Steady-state optical properties

Measuring the steady state optical absorption and emission properties of any luminescent polymer is the most basic but fundamental photophysical measurement we can make. Figure 1 depicts both the absorption and emission spectra for a series of polyfluorene oligomers and poly[9,9-di- -(2-ethylhexyljfluorene] (PF2/6), along with the fully rigid ladder type MeLPPP. 

A review of rheo-optical techniques by Sherman et al. (1996) notes that there has been an increase in the use of rheo-optic set-ups both for FT-IR dichroism and for dynamic IR dichroism spectroscopies for polymer melts and polymer blends. Skytt et al. (1996) highlight the use of simultaneous measurement of the transient or steady-state rheological properties and IR dichroism to characterize orientation in polymer melts. However, there is little reference to dual spectroscopic-rheological techniques for reactive polymer systems in the literature. 

Molecular rotors are useful as reporters of their microenvironment, because their fluorescence emission allows to probe TICT formation and solvent interaction. Measurements are possible through steady-state spectroscopy and time-resolved spectroscopy. Three primary effects were identified in Sect. 2, namely, the solvent-dependent reorientation rate, the solvent-dependent quantum yield (which directly links to the reorientation rate), and the solvatochromic shift. Most commonly, molecular rotors exhibit a change in quantum yield as a consequence of nonradia-tive relaxation. Therefore, the fluorophore s quantum yield needs to be determined as accurately as possible. In steady-state spectroscopy, emission intensity can be calibrated with quantum yield standards. Alternatively, relative changes in emission intensity can be used, because the ratio of two intensities is identical to the ratio of the corresponding quantum yields if the fluid optical properties remain constant. For molecular rotors with nonradiative relaxation, the calibrated measurement of the quantum yield allows to approximately compute the rotational relaxation rate kor from the measured quantum yield [Pg.284]

Farrell TJ, Patterson MS, Wilson B. A diffusion-theory model of spatially resolved, steady-state diffuse reflectance for the noninvasive determination of tissue optical properties in vivo. Medical Physics 1992, 19, 879-888. 

Doornbos RMP, Lang R, Aalders MC, Cross FW, Sterenborg HJCM. The determination of in vivo human tissue optical properties and absolute chromophore concentrations using spatially resolved steady-state diffuse reflectance spectroscopy. Physics in Medicine and Biology 1999, 44, 967-981. 

Nichols MG, Hull EL, Foster TH. Design and testing of a white-light, steady-state diffuse reflectance spectrometer for determination of optical properties of highly scattering systems. Applied Optics 1997, 36, 93-104. 

As described in the previous section, we incorporated Et as an artificial DNA base at specific sites in duplex DNA (Fig. 12.12) [44-46]. Temperature-dependent absorption and steady-state fluorescence measurements prove the intercalation of the Et moiety in duplex DNA [44], The intercalation properties of the Et moiety do not depend significantly on the local duplex environment. Interestingly, the optical properties of Et seem not to interfere with the presence of the different counterbases T, G, C or A [45]. This result is remarkable with respect to the steric demand of the Et heterocycle and indicates a bulged position of the counterbase. 

A large number of electrochemical methods exist which are or have the potential to be useful in the study of reactive intermediates. The methods are conveniently categorized according to the quantity measured, usually the current, potential, or some optical property of the reactants or the intermediates. A further classification arises from the manner in which experiments are conducted, i.e. transient or steady state measurements. In this brief survey only those techniques which have been reduced to useful practice are discussed and even then the coverage is not exhaustive. More detailed discussion can be found in several excellent references sources (Bard, 1966-present MacDonald, 1977 Bard and Faulkner, 1980). 

Kramers (44) in 1944 published an elegant paper on the mechanical and optical properties of dilute suspension of bead-rod systems in steady-state, homogeneous, potential flow [see comments just after Eq. (3.1)]. This theory has recently been extended by Bird, Johnson, and Curtiss (5) to include bead-spring systems as well. The latter theory gives for a system of N beads with any kind of connectors ... 

Fig. la demonstrates the evolution of optical properties of CdTe NCs as their size increased from 1.8 to 4.4 nm. The well-pronounced absorption peaks are indicative of a narrow size distribution of CdTe NCs, which was estimated to be about 10-12%. The steady-state PL (SSPL) spectrum excited by the Xe-lamp (2ex = 400 nm) consists of one sharp peak of band-edge emission. 

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