Luminescence solvatochromism

The use of fluorescent dyes in biological probes and sensors is covered in some detail in Chapter 3 (section 3.5.6). Because there are marked solvatochromic effects on the luminescent spectra of many fluorophores, this phenomenon is utilised to tune their performance and application in biological and other systems. 

The low temperature luminescence spectra of the title compounds in poly(methyl methacrylate) (PMMA) are shown in Fig. 4. In addition to the solvatochromic effect the MLCT luminescence bands show a pronounced rigidochromic effect. However, not only the emission energies, but also the band shapes change when the low viscosity solvents are replaced by a rigid glassy matrix. 

These bands show negative solvatochromism as revealed by band shifts to lower energy in less polar solvents [5, 7, 8, 12], The direction of the solvent dependence is associated with a reduced (and reversed) molecular dipole in their MLCT excited states. Emissions from these complexes are typically broad and structureless, and they also often exhibit a rigidochromic effect [7-12], Tables 1 and 2 summarize the luminescence characteristics and environmental effects on absorption and emission maxima for rhenium(I) tricarbonyl diimine complexes. 

The rationale for preparing this hybrid copolymer was to combine the desirable properties of polyaniline with those of polythiophene. For example, polythiophene has demonstrated thermo- and electrochromism, solvatochromism, luminescence, and photoconductivity while polyaniline has demonstrated reversible protonic dupability, excellent redox re-cyclability, and chemical stability. 

A special property of these luminescent carbonyl diimine complexes is their solvatochromic behavior. The MLCT absorption bands exhibit a noticeable red shift when the polarity of the solvents decreases (negative solvatochromism). For example, the MLCT transition of [Re(CO)3(bpy)Cl] occurred at 370 and 400 nm in CH3CN and benzene respectively. Similar solvatochromism was also observed for the charge-transfer bands of other carbonyl complexes... 

All three methods give similar values of interfacial potentials typical results for some of micelles and vesicles are listed in Table 3. Also listed are estimates of interfacial dielectric constants (e), determined by comparing the position of absorption bands of solvatochromic indicators in the surfactant assemblies with that of reference 1,4-dioxane water mixtures with known e values. More generally, luminescence probe analysis [49], thermal leasing [50] and absorption spectroscopy [47, 51] are techniques that have all been utilized to measure local polarities in micelles and vesicles. It is important to note that these methods presume knowledge of the loca-... 

The luminescent cyclometalated complex [Pt(C4ANAN)py]+ 39 immobilized in Nafion film has been observed to exhibit a solvatochromic shift in emission maximum from 530 to 650 nm upon immersion in ethanol but no effect was detected with aprotic organic solvents (Fig. 19) [41]. On the contrary, the emission of the [Pt(C4ANAN)]+ luminophore anchored on silica materials (MCM-41/-48 and silica gel) showed a blue shift from Tmax 665 to 550 nm upon exposure to pentane vapor but no shift was observed for ethanol vapor (Fig. 20). 

In the same regard, platinum(II) terpyridyl complexes (18) earn attention too. For the derivatives with X = Ph, the low-energy bands (460-600 nm) are assigned to formal LLCT states that receive substantial contribution from closely lying MLCT levels. When X = Me or Cl, luminescence of much red-shift (680-800 nm) is from MMLCT owing to metal-metal interactions occurring in head-to-tail dimers or polymers.In a recent study, large solvatochromism of the diynyl complexes (X = C C=C-C=CH), presumably due to metal-metal and -stacked interactions, has been observed. The cyclometallated phenyl bipyridine complexes (19) also show tunable excited-state properties, and the dinuclear species can reflect the metal - metal interactions in the [da ... 

In this chapter, we concentrate on luminescence approaches that are most suitable for stilbenes to be molecular probes and are based on specific and nonspecific labeling, competition, solvatochromism, experimental molecular dynamics, and singlet-singlet and triplet-triplet energy transfer. A general survey is made of the physical principles and application of the fluorescence probe methods stressing on latest developments in this area. 

Referring here only to analytical purposes, SPLS is used for detection or determination of intrinsically fluorescent or phosphorescent compounds, for non-luminescent compounds that are capable of showing luminescence when they are derivatized, for non-luminescent, nonderivatized compounds that are capable of modifying the luminescent properties of a probe, i.e., via quenching or solvatochromic effect, and for compounds that interact via a binding partner and indicate this reaction with a luminescent label. 

Yam VWW, Wong KM, Zhu N (2002) Solvent-induced aggregation through metal center dot center dot center dot metal/pi center dot center dot center dot pi interactions large solvatochromism of luminescent organoplatinum(II) terpyridyl complexes. J Am Chem Soc 124 6506-6507... 

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