No abstract

The concept of panchromatic light harvesting, that is, broad absorption cross sections throughout most of the visible range and excited state funnelling, has been realized in a novel set of porphyrazines. On one hand, zinc, copper, or magnesium ions were complexed by porphyrazines to tune their ground and excited state features. On the other hand, up to eight Bodipys were covalently attached to the periphery of the porphyrazines to enhance the ground state absorption. The corresponding star-shaped conjugates were probed by advanced photophysical measurements, that is, time-resolved fluorescence and femtosecond transient absorption spectroscopy. From the latter we derive spectroscopic and kinetic evidence in support of a fast and unidirectional energy transfer from the photoexcited Bodipy at the periphery to the porphyrazine at the core. In addition, the impact of the different metal centers is demonstrated.

We have performed the syntheses of a novel pyrene-porphyrazine conjugate (ZnPzPy) and a reference porphyrazine (ZnPz) to promote the wet-chemical exfoliation of graphite based on the synergetic use of ultrasonication, centrifugation, and doping. ZnPzPy features, on one hand, a hydrophobic pyrene to anchor onto the basal plane of graphene, and, on the other hand, an amphoteric porphyrazine to either p- or n-dope graphene. To this end, we have characterized individual building blocks, that is, ZnPzPy and exfoliated graphite, and the resulting electron donor-acceptor nanohybrid, that is, ZnPzPy/graphene (ZnPzPy-G), by means of an arsenal of microscopic and spectroscopic techniques. From a full-fledged characterization we conclude that ZnPzPy facilitates the exfoliation of graphite affording suspensions featuring 9.5% of single- or few-layered ZnPzPy-G with a mean average size of 200 ± 140 nm. Importantly, a notable shift of charge density from graphene to ZnPzPy in the ground state of ZnPzPy-G corroborates the preference of exfoliated graphite to undergo p-doping rather than n-doping. As an immediate consequence, a full charge separation leads in the excited state to a 750 ± 150 ps lived charge separated state.

Supporting Information General Methods. Unless otherwise stated, all starting materials were purchased from commercial suppliers and used without further purification. THF was freshly distilled from sodium benzophenone ketyl; toluene, diisopropylamine, and (trimethylsilyl)acetylene were distilled from CaH 2 ; bis(trimethylsilyl)acetylene and CpCo(CO) 2 were vacuum transferred immediately before use. All reactions involving airor moisture-sensitive materials were carried out under an atmosphere of dry nitrogen or argon with oven-or flame-dried glassware. In experiments requiring slow addition of reagents, NORM-JECT single-use syringes were used, mounted on a Sage Instruments single syringe pump. The light source used in cycloaddition reactions employing CpCo(CO) 2 was a 300 W tungsten halogen slide projector lamp with an applied potential of 60-70 V positioned 3-5 cm from the flask. Analytical thin-layer chromatography (TLC) was performed on Merck silica gel 60 F254 plates. Flash chromatography was executed on silica gel (60-200 or 230-400 mesh) from Sorbent Technologies, preparative thin-layer chromatography on silica gel GF Uniplates (UV254, 1000 microns) from Analtech. NMR spectra were recorded on Bruker AVQ400 (400 MHz), AV500 (500 MHz), or AV600 (600 MHz) instruments. Multiplicity is described by the abbreviations s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet. Chemical shifts are given in ppm. 1 H NMR spectra were referenced to the residual solvent peaks at δ = 7.26 (CDCl 3) or 5.32 ppm (CD 2 Cl 2). 13 C NMR spectra were referenced to the solvent peaks at δ = 77.0 (CDCl 3), 54.0 (CD 2 Cl 2), and 128.39 ppm (benzene). Infrared spectra were obtained on Thermo Nicolet, Avatar 370, or Perkin Elmer Spectrum 100 FT-IR spectrometers, respectively, and are reported in wavenumbers (cm-1). UV/Vis spectra were obtained on either a Hewlett-Packard HP 8453 UV-Vis ChemStation, a Perkin Elmer Lambda 35 spectrometer, or a Varian 50 Bio UV/Vis