diethylamino)ethyl)perylene-3,4-dicarboximide and its quaternized derivatives as fluorescence probes of acid, temperature, and solvent polarity

In this manuscript, we report the fluorescence properties of N-(2-(N',N'-diethylamino)ethyl)perylene-3,4-dicarboximide (1) and its quaternized derivative N-(2-(N',N'- diethyl-N'-methylammonium)ethyl)perylene-3,4-dicarboximide tosylate (2) in organic solvents. The effects of carboxylic acids and amines on the fluorescence properties of these compounds were investigated. In addition, we studied the aggregation and fluorescence properties of (2) and its 9-bromo-substituted derivative (3) in aqueous solution. The fluorescent properties of these compounds change dramatically with the extent of aggregation, thus allowing these compounds to be used as fluorescent probes for changes in temperature and solvent polarity. For instance, the fluorescence emission intensity of 3 increases by about 28 times as the temperature of the solution increases from 10°C to 85°C. The fluorescent intensities of 2 and 3 in methanol are higher than that in water by about 8 and 25 times, respectively.

Conjugation of fluorescent proteins with DNA oligonucleotides

This work describes the synthesis of covalent ssDNA conjugates of six fluorescent proteins, ECFP, EGFP, E(2)GFP, mDsRed, Dronpa, and mCherry, which were cloned with an accessible C-terminal cystein residue to enable site-selective coupling using a heterobispecific cross-linker. The resulting conjugates revealed similar fluorescence emission intensity to the unconjugated proteins, and the functionality of the tethered oligonucleotide was proven by specific Watson-Crick base pairing to cDNA-modified gold nanoparticles. Fluorescence spectroscopy analysis indicated that the fluorescence of the FP is quenched by the gold particle, and the extent of quenching varied with the intrinsic spectroscopic properties of FP as well as with the configuration of surface attachment. Since this study demonstrates that biological fluorophores can be selectively incorporated into and optically coupled with nanoparticle-based devices, applications in DNA-based nanofabrication can be foreseen.

Photophysics and redox properties of rylene imide and diimide dyes alkylated ortho to the imide groups

Ruthenium-catalyzed C-H bond activation was used to directly attach phenethyl groups derived from styrene to positions ortho to the imide groups in a variety of rylene imides and diimides including naphthalene-1,8-dicarboximide (NMI), naphthalene-1,4:5,8-bis(dicarboximide) (NI), perylene-3,4-dicarboximide (PMI), perylene-3,4:9,10-bis(dicarboximide) (PDI), and terrylene-3,4:11,12-bis(dicarboximide) (TDI). The monoimides were dialkylated, while the diimides were tetraalkylated, with the exception of NI, which could only be dialkylated due to steric hindrance. The absorption, fluorescence, transient absorption spectra, and lowest excited singlet state lifetimes of these chromophores, with the exception of NI, are nearly identical to those of their unsubstituted parent chromophores. The reduction potentials of the dialkylated chromophores are approximately 100 mV more negative and oxidation potentials are approximately 40 mV less positive than those of the parent compounds, while the corresponding potentials of the tetraalkylated compounds are approximately 200 mV more negative and approximately 100 mV less positive than those of their parent compounds, respectively. Continuous wave electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) data on the radical anion of PDI reveals spin density on the perylene-core protons as well as on the beta-protons of the phenethyl groups. The phenethyl groups enhance the otherwise poor solubility of the bis(dicarboximide) chromophores and only weakly perturb the photophysical and redox properties of the parent molecules, rendering these derivatives and related molecules of significant interest to solar energy conversion.

Mimics of the self-assembling chlorosomal bacteriochlorophylls: regio- and stereoselective synthesis and stereoanalysis of acyl(1-hydroxyalkyl)porphyrins

Diacylation of copper 10,20-bis(3,5-di-tert-butylphenylporphyrin) using Friedel-Crafts conditions at short reaction times, high concentrations of catalyst, and 0-4 degrees C affords only the 3,17-diacyl-substituted porphyrins, out of the 12 possible regioisomers. At longer reaction times and higher temperatures, the 3,13-diacyl compounds are also formed, and the two isomers can be conveniently separated by normal chromatographic techniques. Monoreduction of these diketones affords in good yields the corresponding acyl(1-hydroxyalkyl)porphyrins, which after zinc metalation are mimics of the natural chlorosomal bacteriochlorophyll (BChl) d. Racemate resolution by HPLC on a variety of chiral columns was achieved and further optimized, thus permitting easy access to enantiopure porphyrins. Enantioselective reductions proved to be less effective in this respect, giving moderate yields and only 79% ee in the best case. The absolute configuration of the 3(1)-stereocenter was assigned by independent chemical and spectroscopic methods. Self-assembly of a variety of these zinc BChl d mimics proves that a collinear arrangement of the hydroxyalkyl substituent with the zinc atom and the carbonyl substituent is not a stringent requirement, since both the 3,13 and the 3,17 regioisomers self-assemble readily as the racemates. Interestingly, the separated enantiomers self-assemble less readily, as judged by absorption, fluorescence, and transmission electron microscopy studies. Circular dichroism spectra of the self-assemblies show intense Cotton effects, which are mirror-images for the two 3(1)-enantiomers, proving that the supramolecular chirality is dependent on the configuration at the 3(1)-stereocenter. Upon disruption of these self-assemblies with methanol, which competes with zinc ligation, only very weak monomeric Cotton effects are present. The favored heterochiral self-assembly process may also be encountered for the natural BChls. This touches upon the long-standing problem of why both 3(1)-epimers are encountered in BChls in ratios that vary with the illumination and culturing conditions.

An efficient synthesis of quaterrylenedicarboximide NIR dyes

Quaterrylenedicarboximides were prepared from 9-bromoperylene-3,4-dicarboximides by palladium-catalyzed coupling with 3-perylene boronic ester, followed by oxidative cyclodehydrogenation of the resulting perylene-perylenedicarboximide dyads with iron(III) chloride. The quaterrylenedicarboximides, described here, are highly photochemically and thermally stable dyes, which may be useful as green NIR dyes (lambdamax = 735 nm) and as building blocks for the synthesis of higher rylene dyes.

Multichromophoric Polyphenylene Dendrimers: Toward Brilliant Light Emitters with an Increased Number of Fluorophores

Two routes for the introduction of highly fluorescent peryleneimide chromophores into the scaffolding of polyphenylene dendrimers via iterative Diels-Alder cycloadditions are presented. The key intermediates for the divergent dendrimer buildup were two cyclopentadienone branching units carrying two peryleneimides and two masked terminal alkynes. The difference between the two reagents is the mode of incorporation of the chromophores. In the first case, the chromophores were attached to the alpha-position of the tetraphenylcyclopentadienones. In the second case, peryleneimides are used as a "spacer" in the beta-position of the cyclopentadienones giving rise to dendrimers with extended molecular diameters (up to 12 nm) and 24 chromophores within their scaffold. Absorption and emission characteristics of the new multichromophoric nanoparticles were investigated and compared to those of the parent dyes. Additionally, an asymmetrically substituted first-generation dendrimer with six perylene diimide chromophores and one ester functionality is reported. The ester serves as a potential anchor group, and this nanoemitter paves the way to a multichromophoric fluorescence label. All dendrimers have good solubility in common organic solvents, high fluorescence quantum yields, and defined distances between the chromophores, making them attractive candidates for single-molecule spectroscopy.

A Simple Multichromophore Design for Energy Transfer in Distyrylbenzenes with Pyrene Pendants

A set of Don --> Acc <-- Don multichromophores was synthesized based on a simple design with two pyrene donors (absorbing antennae) connected to a bis-1,4-(3,4,5-trimethoxystyryl)benzene core acceptor using various flexible, nonconjugated tethers. Excitation of the pyrene donors at 276 nm in solution yields near exclusive emission from the core chromophore at 445-450 nm, with energy transfer efficiencies up to 92%, far better than achieved with simple mixtures. The simple tethering design imposes a high "local" concentration of the pyrene near the acceptor core unit that is maintained even at very low multichromophore concentrations. Solvent effects on absorption and emission spectra are very small, except in cases where a pi-conjugating O-C=O moiety of the tethering group is directly attached to the core chromophore, rather than being placed in the middle of the tether. Energy transfer in the systems is effective due to good donor-acceptor energy matching. The optimal energy transfer efficiency was achieved using an eight-atom flexible linker.

Dendrimer Analogues of Linear Molecules to Evaluate Energy and Charge-Transfer Properties

[reaction: see text] We have designed and synthesized difunctionalized dendrimers containing two donors in the periphery and an acceptor at the core to serve as scaffolds for comparison with linear analogues to investigate the advantage of dendritic scaffolds for energy and charge transfer. Comparison of these dendrimers with the fully decorated dendrimers provides information on the advantage of chromophore density in energy/charge transfer from periphery to the core.

Structurally Characterized Hetero-Oligopolyphenylenes: Synthetic Advances Toward Next-Generation Heterosuperbenzenes

The successful Diels-Alder [2+4] cycloaddition of dipyrimidyl acetylene and suitably substituted 2,3,4,5-tetraarylcyclopenta-2,4-dien-1-ones (3-7) generates a series of selectively functionalized hexaarylbenzenes. Each has two pairs of peripheral functional groups (R' and R=tert-butyl 8 and R=methyl 9, methoxy 10, bromo 11, triisopropylsilylethynyl 12) and four ortho-imine nitrogen atoms. The dibromo derivative 11 is a useful precursor for the formation of a mono ethynyl 13 and diethynyl 14 substituted polyphenylene. Changing the dienophile to di(2-thienyl)acetylene gives an S-heteroatom polyphenylene 15. The compounds were fully characterized by using (1)H, (13)C and a range of 2 D NMR spectroscopic techniques, elemental analysis, and mass spectrometry. Oxidative cyclodehydrogenation of dimethoxy hexaphenylbenzene 10 by using iron(III) chloride results in the formation of a spirocyclic dienone 16, which in a separate reaction undergoes dienone/phenol rearrangement to give the first 4-fused-ring, N-heterosuperbenzene (HSB) 17. Six single crystal molecular structures reveal the commonality of unidirectional twisting of the external aromatic rings in these heteroatom polyphenylenes. The twist angles and any H-bonding or interdigitation in these structures are discussed.

Light harvesting dendrimers

Tree-like dendrimers with decreasing number of chromophores from periphery to core is an attractive candidate for light-harvesting applications. Numerous dendritic designs with different kinds of light-collecting chromophores at periphery and an energy-sink at the core have been demonstrated with high energy transfer efficiency. These building blocks are now being developed for several applications such as light-emitting diodes, frequency converters and other photonic devices. This review outlines the efforts that are based on both conjugated and non-conjugated dendrimers.

Dibenzopentarylenebis(dicarboximide)s: Novel near-infrared absorbing dyes

The facile synthesis of the new class of core-extended rylene chromophores, dibenzopentarylenebis(dicarboximide)s, having an intense absorption at 1020-1040 nm, is presented.