2,2′:3′,2′′‐Terthiophene‐Based all‐Thiophene Dendrons and Dendrimers: Synthesis,Structural Characterization,and Properties

The synthesis of generational dendritic oligothiophenes (DOTs) has been successfully achieved by a divergent/convergent approach that involves halogenation, boronation, and palladium‐catalyzed Suzuki coupling reactions. The key point in the presented synthetic approach is the use of trimethylsilyl (TMS) protecting groups, which allow for the core‐lithiation and subsequent boronation of the dendrons and for the peripheral ipso‐substitution with iodine monochloride or N‐bromosuccimide. In addition, the TMS protecting groups can be completely removed by using tetrabutylammonium fluoride, thus yielding only‐thiophene‐based dendrons and dendrimers. Due to their highly branched structure, all these synthesized DOTs are soluble in organic solvents. Chemical structures were confirmed by NMR spectroscopic, mass spectrometric, and elemental analysis. Concentration‐dependent ¹H NMR spectroscopic investigations revealed that the higher generation compounds tend to aggregate in solution. Such an aggregation behavior was further confirmed by measuring with MALDI‐TOF MS. Both MALDI‐TOF MS and gel‐permeation chromatography (GPC) analyses confirmed the monodispersity of the DOTs. Furthermore, GPC results revealed that these DOT molecules adopt a condensed globular molecular shape. Their optical and electronic properties were also investigated. The results indicated that these DOTs comprise various conjugated α‐oligothiophenes with different chain lengths, which results in the higher generation compounds showing broad and featureless UV/Vis absorption spectra and ill‐defined redox waves.     

Tetrathiafulvalene‐Fused Porphyrins via Quinoxaline Linkers: Symmetric and Asymmetric Donor–Acceptor Systems

A tetrathiafulvalene (TTF) donor is annulated to porphyrins (P) via quinoxaline linkers to form novel symmetric P–TTF–P triads 1 a – c and asymmetric P–TTF dyads 2 a , b in good yields. These planar and extended π‐conjugated molecules absorb light over a wide region of the UV/Vis spectrum as a result of additional charge‐transfer excitations within the donor–acceptor assemblies. Quantum‐chemical calculations elucidate the nature of the electronically excited states. The compounds are electrochemically amphoteric and primarily exhibit low oxidation potentials. Cyclic voltammetric and spectroelectrochemical studies allow differentiation between the TTF and porphyrin sites with respect to the multiple redox processes occurring within these molecular assemblies. Transient absorption measurements give insight into the excited‐state events and deliver corresponding kinetic data. Femtosecond transient absorption spectra in benzonitrile may suggest the occurrence of fast charge separation from TTF to porphyrin in dyads 2 a , b but not in triads 1 a – c . Clear evidence for a photoinduced and relatively long lived charge‐separated state (385 ps lifetime) is obtained for a supramolecular coordination compound built from the ZnP–TTF dyad and a pyridine‐functionalized C₆₀ acceptor unit. This specific excited state results in a (ZnP–TTF)^?+ ??? (C₆₀py)^?? state. The binding constant of Zn^II ??? py is evaluated by constructing a Benesi–Hildebrand plot based on fluorescence data. This plot yields a binding constant K of 7.20×10⁴ M ^?1, which is remarkably high for bonding of pyridine to ZnP.     

Charge carrier mobility,photovoltaic, and electroluminescent properties of anthracene‐based conjugated polymers bearing randomly distributed side chains

This article reports on the synthesis, characterization, and properties of various anthracene‐containing poly (p‐phenylene‐ethynylene)‐alt‐poly(p‐phenylene‐vinylene) (PPE‐PPV) polymers (AnE‐PVs) bearing statistical distributions of various side chains. Primarily, the ratio of linear octyloxy and branched 2‐ethylhexyloxy side chains at the poly(p‐phenylene vinylene) (PPV) parts was varied, leading to the polymers stat, stat1, and stat2. Furthermore, polymers also containing asymmetric substituted PPV and poly(p‐phenylene ethynylene) units (bearing methoxy and 2‐ethylhexyloxy side chains) were prepared yielding stat3, stat4, and stat5. These materials exhibit a broad variation in their photovoltaic properties. It is once more shown that side chains and their distribution can crucially affect the photovoltaic device performance. The introduction of units with asymmetric substitution into these systems seems to be harmful for their utilization in photovoltaic applications. Organic field‐effect transistors were fabricated to investigate hole mobilities in these new materials. Large variance was observed, falling in the range of almost two orders of magnitude, indicating rather different π–π stacking behavior of the polymer backbones owing to side‐chain modifications. Moreover, a selection of the new polymeric systems was investigated regarding their potential for light‐emitting diode (LED) applications. Polymer LEDs using the polymers AnE‐PVstat, ‐stat3, ‐stat4, and ‐stat5, as the active layer showed turn‐on voltage of ～2 V and exhibited red light emission. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

TTF-porphyrin dyads as novel photoinduced electron transfer systems

A TTF-linked porphyrin dyad and its zinc complex have been synthesized as novel photosystems with a redox-active pendant. The two chromophores of these dyads are not interactive in the absorption spectra, but the fluorescence of the porphyrin chromophore is dramatically quenched by intramolecular electron transfer from the TTF pendant.     

Highly luminescent diyne (?CC?CC?) containing hybrid polyphenyleneethynylene/poly(p‐phenylenevinylene) polymer: Synthesis and characterization

Luminophoric dialdehyde 1,4‐bis[4‐formylphenylethynyl‐(2,5‐dioctadecyloxyphenyl)‐buta‐1,3‐diyne] ( 4 ) enables the synthesis of diyne‐containing hybrid polyphenyleneethynylene/poly(p‐phenylenevinylene) polymer poly[1,4‐phenylene‐ethynylene‐1,4‐(2,5‐dioctadecyloxy)phenylene‐butadi‐1,3‐ynylene‐1,4‐(2,5‐dioctadecyloxy)phenylene‐ethynylene‐1,4‐phenylene‐ethene‐1,2‐diyl‐1,4‐(2,5‐dioctadecyloxy)phenylene‐ethene‐1,2‐diyl] ( 7 ) with a well‐defined general structure (? Ph? C?C? Ar? C?C? C?C? Ar? C?C? Ph? CH?CH? Ar? CH?CH? )_n, which was confirmed by NMR and infrared spectroscopy. The highly luminescent material is thermostable, soluble in usual organic solvents through the grafting of octadecyloxy side groups, and can be processed into transparent films. With the aim to investigate the effect of ? C?C? C?C? in the photophysical behavior of 7 , a comparison of the photophysics of monomers 3 [1,4‐bis(4‐formylphenylethynyl)‐2,5‐dioctadecyloxybenzene] and 4 and subsequently of their respective polymers 6 and 7 has been carried out. Similar photophysical behaviors for 6 (poly[1,4‐phenylenethynylene‐1,4‐(2,5‐dioctadecyloxyphenylene)ethene‐1,2‐diyl]) and 7 were observed in dilute CHCl₃ solution as a result of an identical chromophore system responsible for the absorption (λ_a = 448 nm) and emission (λ_f = 490 nm) in both compounds. The increased planarization and enhanced rigidity of the conjugated backbone in the solid state at room temperature as well as in frozen dilute tetrahydrofuran solution at 77 K cause the bathochromic shift of the absorption and emission spectra. The large octadecyloxy side chains obviously limit strong π‐π interchain interactions in the solid films, which explains the high fluorescence quantum yields of 35 and 52% obtained for 6 and 7 , respectively. The energetically arduous migration of the π electron through the diyne units not only requires a higher threshold voltage for the detection of photoconductivity in 7 but could possibly limit radiationless deactivation channels of the exciton, which explains the approximate 20% fluorescence quantum yields difference between 6 and 7 in the solid state. The electron‐withdrawing effect of the triple bonds confer both 6 and 7 with a good electron‐accepting property (E^ox = 1.39 V vs Ag/AgCl) if used in light‐emitting diode devices. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2670–2679, 2002     

Synthesis and Chiroptical Properties of Chiral Carbazole-Based BODIPYs

A series of carbazole-based boron dipyrromethenes (BODIPYs) 2 a – g bearing binaphthyl units have been synthesized by the Et₂AlCl-mediated reaction of the corresponding BODIPY difluorides 1 a – g with 1,1′-binaphthalene-2,2′-diol. Substituents such as halogen, nitrile, and amino groups were tolerated under the reaction conditions, and the reaction of the phenylethynyl-substituted 1 h gave (R,R)- 3 h bearing two binaphthyl units. The chiroptical properties of these dyes with different substituents were investigated by UV/Vis, CD, fluorescence, and circularly polarized luminescence (CPL) spectroscopy. The CD spectra showed Cotton effects in the absorption region of the BODIPY moieties. In addition, they showed CPL both in solution and in the solid state. Interestingly, several dyes recorded higher g_lum values in the solid state, probably due to intermolecular interactions. Because (R,R)- 3 h recorded relatively low g_lum values, the diastereomer (R,S)- 3 h was prepared. The (R,S) diastereomer showed intense CPL, which suggests a synergetic effect of the two binaphthyl groups. Finally, chiral carbazole-based BODIPY dimers have been synthesized for the first time and their chiroptical properties were investigated. They showed redshifted fluorescence and CPL, which reached the near-IR (NIR) region in the solid state.