Optical properties neutral

The synthesis of new materials having novel electronic or optical properties is of great current interest. One approach to the synthesis of such materials is to systematically link small sandwich units together to form an extended multi-decker sandwich system. Immediately following the discovery of the triple-decker structure of the Cp3Ni2+ complex in early 1970s,181 Grimes and co-workers synthesized the first neutral triple-decker metallacarborane sandwich compound. Most of the subsequent research in this field, some of which has been described... 

Chow C-F, Fuji S, Lehn J-M. Metallodynamers neutral dynamic metallosupramolecular polymers displaying transformation of mechanical and optical properties on constitutional exchange. Angew Chem Int Ed 2007 46 5007 -5010. 

Photometric accuracy is determined by comparing the difference between the measured absorbance of the reference standard materials and the established standard value. Many solid and liquid standards are commonly used to verify the photometric accuracy of a spectrophotometer. An optically neutral material with little wavelength dependency for its transmittance/absorbance is desirable because it eliminates the spectral bandwidth dependency of measurements. The advantages and disadvantages of various commonly used photometric accuracy standards are summarized in Table 10.6. Even for a relatively stable reference standard, the intrinsic optical properties may change over time. Recertification at regular intervals is required to ensure that the certified values of the standards are meaningful and accurate for the intended use. 

Pt acts like a neutral density filter through a wide wavelength range and can be used in the UV when the film is on quartz. Au has an optical window with maximum transmission at 540 nm. On quartz, Au can also be used in the UV when the conductivity is comparable to Pt. For the visible region, Au films with good transmission and with resistance as low as a few ohms per square can be prepared. Typical optical properties are shown in Figure 11.3 [55]. The electrochemical properties are similar to bulk Pt and Au, as seen in Figure 11.5 [74],... 

When an analyte lacks measurable optical properties by itself, spectroscopically active intermediate molecules are needed. Indicators modify their optical properties when they interact with the analyte and usually are neutral or ionizable dyes. 

A dozen years ago, the optical properties of a very few cases of Ir(III) complexes were known [1,2]. In the same period, Ru(II)-, Os(II)- and Re(I)-polyimine complexes, for instance, were comparatively much more popular as a consequence of research efforts related to the theme of the interconversion between light and chemical energy [3-5]. In early times, the tricationic Ir(bpy)33+ species proved difficult to prepare, and was clearly identified only after closely related species were studied [ 1,6,7] bpy is 2,2 -bipyridine, Fig. 1. At the same time, the neutral/ac-Ir(ppy)3 species initially appeared as a side-product of dichloro-bridged dimers of the type [Ir(ppy)2Cl]2 [8] ppy is the cyclometalating anion from Hppy, Fig. 1. Today, we witness an impressive expansion of the literature on the luminescence of Ir(III) complexes, as illustrated by Fig. 2. 

Terpyridine, N N N ligands (245-249) and their N C N and N N C analogues (250-257) have been successfully coordinated to Pt(II), leading to neutral, mono- or doubly charged species, which in some cases display bright luminescence, both in degassed fluid solutions and frozen matrices. In particular, it has been shown by Che et al. that they can form supramolecular structures, such as nanowires, nanosheets, and polymeric mesophases, with interesting optical properties (214—216,258). 

---