Exploring the photoexcited triplet states of aluminum and tin corroles by time-resolved Q-band EPR

The photoexcited triplet states of three 5,10, 15-tris(pentafluorophenyl)corroles (tpfc), hosting Sn(IV) and Al(III) in their core, namely, Sn(Cl)(tpfc), Al(pyr)₂(tpfc) and Al(pyr)₂(tpfc-Br₈), were studied by time-resolved electron paramagnetic resonance (TREPR) spectroscopy in the nematic liquid crystal E7. Only two of these metallocorroles, namely, Sn(Cl)(tpfc) and Al(pyr)₂(tpfc-Br₈), exhibit TREPR spectra following pulsed laser excitation. This result is rationalized in terms of a very low quantum yield of triplet formation in Al(pyr)₂(tpfc). Analysis of the spin polarized Q-band (34 GHz) EPR spectra of Sn(Cl)(tpfc) and Al(pyr)₂(tpfc-Br₈) provides detailed information on the magnetic and kinetic parameters of the triplet states as well as on the molecular ordering of the complexes in the liquid crystal. With the assignment of the zero-field splitting parameterD<0 for the Sn(Cl)(tpfc) and Al(pyr)₂(tpfc-Br₈), one can evaluate the dominant intersystem crossing path for these metallocorroles. Analysis reveals that in Sn(Cl)(tpfc) the in-plane triplet sublevels are preferentially populated, i.e.,A _X, A_Y?A _Z. This can be rationalized in terms of weak electronic interactions between the Sn(IV) ion and the corrole π-system, consistent with the domed structure of Sn(Cl)(tpfc). In Al(pyr)₂(tpfc-Br₈), however, the out-of-plane triplet sublevel is predominantly populated, i.e.,A _Z>A _X, A_Y, which is attributed to a large increase in the spin-orbit coupling strength arising from the peripheral bromine atoms on the corrole skeleton.     

Silver compounds in synthetic chemistry : Part 4. 4-Tetrafluoropyridyl silver(I), AgC5F4N in redox transmetallations—possibilities and limitations in reactions with group 15 elements

While reactions of AgC₅F₄N with elemental arsenic, antimony, and bismuth proceed selectively yielding E(C₅F₄N)₃ (E = As, Sb, Bi), those with white and red phosphorus remained obscure giving product mixtures of so far unknown stoichiometry. The phosphorus compound was therefore prepared by an alternative route. P(C₅F₄N)₃ and As(C₅F₄N)₃ crystallize isostructurally in the monoclinic space group P2₁/c (no. 14) with four molecules per unit cell. π-π Offset stacking together with edge-face stacking lead to dimeric units which are connected by a second edge-face stacking of nitrogen onto the opposite side of the same tetrafluoropyridyl ring extending the structure into infinite chains.     

Letters to the Editor

The mathematical intelligencer encourages comments about the material in this issue. letters to the editor should be sent to either of the editors-in-chief, chandler davis or Marjorie Senechal.     

Optical parametric oscillator with a pulse repetition rate of 39 GHz and 2.1-W signal average output power in the spectral region near 1.5 microm

We present a singly resonant, synchronously pumped optical parametric oscillator with a record-high repetition rate of 39 GHz. The transform-limited 2.2-ps pulses at 1570 nm have as much as 2.1-W average output power. The all-solid-state pump source is based on a diode-pumped passively mode-locked 39-GHz Nd:YVO4 laser and an efficient ytterbium-doped fiber amplifier.     

Exponential decay of derivatives of covariance operators on the lattice

We prove exponential decay for derivatives of covariance operators on the lattice. This result is obtained by using random walk methods on the v-dimensional lattice and a certain estimate on the generating function of the one-dimensional random walk. The result is useful in the frame of the cluster and mean field expansion of continuous spin models on the lattice.