A set of Pd(II) biladiene complexes bearing different combinations of methyl-and phenyl-substituents on the sp 3 -hybridized meso-carbon (the 10-position of the biladiene framework) was prepared and studied. In addition to a previously described Pd(II) biladiene complex bearing geminal dimethyl substituents a the 10-position (Pd[DMBil]), homologous Pd(II) biladienes bearing geminal methyl and phenyl substituents (Pd[MPBil1]) and geminal diphenyl groups-(Pd[DPBil1]) were prepared and structurally characterized. Detailed electrochemical as well as steady-state and time-resolved spectroscopic experiments were undertaken to evaluate the influence of the substituents on the biladiene's tetrahedral meso-carbon. Although all three biladiene homologues are isostructural, Pd[MPBil1] and Pd[DPBil1] display more intense absorption profiles that shift slightly toward lower energies as geminal methyl groups are replaced by phenyl rings. All three biladiene homologues support a triplet photochemistry, and replacement of the geminal dimethyl substituents of Pd[DMBil1] (Φ Δ = 54%) with phenyl groups improves the ability of Pd[MPBil1] (Φ Δ = 76%) and Pd[DPBil1] (Φ Δ = 66%) to sensitize 1 O 2 . Analysis of the excited-state dynamics of the Pd(II) biladienes by transient absorption spectroscopy shows that each complex supports a long-lived triplet excited-state (i.e., τ > 15 μs for each homologue) but that the ISC quantum yields (Φ T ) varied as a function of biladiene substitution. The observed trend in ISC efficiency matches that for singlet oxygen sensitization quantum yields (Φ Δ ) across the biladiene series considered in this work. The results of this study provide new insights to guide future development of biladiene based agents for PDT and other photochemical applications.

Room-temperature I–V characteristics of epitaxially grown Si/SiGe resonant interband tunneling diodes (RITDs) with extremely high peak current densities are presented. By optimizing the physical design, doping concentrations, and post-growth anneal temperatures, RITDs having peak current densities over 150 kA/cm2, peak-to-valley current ratios (PVCRs) greater than 2, and an estimated speed index of 34 mV/ps have been obtained. The interplay among the conditions to achieve maximum current density and highest PVCR is discussed. This result demonstrates the high potential of this type of Si-based tunnel diode for high-power mixed-signal applications.

Photodynamic therapy (PDT), which involves the photoinduced sensitization of singlet oxygen, is an attractive treatment for certain types of cancer. The development of new photochemotherapeutic agents remains an important area of research. Macrocyclic tetrapyrrole compounds including porphyrins, phthalocyanines, chlorins, and bacteriochlorins have been pursued as sensitizers of singlet oxygen for PDT applications but historically are difficult to prepare/purify and can also suffer from high nonspecific dark toxicity, poor solubility in biological media, and/or slow clearance from biological tissues. In response to these shortcomings, we have developed a series of novel linear tetrapyrrole architectures complexed to late transition metals as potential PDT agents. We find that these dimethylbiladiene (DMBil1) tetrapyrrole complexes can efficiently photosensitize generation of 1 O 2 oxygen upon irradiation with visible light. To extend the absorption profile of the DMBil1 platform, alkynyl−aryl groups have been conjugated to the periphery of the tetrapyrrole using Sonogashira methods. Derivatives of this type containing ancillary phenyl (DMBil−PE), naphthyl (DMBil−NE), and anthracenyl (DMBil−AE) groups have been prepared and characterized. In addition to structurally characterizing Pd[DMBil−NE] and Pd[DMBil−AE], we find that extension of the tetrapyrrole conjugation successfully red-shifts the absorption of the DMBil−Ar family of biladienes further into the phototherapeutic window (i.e., 600−900 nm). Photochemical sensitization studies demonstrate that our series of new palladium biladiene complexes (Pd[DMBil−Ar]) can sensitize the formation of 1 O 2 with quantum yields in the range Φ Δ = 0.59−0.73 upon irradiation with light of λ ≥ 650 nm. The improved absorption properties of the Pd[DMBil−Ar] complexes in the phototherapeutic window, together with their high 1 O 2 quantum yields, highlight the promise of these compounds as potential agents for PDT.

Deep-level transient spectroscopy measurements were performed in order to investigate the effects of substrate growth temperature and dopant species on deep levels in Si layers during low-temperature molecular beam epitaxial growth. The structures studied were n ϩ-p junctions using B doping for the p layer and p ϩ-n junctions using P doping for the n layer. While the density of hole traps H1 ͑0.38-0.41 eV͒ in the B-doped p layers showed a clear increase with decreasing growth temperature from 600 to 370°C, the electron trap density was relatively constant. Interestingly, the minority carrier electron traps E1 ͑0.42-0.45 eV͒ and E2 ͑0.257 eV͒, found in the B-doped p layers, are similar to the majority carrier electron traps E11 ͑0.48 eV͒ and E22 ͑0.269 eV͒ observed in P-doped n layers grown at 600°C. It is hypothesized that these dominating electron traps are associated with pure divacancy defects and are independent of the dopant species.

Photodynamic therapy (PDT) is a promising treatment option that ablates cancerous cells and tumors via photoinduced sensitization of singlet oxygen. Over the last few decades, much work has been devoted to the development of new photochemotherapeutic agents for PDT. A wide variety of macrocyclic tetrapyrrole based photosensitizers have been designed, synthesized and characterized as PDT agents. Many of these complexes have a variety of issues that pose a barrier to their use in humans, including biocompatibility, inherent toxicity, and synthetic hurdles. We have developed a non-traditional, non-cyclic, and non-aromatic tetrapyrrole ligand scaffold, called the biladiene (DMBil1), as an alternative to these traditional photosensitizer complexes. Upon insertion of a heavy atom such as Pd2+ center, Pd[DMBil1] generates singlet oxygen in substantial yields (ΦΔ = 0.54, λexc = 500 nm) when irradiated with visible light. To extend the absorption profile for Pd[DMBil1] deeper into the phototherapeutic window, the tetrapyrrole was conjugated with alkynyl phenyl groups at the 2- and 18-positions (Pd[DMBil2-PE]) resulting in a significant redshift while also increasing singlet oxygen generation (ΦΔ = 0.59, 600 nm). To further modify the dialkynyl-biladiene scaffold, we conjugated a 1,8-diethynylanthracene with to the Pd[DMBil1] tetrapyrrole in order to further extend the compound’s π-conjugation in a cyclic loop that spans the entire tetrapyrrole unit. This new compound (Pd[DMBil2-P61]) is structurally reminiscent of the P61 Black Widow aircraft and absorbs light into the phototherapeutic window (600–900 nm). In addition to detailing the solid-state structure and steady-state spectroscopic properties for this new biladiene, photochemical sensitization studies demonstrated that Pd[DMBil2-P61] can sensitize the formation of 1O2 with quantum yields of ΦΔ = 0.84 upon irradiation with light λ = 600 nm. These results distinguish the Pd[DMBil2-P61] platform as the most efficient biladiene-based singlet oxygen photosensitizer developed to date. When taken together, the improved absorption in the phototherapeutic window and high singlet oxygen sensitization efficiency of Pd[DMBil2-P61] mark this compound as a promising candidate for future study as an agent of photodynamic cancer therapy.