STUDIES ON PLANT BILE PIGMENTS

The reaction of bilirubins with aromatic diazonium salts in alcoholic solvents leads to an equimolar mixture of two types of products. One is the well-known 9-azopyrromethenone. The other is a yellow product (A,,, z 420nm) identified as 9-alkoxymethylpyrromethenone. the alkoxy-substituent being derived from the solvent. Thus, reaction of the symmetrically substituted bilirubins llla (lc) and XIIIJ (lb) in methanol with diazotized sulfanilic acid yields one mole of the azopigments (4b and 4a). respectively, and one mole of the corresponding 9-methoxymethylpyrromethcnones (2b and 2a). Bilirubin IXa (la) consequently yields a mixture of all four products. The two resulting 9-methoxymethylpyrromethenoncs were separated by chromatography and identified as 2a and 2b. They can react further with the dia7onium salts lo give the corresponding 9-aznpyrromethenones, but the reaction is much slower than that of bilirubin. which explains the observed product distribution. These results are discussed in relation to earlier work. ALMOST a hundred years ag

Photo-FETs: phototransistors enabled by 2D and 0D nanomaterials

The large diversity of applications in our daily lives that rely on photodetection technology requires photodetectors with distinct properties. The choice of an adequate photodetecting system depends on its application, where aspects such as spectral selectivity, speed, and sensitivity play a critical role. High-sensitivity photodetection covering a large spectral range from the UV to IR is dominated by photodiodes. To overcome existing limitations in sensitivity and cost of state-of-the-art systems, new device architectures and material systems are needed with low-cost fabrication and high performance. Low-dimensional nanomaterials (0D, 1D, 2D) are promising candidates with many unique electrical and optical properties and additional functionalities such as flexibility and transparency. In this Perspective, the physical mechanism of photo-FETs (field-effect transistors) is described and recent advances in the field of low-dimensional photo-FETs and hybrids thereof are discussed. Several requirements for the channel material are addressed in view of the photon absorption and carrier transport process, and a fundamental trade-off between them is pointed out for single-material-based devices. We further clarify how hybrid devices, consisting of an ultrathin channel sensitized with strongly absorbing semiconductors, can circumvent these limitations and lead to a new generation of highly sensitive photodetectors. Recent advances in the development of sensitized low-dimensional photo-FETs are discussed, and several promising future directions for their application in high-sensitivity photodetection are proposed.Peer ReviewedPostprint (author's final draft