Self-assembly of supramolecular light-harvesting arrays from covalent multi-chromophore perylene-3,4:9,10-bis(dicarboximide) building blocks

We report on two multi-chromophore building blocks that self-assemble in solution and on surfaces into supramolecular light-harvesting arrays. Each building block is based on perylene-3,4:9,10-bis(dicarboximide) (PDI) chromophores. In one building block, N-phenyl PDI chromophores are attached at their para positions to both nitrogens and the 3 and 6 carbons of pyromellitimide to form a cross-shaped molecule (PI-PDI(4)). In the second building block, N-phenyl PDI chromophores are attached at their para positions to both nitrogens and the 1 and 7 carbons of a fifth PDI to produce a saddle-shaped molecule (PDI(5)). These molecules self-assemble into partially ordered dimeric structures (PI-PDI(4))(2) and (PDI(5))(2) in toluene and 2-methyltetrahydrofuran solutions with the PDI molecules approximately parallel to one another primarily due to pi-pi interactions between adjacent PDI chromophores. On hydrophobic surfaces, PDI(5) grows into rod-shaped nanostructures of average length 130 nm as revealed by atomic force microscopy. Photoexcitation of these supramolecular dimers in solution gives direct evidence of strong pi-pi interactions between the excited PDI chromophore and other PDI molecules nearby based on the observed formation of an excimer-like state in <130 fs with a lifetime of about 20 ns. Multiple photoexcitations of the supramolecular dimers lead to fast singlet-singlet annihilation of the excimer-like state, which occurs with exciton hopping times of about 5 ps, which are comparable to those observed in photosynthetic light-harvesting proteins from green plants.     

Fullerene C60-perylene-3,4:9,10-bis(dicarboximide) light-harvesting dyads: spacer-length and bay-substituent effects on intramolecular singlet and triplet energy transfer

Novel covalent fullerene C(60)-perylene-3,4:9,10-bis(dicarboximide) (C(60)-PDI) dyads (1-4) were synthesized and characterized. Their electrochemical and photophysical properties were investigated. Electrochemical studies show that the reduction potential of PDI can be tuned relative to C(60) by molecular engineering through altering the substituents on the PDI bay region. It was demonstrated using steady-state and time-resolved spectroscopy that a quantitative, photoinduced energy transfer takes place from the PDI moiety, acting as a light-harvesting antenna, to the C(60) unit, playing the role of energy acceptor. The bay-substitution (tetrachloro [1 and 2] or tetra-tert-butylphenoxy [3 and 4]) of the PDI antenna and the linkage length (C(2) [1 and 3] or C(5) [2 and 4]) to the C(60) acceptor are important parameters in the kinetics of energy transfer. Femtosecond transient absorption spectroscopy indicates singlet-singlet energy-transfer times (from the PDI to the C(60) unit) of 0.4 and 5 ps (1), 4.5 and 27 ps (2), 0.8 and 12 ps (3), and 7 and 50 ps (4), these values being ascribed to two different conformers for each C(60)-PDI system. Subsequent triplet-triplet energy-transfer times (from the C(60) unit to the PDI) are slower and in the order of 0.8 ns (1), 6.2 ns (2), 2.7 ns (3), and 9 ns (4). Nanosecond transient absorption spectroscopy of final PDI triplet states show a marked influence of the bay substitution (tetrachloro- or tetra-tert-butylphenoxy), and triplet-state lifetimes (10-20 micros) and the PDI triplet quantum yields (0.75-0.52) were estimated. The spectroscopy showed no substantial solvent effect upon comparing toluene (non-polar) to benzonitrile (polar), indicating that no electron transfer is occurring in these systems.     

Synthesis and characterization of solution-processable core-cyanated perylene-3,4;9,10-bis(dicarboximide) derivatives

Core-cyanated perylene-3,4;9,10-bis(carboxyimide) derivatives N-functionalized with tethered anthracenes (PDI3A-CN(2), PDI4A-CN(2)) and the corresponding solution-processable cycloadduct precursors (PDI3A-CA-CN(2), PDI4A-CA-CN(2)) were synthesized and their optical, electrochemical, and thermal properties characterized. These derivatives exhibit HOMO-LUMO energy gaps of ～2.1-2.3 eV and first reduction potentials between -50 and -150 mV versus SCE. The PDI3A-CN(2) and PDI4A-CN(2) cycloadducts are soluble in common organic solvents (>50 mg/mL), and the corresponding spin-coated films are converted to PDI3A-CN(2) and PDI4A-CN(2) films upon thermal annealing.     

Perylene-3,4:9,10-bis(dicarboximide) linked to [60]fullerene as a light-harvesting antenna

New [60]fullerene-perylene-3,4:9,10-bis(dicarboximide) dyads 1 and 2 are described in the search of an energy transfer from the dye as a photoactive antenna to the fullerene moiety.     

Competition between singlet fission and charge separation in solution-processed blend films of 6,13-bis(triisopropylsilylethynyl)pentacene with sterically-encumbered perylene-3,4:9,10-bis(dicarboximide)s

The photophysics and morphology of thin films of N,N-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-bis(dicarboximide) (1) and the 1,7-diphenyl (2) and 1,7-bis(3,5-di-tert-butylphenyl) (3) derivatives blended with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) were studied for their potential use as photoactive layers in organic photovoltaic (OPV) devices. Increasing the steric bulk of the 1,7-substituents of the perylene-3,4:9,10-bis(dicarboximide) (PDI) impedes aggregation in the solid state. Film characterization data using both atomic force microscopy and X-ray diffraction showed that decreasing the PDI aggregation by increasing the steric bulk in the order 1 < 2 < 3 correlates with a decrease in the density/size of crystalline TIPS-Pn domains. Transient absorption spectroscopy was performed on ~100 nm solution-processed TIPS-Pn:PDI blend films to characterize the charge separation dynamics. These results showed that selective excitation of the TIPS-Pn results in competition between ultrafast singlet fission ((1*)TIPS-Pn + TIPS-Pn → 2 (3*)TIPS-Pn) and charge transfer from (1*)TIPS-Pn to PDIs 1-3. As the blend films become more homogeneous across the series TIPS-Pn:PDI 1 → 2 → 3, charge separation becomes competitive with singlet fission. Ultrafast charge separation forms the geminate radical ion pair state (1)(TIPS-Pn(+?)-PDI(-?)) that undergoes radical pair intersystem crossing to form (3)(TIPS-Pn(+?)-PDI(-?)), which then undergoes charge recombination to yield either (3*)PDI or (3*)TIPS-Pn. Energy transfer from (3*)PDI to TIPS-Pn also yields (3*)TIPS-Pn. These results show that multiple pathways produce the (3*)TIPS-Pn state, so that OPV design strategies based on this system must utilize this triplet state for charge separation.     

Tetrathiafulvalene in a perylene-3,4:9,10-bis(dicarboximide)-based dyad: a new reversible fluorescence-redox dependent molecular system

A donor-acceptor dyad system involving tetrathiafulvalene (TTF) as donor attached by a flexible spacer to perylene-3,4:9,10-bis(dicarboximide) (PDI) as acceptor was synthesized and characterized. The strategy used the preliminary synthesis of an unsymmetrical PDI unit bearing an alcohol functionality as anchor group. Single-crystal analysis revealed a highly organized arrangement in which all PDI molecules are packed in a noncentrosymmetrical pattern. It was shown that the fluorescence emission intensity of the TTF-PDI dyad can be reversibly tuned depending on the oxidation states of the TTF unit. This behavior is attributed to peculiar properties of TTF linked to a PDI acceptor, which fluoresces intrinsically. Consequently, this dyad can be considered as a new reversible fluorescence-redox dependent molecular system.     

Excited singlet states of covalently bound, cofacial dimers and trimers of perylene-3,4:9,10-bis(dicarboximide)s

Perylene-3,4:9,10-bis(dicarboximide) (PDI) and its derivatives are robust organic dyes that strongly absorb visible light and display a strong tendency to self-assemble into ordered aggregates, having significant interest as photoactive materials in a wide variety of organic electronics. To better understand the nature of the electronics states produced by photoexcitation of such aggregates, the photophysics of a series of covalent, cofacially oriented, pi-stacked dimers and trimers of PDI and 1,7-bis(3',5'-di-t-butylphenoxy)perylene-3,4:9,10-bis(dicarboximide) (PPDI) were characterized using both time-resolved absorption and fluorescence spectroscopy. The covalent linkage between the chromophores was accomplished using 9,9-dimethylxanthene spacers. Placing n-octyl groups on the imide nitrogen atoms at the end of the PDI chromophores not attached to the xanthene spacer results in PDI dimers having near optimal pi-stacking, leading to formation of a low-energy excimer-like state, while substituting the more sterically demanding 12-tricosanyl group on the imides causes deviations from the optimum that result in slower formation of an excimer-like excited state having somewhat higher energy. By comparison, PPDI dimers having terminal n-octyl imide groups have two isomers, whose photophysical properties depend on the ability of the phenoxy groups at the 1,7-positions to modify the pi stacking of the PPDI molecules. In general, disruption of optimal pi-stacking by steric interactions of the phenoxy side groups results in excimer-like states that are higher in energy. The corresponding lowest excited singlet states of the PDI and PPDI trimers are dimer-like in nature and suggest that structural distortions that accompany formation of the trimers are sufficient to confine the electronic interaction on two chromophores within these systems. This further suggests that it may be useful to build into oligomeric PDI and PPDI systems some degree of flexibility that allows the structural relaxations necessary to promote electronic interactions between multiple chromophores.     

Bis(n-octylamino)perylene-3,4:9,10-bis(dicarboximide)s and their radical cations: synthesis, electrochemistry, and ENDOR spectroscopy

1,6- and 1,7-bis(n-octylamino)perylene-3,4:9,10-bis(dicarboximide) were synthesized by reaction of n-octylamine with the corresponding dibromo compounds. These compounds display intense charge-transfer optical transitions in the visible spectrum (approximately 550-750 nm) and fluoresce weakly (Phi(F) < 0.06). Cyclic voltammetry reveals that each chromophore undergoes facile and reversible oxidation and reduction. Spectroelectrochemical studies show that the radical cations of these chromophores are stable and show no signs of deprotonation of the secondary amines. Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) studies of the chemically generated radical cations of these chromophores corroborate the spectroelectrochemical data by showing that the radical cations persist for days at room temperature in methylene chloride solution. These experiments and complementary density functional theory (DFT) calculations provide a comprehensive picture of the molecular orbitals, spin density distributions, and geometries of the radical cations. The redox properties and stability of these alkylamino-functionalized perylene compounds make them a valuable addition to the family of robust perylene-based chromophores that can be used to develop new photoactive charge transport materials.     

Intense Dyes through Chromophore–Chromophore Interactions: Bi- and Trichromophoric Perylene-3,4:9,10-bis(dicarboximide)s

Simple perylene dyes , which are known for their high extinction coefficients, are converted into intense and highly fluorescent (at ca. 540 nm) dyes such as 1 by a directed chromophore–chromophore coupling. Molar extinction coefficients of more than 400 000 L mol⁻¹ cm⁻¹ are attained. R = CH(C₆H₁₃)₂, CH(C₇H₁₅)₂, CH(C₉H₁₉)₂.     

6,13-dibromopentacene [2,3:9,10]-bis(dicarboximide): a versatile building block for stable pentacene derivatives

6,13-Dibromopentacene [2,3:9,10]-bis(dicarboximide) (1) was synthesized for the first time by using in situ generated benzo[1,2-c:4,5-c']difuran as a key intermediate. Compound 1 exhibits good photostability in comparison to other pentacene derivatives and it can be further functionalized by Pd-catalyzed coupling reactions to give a series of soluble and stable functional pentacenes.     

Crystal structure of N,N,N',N'-tetrakis(methyldiphenylphosphino)-bis(2'-phenoxy)-3,6-dioxaoctane.

The title molecule, [C70H68N2O4P4], is a polydentate podand consisting of four etheral oxygens, two tertiary amine nitrogens and four diphenylphosphin groups. It crystallizes in the triclinic space group P1, and there is only one half a molecule in the asymmetric unit. The coordinations around the N and P atoms are pyramidal. The conformations about C20-C21, O2-C21 and O2-C22 are gauche, anti and anti, respectively.     

Multiple photosynthetic reaction centres composed of supramolecular assemblies of zinc porphyrin dendrimers with a fullerene acceptor

Multiple photosynthetic reaction centres have successfully been constructed using supramolecular complexes of zinc porphyrin dendrimers [D(ZnP)(n): n = 4, 8, 16] with fulleropyrrolidine bearing a pyridine ligand (C(60)py). Efficient energy migration occurs completely between the ZnP units of dendrimers prior to the electron transfer with increasing the generation of dendrimers to attain an extremely long charge-separation lifetime.     

Reaction of metal-binding ligands with the zinc proteome: zinc sensors and N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine

The commonly used Zn(2+) sensors 6-methoxy-8-p-toluenesulfonamidoquinoline (TSQ) and Zinquin have been shown to image zinc proteins as a result of the formation of sensor-zinc-protein ternary adducts not Zn(TSQ)(2) or Zn(Zinquin)(2) complexes. The powerful, cell-permeant chelating agent N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) is also used in conjunction with these and other Zn(2+) sensors to validate that the observed fluorescence enhancement seen with the sensors depends on intracellular interaction with Zn(2+). We demonstrated that the kinetics of the reaction of TPEN with cells pretreated with TSQ or Zinquin was not consistent with its reaction with Zn(TSQ)(2) or Zn(Zinquin)(2). Instead, TPEN and other chelating agents extract between 25 and 35% of the Zn(2+) bound to the proteome, including zinc(2+) from zinc metallothionein, and thereby quench some, but not all, of the sensor-zinc-protein fluorescence. Another mechanism in which TPEN exchanges with TSQ or Zinquin to form TPEN-zinc-protein adducts found support in the reactions of TPEN with Zinquin-zinc-alcohol dehydrogenase. TPEN also removed one of the two Zn(2+) ions per monomer from zinc-alcohol dehydrogenase and zinc-alkaline phosphatase, consistent with its ligand substitution reactivity with the zinc proteome.     

N-茄呢基-N,N′-二(3,4-二甲氧基苄基)乙二胺的合成

癌症仍是需要攻克的医学难题之一. 虽然已有多种抗癌剂用于临床,但大多数抗癌剂是以细胞毒性来抑制癌细胞的繁殖,使用剂量受到限制,长期治疗还会产生毒副作用. 研究表明,N-茄呢基-N,N′-二(3,4-二甲氧基苄基)乙二胺(简称SDB-乙二胺)[1]具有优先作用于多种抗药性肿瘤的直接的细胞毒性,对几乎所有类型临床抗肿瘤药物具有增效作用,其中对抗生素类和生物碱类抗癌药物的增效尤为显著,如对其中的博莱霉素(争光霉素)、呱来霉素、磅霉素等,每毫升注射液含有3和10 μg的SDB-乙二胺,药效分别能提高47和130倍,对新制癌菌素(neocarzinostatin)也能提高2倍以上[2]. 与其他增效剂相比,SDB-乙二胺的增效作用具有定向细胞毒性,而本身完全没有细胞毒性,安全性好,可以连续使用,可减少抗癌剂的剂量,减轻毒副作用[3]. 因此,研究开发抗癌药物增效剂是癌症治疗的发展方向之一.     

Synthesis and recognition properties of a ruthenium(II)-bis(zinc) cyclic porphyrin trimer

A series of cyclic metalloporphyrin trimers containing one Ru(II)-CO porphyrin center are synthesized. A stepwise convergent route is used to synthesize Ru(CO)Zn(2)2.Py3T, where tripyridyltriazine (Py3T) templates the formation of the trimer and forces the CO group to the outside of the cavity. Three mixed-metal trimers, Ru(CO)Zn(2)2, Ru(CO)Ni(2)2, and Ru(CO)Mg(2)2, are synthesized from Ru(CO)Zn(2)2.Py3T and are characterized by NMR, UV-visible, and fluorescence spectroscopy. The Ru(CO)Zn(2)2 trimer is found to bind Py3T very tightly (K approximately 10(12) M-1), the resultant complex dissociating very slowly (kdissoc approximately 3 x 10(-7) s-1) in CDCl3 at 60 degrees C. During the course of these studies, the binding selectivity of a ruthenium porphyrin monomer, Ru(CO)3, for pyridine over THF is estimated to be ca. 7 x 10(4):1.     

Rational design of supramolecular chirality in porphyrin assemblies: the halogen bond case

Asymmetric functionalization of the tetraarylporphyrin scaffold, combined with directional supramolecular halogen bonding, yields chiral architectures.