Luminescence thermochromism

The trinuclear complexes [Au3(/7-MeC6H4N = OEt)3] and [Au3(Bzim)3] (Bzim= 1-benzylimida-zolate), which are colorless, can produce brightly colored materials by sandwiching naked Ag+ or Tl+ ions form linear-chain complexes (Figure 27) with luminescence properties as luminescence thermochromism.3173,3174... 

A monoclinic form of the Cu iodide pyridine complex has been prepared but unlike the cubane tetrameric modification, this isomer does not show luminescence thermochromism. The photochemistry of copper(n) chloride has been examined at 313 nm and 77 K in ethanol and HCl solution and has shown transient radical complex formation between Cu and CH3CHOH. Photolysis of DMF solutions of [CuClJ " is reported to lead to formation of the radical,CH2(CH3)NCHO, (10) and the Cu -(10) complex. At higher concentrations of [CuClJ ", photooxidation of (10) by excited [CuClJ predominates. The photochemistry of the... 

The above properties (a and b) are interpreted by Cohen and Schmidt (21) on the basis of a detailed crystallographic study of photochromic and thermochromic anils. They conclude that photochromic crystals involve structures in which the central portion of adjacent molecules are essentially isolated from one another, so that, to a first approximation the energetics are that of an isolated molecule. On the other hand, when the alignment of the molecular dipoles is such as to give strong intermolecular interactions then the transition to the quinoid form requires much less energy and can occur thermally. For crystals in which thermochromism occurs, the photochemical isomerization is still possible but the reverse reaction is so rapid that no buildup of color is observed. In fact, fluorescence measurements on the thermochromic 5 -chlorosalicylidene-aniline (Fig. 5) indicate that photochemical isomerization precedes the luminescence process via the photochromic route ... 

Abstract We describe mechanochromic and thermochromic photoluminescent liquid crystals. In particular, mechanochromic photoluminescent liquid crystals found recently, which are new stimuli-responsive materials are reported. For example, photoluminescent liquid crystals having bulky dendritic moieties with long alkyl chains change their photoluminescent colors by mechanical stimuli associated with isothermal phase transitions. The photoluminescent properties of molecular assemblies depend on their assembled structures. Therefore, controlling the structures of molecular assemblies with external stimuli leads to the development of stimuli-responsive luminescent materials. Mechanochromic photoluminescent properties are also observed for a photoluminescent metallomesogen and a liquid-crystalline polymer. We also show thermochromic photoluminescent liquid crystals based on origo-(/ -phenylenevinylene) and anthracene moieties and a thermochromic photoluminescent metallocomplex. 

The luminescent binuclear gold dithiophosphate complexes [Au2 S2P-(OR)2h] (R = Me, Et) were found to possess comparable intra- and intermolecular aurophilic contacts and afforded one-dimensional Au - Au chain structures [60]. At 77 K, solid samples of [Au2 S2P(OMe)2 2] displayed multiple emission bands, with the two concentration-dependent higher energy bands at 415 nm (r = 20 ns) and 456 nm (r = 2.16 is) assigned to XMC and 3MC emission, respectively, while the lower energy band at 560 nm was attributed to a LMCT excited state. [Au2 S2P(OR)2 2] was further shown to exhibit intense luminescence of different colors and striking thermochromism of the emission in frozen glasses of different solvents. 

It is interesting that the emission of the complex is thermochromic and thus the temperature influences emission energies and lifetimes. For instance, two bands at 575 and 518 nm appear at 5 K, but at 300 K the former disappear when temperature increases. This was attributed to luminescent traps. In contrast, the most energetic band shifts to blue under the same conditions it appears at 509 at 40 K and at 483 nm at 360 K. 

In addition, the optical properties of these materials, which include luminescence and thermochromism, are promising for optoelectronic applications, specifically the TCNQ species as a candidate for new semiconducting materials in view of the clear scanning electron microscope (SEM) image observed for crystals of this product.173... 

The next question is how side-chain substitutions and skeleton conformations affect the band structures of polysilanes. Side chains provide two interesting effects (7) band gap reduction caused by substitution of larger alkyl side chains and skeleton-side chain interaction (i.e., (j-tt mixing) in aryl poly silanes. This interaction was confirmed by UV photo spectroscopy (UPS) (8-9) and photoabsorption and luminescence measurements (iO, 11). Skeleton conformations are related to thermochromism (12-17). The ab initio... 

S. M. Aldoshin, L. O. Atovmyan, and V. I. Ponomarev. Structure, spectral, luminescent and thermochromic properties of crystals of yellow modification of N-salicylidene-p-dimethyl-aminoaniline, Khim. Fiz. 3, 787-791 (1984). 

The final section Part IV is concerned with physical properties of polymeric nanocomposites (PNCs). Two types of nanoparticles, leading to two different characters and applicabilities of PNC, are discussed layered silicates (with natural or synthetic clays), used in structural-type PNCs and the others used in functional PNCs. Sender et al. in Chapter 13 describe the performance of PNCs with acicular ferroelectric particles producing PNCs with good electroactive (dc conductivity) and mechanical properties. In Chapter 15, Nicolais and Carotenuto focus on metal clusters in polymeric matrices, which combine optical transparency with magnetism, luminescence. Ultraviolet-visible absorption, thermochromism, and so on. 

The dyes 29 and 31, 32, 33 and 34 (Scheme 9) are not only vapochromic but also thermochromic and mechanochromic. Modification of the packing state by a thermal process, applied mechanical stress, and exposure to vapour is transduced to alteration of the luminescent properties of the dye according to the mechanisms discussed above. 

Thiophene (Th) and its derivatives are pol5mierized by chemical and electrochemical methods, especially poly(3-methylthiophene) (3-mTh), which was investigated because of its remarkable solid-state properties, including thermochromism, electrochromism, luminescence, and photoconductivity. Removal of two electrons (p-doping) from a polyalkylthiophene (PAT) chain produces a bipolaron structure (Fig. 3.18). 

Applications, especially those in analytical chemistry (e.g. bio-, photo- or electrochemical sensors) [17, 18] have currently been developed, as has the preparation of photochromic, thermochromic, luminescent or electrooptical materials [19-24],... 

Some materials combine different colour-changing effects, such as thermochrom-ism and fluorescence, thermochromism and piezochromism, photochromism and ther-mochromism or tribochromism and luminescence [49,89]. 

Rosenfeld, T., Ottolenghi, M., and Meyer, A.Y., Photochromic anils. Structure of photoisomers and thermal relaxation process. Mol. Photochem., 5, 39, 1973 Lambi, E., Gegiou, D., and Hadjoudis, E., Thermochromism and photochromism of N-sahcyhdenebenzylamines and N-salicylidene-2-aminomethylpyridine, /. Photochem. Photohiol, A Chem., 86, 241, 1995 Goto, T. and Tashiro, Y, Photochromism of N-salicylideneaniline single crystal, /. Luminescence., 72—74, 921, 1997. 

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