Synthesis and Optical Properties of Water‐Soluble Polyglycerol‐Dendronized Rylene Bisimide Dyes

Four new water‐soluble polyglycerol‐dendronized perylene, terrylene, and quaterrylene bisimides have been synthesized and characterized with respect to their optical properties in polar organic solvents and water by using UV/Vis and fluorescence spectroscopy. All of these dyes were highly soluble in water, but the size of the chosen polyglycerol dendron was only sufficient to completely suppress dye aggregation for the core‐unsubstituted perylene derivative. Their high solubility in water and their absorption and emission wavelengths up to the NIR region make the core‐unsubstituted perylene and terrylene bisimides ideal candidates for applications in bioimaging, whilst the lack of fluorescence for quaterrylene bisimide in all polar solvents does not warrant further investigation of this chromophore in fluorescence and imaging applications. Likewise, tuning of the emission of rylene bisimides towards longer wavelengths by employing electron‐donating bay substituents is not a promising strategy, owing to the lower fluorescence quantum yields in polar solvents and, in particular, in water.     

Control of Conformation and Chirality of Nonplanar π‐Conjugated Diporphyrins Using Substituents and Axial Ligands

Nonplanar conformations of pyrazine‐fused Zn^II diporphyrins could be controlled by the choice of the meso‐aryl substituents and an axial ligand on the central metals. Zn^II diporphyrins bearing sterically demanding meso‐aryl groups with ortho‐substituents led to a twisted chiral D₂ conformation, while an achiral C_2h form was preferred in the case of aryl groups without ortho‐substituents. Helical chirality induction on Zn^II diporphyrins in the twisted conformation was achieved by controlling their handedness of the molecular twist through coordination of optically active 1‐phenethylamine.     

Fused Perylene–Phthalocyanine Macrocycles: A New Family of NIR‐Dyes with Pronounced Basicity

The synthesis and characterization of a new type of chromophore, namely PePc consisting of a central phthalocyanine core and four fused perylene–bisimide (PBI) units is described for the first time. The entire architecture represents a highly extended conjugated heterocyclic π‐system with C_4h symmetry. In order to guarantee pronounced solubility in organic solvents the corresponding PBI units were bay‐functionalized with tert‐butylphenoxy substituents. Next to the metal‐free macrocycle, PePcH₂, also metallated macrocycles PePcM (M=Zn, Ni, Pb, Ru, Fe) were synthesized. The extensive fusion of the corresponding aromatic building blocks to the very large extended π‐system leads to a very narrow HOMO–LUMO gap and as a consequence to transparency in the visible but light absorption in the NIR region. Significantly, the azomethine N‐atoms N1?N4 of PePcM and PePcH₂ are highly basic. The corresponding tetraprotonated systems can only be deprotonated with very strong non‐nucleophilic bases such as phosphazene bases. In the protonated forms PePcMH₄⁴⁺ and PePcMH₆⁴⁺ the absorption maximum is shifted back to the visible region due to the loss of conjugation. The experimental findings were corroborated with quantum mechanical calculations.     

Introducing Perylene as a New Member to the Azaborine Family

Substitutional doping of perylene with two boron atoms at the 6b/12b positions and two oxygen or nitrogen atoms at the 1/7 positions has been achieved. The modular synthesis route developed for these bis‐BO‐ ( 3 ) and bis‐BN‐perylenes ( 5 ) starts from the readily accessible borinic acid derivative of the doubly brominated 9,10‐dihydro‐9,10‐diboraanthracene (DBA), 1,5‐Br₂DBA(OH)₂. A Stille‐type reaction first furnishes the alkynyl‐substituted species 1,5‐(RCC)₂DBA(OH)₂ ( 2 ), which undergo double ring closure to afford 3 via the gold‐catalyzed addition of the O?H bonds to the C≡C bonds. Treatment of 2 with MeN(SiMe₃)₂ leads to aminoborane intermediates 1,5‐(RCC)₂DBA(N(H)Me)₂, which can be ring‐closed to give 5 in a similar manner as in the case of 3 . Different substituents R (such as Me, tBuPh) can be introduced at the 2/8 positions of the perylene core. The products obtained undergo reversible reduction and are efficient blue/turquoise emitters.     

Computational studies on optoelectronic and charge transfer properties of some perylene‐based donor‐π‐acceptor systems for dye sensitized solar cell applications

We report DFT studies on some perylene‐based dyes for their electron transfer properties in solar cell applications. The study involves modeling of different donor‐π‐acceptor type sensitizers, with perylene as the donor, furan/pyrrole/thiophene as the π‐bridge and cyanoacrylic group as the acceptor. The effect of different π‐bridges and various substituents on the perylene donor was evaluated in terms of opto‐electronic and photovoltaic parameters such as HOMO‐LUMO energy gap, λ_max, light harvesting efficiency(LHE), electron injection efficiency (Ø_inject), excited state dye potential (E^dye*), reorganization energy(λ), and free energy of dye regeneration (). The effect of various substituents on the dye–I₂ interaction and hence recombination process was also evaluated. We found that the furan‐based dimethylamine derivative exhibits a better balance of the various optical and photovoltaic properties. Finally, we evaluated the overall opto‐electronic and transport parameters of the TiO₂‐dye assembly after anchoring the dyes on the model TiO₂ cluster assembly.     

Rainbow Perylene Monoimides: Easy Control of Optical Properties

Perylene dyes have been widely used as photoreceptors in organic photovoltaics because of their outstanding photo‐, thermal and chemical stability as well as their excellent photophysical properties. Herein we describe a novel generation of perylene dyes based on N‐(2,6‐diisopropylphenyl)‐perylene‐3,4‐dicarboximide. The optical properties of these novel perylenes can be finely tuned via the substituents in the 1‐, 6‐ and 9‐positions of the perylene core. The facile synthesis, tunable orbital and absorption properties, and electrochemical potentials help us to design efficient perylene sensitizers for solar‐cell applications.     

Pendant perylene polymers with high electron mobility

Four different perylene side‐chain semiconductor polymers, synthesized by a combination of “click” chemistry and nitroxide‐mediated radical polymerization, are compared in terms of their optical, electrochemical, and charge transport properties. The nature of the solubilizing side chains and the chromophoric π‐conjugation system of the pendant perylene moieties are systematically changed. Two poly(perylene bisimide)s with hydrophobic (PPBI 1) and hydrophilic substituents (PPBI 2) are compared with poly(perylene diester benzimidazole) (PPDEB) and poly(perylene diester imide) (PPDEI). Optical properties are investigated by UV/vis and photoluminescence spectroscopy, and charge transport is studied by organic field effect transistor and space‐charge‐limited current measurements. Cyclic voltammetry is used to estimate highest occupied molecular orbital and lowest unoccupied molecular orbital levels. The extended π‐conjugation system of PPDEB leads to a broader absorption in the visible region when compared with PPDEI and the PPBIs. Although absorption properties of PPDEB could be considerably improved by varying the perylene core, the charge carrier mobility could be drastically improved by tuning the substituents. Very high electron mobilities of 1 × 10^?2 cm² V^?1 s^?1 were achieved for PPBI 2 carrying oligoethyleneglycol substituents. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1480–1486     

2‐Bromo‐1,3‐bis[2‐(2‐naphthyl)vinyl]benzene benzene hemisolvate and 9‐bromodinaphth[1,2‐a:2′,1′‐j]anthracene

2‐Bromo‐1,3‐bis[2‐(2‐naphthyl)vinyl]benzene benzene hemisolvate, C₃₀H₂₁Br·0.5C₆H₆, (I), with two formula units in the asymmetric unit, exists in the crystal structure in a conformation in which the trans (2‐naphthyl)vinyl substituents on the central bromobenzene moiety appear as nearly fully extended `wings', while 9‐bromodinaphth[1,2‐a:2′,1′‐j]anthracene, C<sub>30</sub>H<sub>17</sub>Br, (II), adopts a highly nonplanar `manta‐ray' shape, with the H atoms in the interior of the molecule within van der Waals contact distances. The packing of the significantly twisted molecules of (I) generates large voids which are filled by benzene solvent molecules, while molecules of (II) stack compactly with all C—Br bonds parallel within the stack.     

para‐Quinodimethane‐Bridged Perylene Dimers and Pericondensed Quaterrylenes: The Effect of the Fusion Mode on the Ground States and Physical Properties

Polycyclic hydrocarbon compounds with a singlet biradical ground state show unique physical properties and promising material applications; therefore, it is important to understand the fundamental structure/biradical character/physical properties relationships. In this study, para‐quinodimethane (p‐QDM)‐bridged quinoidal perylene dimers 4 and 5 with different fusion modes and their corresponding aromatic counterparts, the pericondensed quaterrylenes 6 and 7 , were synthesized. Their ground‐state electronic structures and physical properties were studied by using various experiments assisted with DFT calculations. The proaromatic p‐QDM‐bridged perylene monoimide dimer 4 has a singlet biradical ground state with a small singlet/triplet energy gap (?2.97 kcal mol^?1), whereas the antiaromatic s‐indacene‐bridged N‐annulated perylene dimer 5 exists as a closed‐shell quinoid with an obvious intramolecular charge‐transfer character. Both of these dimers showed shorter singlet excited‐state lifetimes, larger two‐photon‐absorption cross sections, and smaller energy gaps than the corresponding aromatic quaterrylene derivatives 6 and 7 , respectively. Our studies revealed how the fusion mode and aromaticity affect the ground state and, consequently, the photophysical properties and electronic properties of a series of extended polycyclic hydrocarbon compounds.     

Mechanochromism,Twisted/Folded Structure Determination,and Derivatization of (N‐Phenylfluorenylidene)acridane

(N‐Phenylfluorenylidene)acridane (Ph‐FA) compounds with electron‐withdrawing and ‐donating substituents (H, MeO, Ph, NO₂, Br, F) at the para position of the phenyl group were successfully synthesized by Barton–Kellogg reactions of N‐aryl thioacridones and diazofluorene. By using the substituent on the nitrogen atom to alter the electronic properties, both the folded and twisted conformers of p‐NO₂‐C₆H₄‐FA could be crystallographically characterized, which enabled the charge transfer from the electron‐donating acridane moiety to the electron‐accepting fluorenylidene moiety to be understood. Ground‐state mechanochromism, thermochromism, vapochromism, and proton‐induced chromism were demonstrated between the folded and twisted conformations of the conformers. Protonation and chemical oxidation of Ph‐FA gave two stable acridinium compounds, namely, the fluorenylacridinium and acridinium radical cations. The present study will contribute to the development of functional dyes and organic semiconductors.     

Mechanochromism,Twisted/Folded Structure Determination,and Derivatization of (N‐Phenylfluorenylidene)acridane

(N‐Phenylfluorenylidene)acridane (Ph‐FA) compounds with electron‐withdrawing and ‐donating substituents (H, MeO, Ph, NO₂, Br, F) at the para position of the phenyl group were successfully synthesized by Barton–Kellogg reactions of N‐aryl thioacridones and diazofluorene. By using the substituent on the nitrogen atom to alter the electronic properties, both the folded and twisted conformers of p‐NO₂‐C₆H₄‐FA could be crystallographically characterized, which enabled the charge transfer from the electron‐donating acridane moiety to the electron‐accepting fluorenylidene moiety to be understood. Ground‐state mechanochromism, thermochromism, vapochromism, and proton‐induced chromism were demonstrated between the folded and twisted conformations of the conformers. Protonation and chemical oxidation of Ph‐FA gave two stable acridinium compounds, namely, the fluorenylacridinium and acridinium radical cations. The present study will contribute to the development of functional dyes and organic semiconductors.     

Photoinduced Electron Transfer in Perylene‐TiO2 Nanoassemblies

The photosensitization effect of three perylene dye derivatives on titanium dioxide nanoparticles (TiO₂ NPs) has been investigated. The dyes used, 1,7‐dibromoperylene‐3,4,9,10‐tetracarboxy dianhydride (1), 1,7‐dipyrrolidinylperylene‐3,4,9,10‐tetracarboxy dianhydride (2) and 1,7‐bis(4‐tert‐butylphenyloxy)perylene‐3,4,9,10‐tetracarboxy dianhydride (3) have in common bisanhydride groups that convert into TiO₂ binding groups upon hydrolysis. The different substituents on the bay position of the dyes enable tuning of their redox properties to yield significantly different driving forces for photoinduced electron transfer (P_eT). Recently developed TiO₂ NPs having a small average size and a narrow distribution (4 ± 1 nm) are used in this work to prepare the dye‐TiO₂ systems under study. Whereas successful sensitization was obtained with 1 and 2 as evidenced by steady‐state spectral shifts and transient absorption results, no evidence for the attachment of 3 to TiO₂ was observed. The comparison of the rates of P_eT (k_PeT) for 1‐ and 2‐TiO₂ systems studied in this work with those obtained for previously reported analogous systems, having TiO₂ NPs covered by a surfactant layer (Hernandez et al. [2012] J. Phys. Chem. B., 117, 4568–4581), indicates that k_PeT for the former systems is slower than that for the later. These results are interpreted in terms of the different energy values of the conduction band edge in each system.     

Pyrrolo[3,2‐b]pyrroles—From Unprecedented Solvatofluorochromism to Two‐Photon Absorption

A combined experimental and theoretical study of the two‐photon absorption (2PA) properties of a series of quadrupolar molecules possessing a highly electron‐rich heterocyclic core, pyrrolo[3,2‐b]pyrrole, is presented. In agreement with quantum‐chemical calculations, large 2PA cross‐section values, σ_2PA≈10²–10³ GM (1 GM=10⁵⁰ cm⁴ s photon^?1), are observed at wavelengths of 650–700 nm, which correspond to the two‐photon allowed but one‐photon forbidden transitions. The calculations also predict that increased planarity of this molecule through removal of two N‐substituents leads to further increase in the σ_2PA values. Surprisingly, the most quadrupolar pyrrolo[3,2‐b]pyrrole derivative, containing two 4‐nitrophenyl substituents at positions 2 and 5, demonstrates a very strong solvatofluorochromic effect, with a fluorescence quantum yield as high as 0.96 in cyclohexane, whereas the fluorescence vanishes in DMSO.     

Chemisorption,Morphology, and Structure of a n‐Type Perylene Diimide Derivative at the Interface with Gold: Influence on Devices from Thin Films to Single Molecules

We have investigated thin films of a perylene diimide derivative with a cyano‐functionalized core (PDI‐8CN₂) deposited on Au(111) single crystals from the monolayer to the multilayer regime. We found that PDI‐8CN₂ is chemisorbed on gold. The molecules experience a thickness‐dependent reorientation, and a 2D growth mode with molecular stepped terraces is achieved adopting low deposition rates. The obtained results are discussed in terms of their impact on field effect devices, also clarifying why the use of substrate/contact treatments, decoupling PDI‐8CN₂ molecules from the substrate/contacts, is beneficial for such devices. Our results also suggest that perylene diimide derivatives with CN bay‐functionalization are very promising candidates for single‐molecule electronic devices.     

Banana‐shaped molecules with 4,6‐dichlorinated central core: effect of lateral substituents and terminal chains on the formation of antiferroelectric smectic mesophases

Six banana‐shaped compounds with a central core based on a 4,6‐dichloro‐1,3‐phenylene group were synthesized by varying the terminal chains (R = OC₁₀H₂₁ or OC₁₁H₂₁) and the lateral substituents (X = H, F or Cl). Their mesophases were characterized by a combination of differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X‐ray diffractometry. Mesomorphic properties of the banana‐shaped mesogens with an olefinic group (R = OC₁₁H₂₁) as a terminal chain are sensitive to lateral halogen substituents as much as those of the analogues with a saturated group (R = OC₁₀H₂₁). The compounds with X = F showed an antiferroelectric switchable smectic phase, which has been designated a B₂ phase. The compounds without a lateral halogen substituent only formed a nematic phase, while the compounds with X = Cl did not exhibit a mesophase in the melt.     

A Perylene Bisimide Cyclophane as a “Turn‐On” and “Turn‐Off” Fluorescence Probe

A rigid, covalently linked perylene‐3,4:9,10‐tetracarboxylic acid bisimide (PBI) cyclophane was synthesized by imidization of a bay‐substituted perylene bisanhydride with p‐xylylenediamine. The interchromophoric distance of approximately 6.5 Å establishes an ideal rigid cavity for the encapsulation of large aromatic compounds such as perylene and anthracene with binding constants up to 4.6×10⁴ M ^?1 (in CHCl₃). For electron‐poor guest molecules, the complexation process is accompanied by a significantly increased fluorescence, whereas the emission intensity is dramatically quenched by more electron‐rich guests because of the formation of charge‐transfer complexes. Furthermore, the influence of the PBI core twist on the binding constant results in a remarkable selectivity towards more flexible aromatic guest molecules.     

Regioselective Functionalization of Core‐Persubstituted Perylene Diimides

Regioselective functionalization of core per‐substituted perylene diimides has been achieved efficiently based on a new versatile building block, named tetrabromotetrachloro‐perylene‐3,4:9,10‐tetracarboxylic acid dianhydride (Br₄Cl₄‐PTCDA), which affords a series of novel chromophores with impressive optoelectronic properties. Direct palladium‐catalyzed fourfold intramolecular ring fusion affords successfully unique propeller‐shaped biscarbazole[2,3‐b]carbazole diimides with six annulated rings.     

Synthesis and Solid State Properties of Novel Fluorescent Polyester Star Polymers

Two novel tetra‐ and hexahydroxy functionalized perylene chromophores have been used as initiators for the Sn(oct)₂ catalyzed ring‐opening polymerization of different lactones. The arms of the resulting star polymers were comprised of either crystallizable poly(L ‐lactide) or poly(ε‐caprolactone) arms or of amorphous poly[γ‐(tert‐amyl)‐ε‐caprolactone] chains. The star polymers were investigated by differential scanning calorimetry, X‐ray scattering and dynamic mechanical and optical spectroscopy. Whereas the thermal properties of the poly(ε‐caprolactone) stars were barely affected by the star topology, crystallization of the poly(L ‐lactide) stars was strongly hindered by the star‐shaped architecture. Interestingly, for the amorphous poly[γ‐(tert‐amyl)‐ε‐caprolactone] stars a decrease in T_g with increasing chain length was found, reflecting the declining influence of the rigid perylene core on segmental mobility with increasing arm length. While the solid state and solution optical properties of high molar mass polyester stars were identical, the excitation and fluorescence emission spectra of spin‐coated films of the low molecular weight polymers revealed a red shift, pointing towards perylene – perylene interactions in these samples. The optical spectroscopy experiments suggested that arm length, rather than the number of arms, is the most important parameter determining encapsulation and preventing aggregation of the perylene core moieties in the solid state.

     

Direct Evidence of Significantly Different Chemical Behavior and Excited‐State Dynamics of 1,7‐ and 1,6‐Regioisomers of Pyrrolidinyl‐Substituted Perylene Diimide

Novel bay‐functionalized perylene diimides with additional substitution sites close to the perylene core have been prepared by the reaction between 1,7(6)‐dibromoperylene diimide 6 (dibromo‐PDI) and 2‐(benzyloxymethyl)pyrrolidine 5 . Distinct differences in the chemical behaviors of the 1,7‐ and 1,6‐regioisomers have been discerned. While the 1,6‐dibromo‐PDI produced the corresponding 1,6‐bis‐substituted derivative more efficiently, the 1,7‐dibromo‐PDI underwent predominant mono‐debromination, yielding a mono‐substituted PDI along with a small amount of the corresponding 1,7‐bis‐substituted compound. By varying the reaction conditions, a controlled stepwise bis‐substitution of the bromo substituents was also achieved, allowing the direct synthesis of asymmetrical 1,6‐ and 1,7‐PDIs. The compounds were isolated as individual regioisomers. Fullerene (C₆₀) was then covalently linked at the bay region of the newly prepared PDIs. In this way, two separate sets of perylene diimide–fullerene dyads, namely single‐bridged (SB‐1,7‐PDI‐C₆₀ and SB‐1,6‐PDI‐C₆₀) and double‐bridged (DB‐1,7‐PDI‐C₆₀ and DB‐1,6‐PDI‐C₆₀), were synthesized. The fullerene was intentionally attached at the bay region of the PDI to achieve close proximity of the two chromophores and to ensure an efficient photoinduced electron transfer. A detailed study of the photodynamics has revealed that photoinduced electron transfer from the perylene diimide chromophore to the fullerene occurs in all four dyads in polar benzonitrile, and also occurs in the single‐bridged dyads in nonpolar toluene. The process was found to be substantially faster and more efficient in the dyads containing the 1,7‐regioisomer, both for the singly‐ and double‐bridged molecules. In the case of the single‐bridged dyads, SB‐1,7‐PDI‐C₆₀ and SB‐1,6‐PDI‐C₆₀, different relaxation pathways of their charge‐separated states have been discovered. To the best of our knowledge, this is the first observation of photoinduced electron transfer in PDI‐C₆₀ dyads in a nonpolar medium.     

Practical synthesis of perylene-monoimide building blocks that possess features appropriate for use in porphyrin-based light-harvesting arrays

Perylene-monoimide dyes with solubilizing aryloxy substituents at the perylene perimeter and a synthetic handle on the N-aryl group are valuable building blocks for incorporation as accessory pigments in porphyrin-based light-harvesting arrays. A family of such dyes has been prepared by reaction of 1,6,9-tris(4-tert-butylphenoxy)perylene-3,4-dicarboxylic anhydride with a set of 4-iodo/ethynyl anilines (with or without 2,6-diisopropyl substituents) in the presence of Zn(OAc)₂·2H₂O in imidazole/mesitylene at 130°C. The workup procedures throughout the synthesis have been streamlined for scale-up purposes, minimizing chromatography. Two bis(perylene)porphyrin building blocks were prepared in a rational manner and examined in Sonogashira and Glaser polymerizations. The two isopropyl groups on the N-aryl group and the three 4-tert-butylphenoxy groups at the perylene perimeter are essential for high solubility of the bis(perylene)porphyrins and corresponding oligomers in organic solvents.