Time-resolved emission spectra TRES

The time-resolved emission spectra (TRES) and fluorescence lifetimes, ti, of the fluorene derivatives were measured in liquid solutions at room temperature with a PTI QuantaMaster spectrofluorimeter with 0.1 ns temporal resolution [20]. At this resolution, all investigated fluorenes exhibited TRES which were coincident with the corresponding steady-state fluorescence spectra. As an example, TRES for compounds 3 and 11 in hexane, THE, and ACN are presented in Eig. 8 for different nanosecond delays 0 ns (curves 2,4,6) and 5 ns, which modeled the steady-state condition (curves 3,5,7). No differences in the fluorescence spectra for these two delays were observed, indicating that all relaxation processes in the first excited state Si are sufficiently fast for fluorene molecifles and did not exceed the time resolution of the PTI system ( 0.1 ns). 

The appearance of the new, red, long-lived exciplex emission becomes even more obvious when plotting three-dimensional, time-resolved emission spectra (TRES). Figure 2.12 shows that the PL emission of the pure polymers decays monoexponentially with no spectral changes throughout their lifetime, whereas the blend PL evolves into the red exciplex peak. 

Time-resolved emission spectra Although there have been several attempts to simplify the characterisation of the SR process, the determination of time-resolved emission spectra (TRES) is certainly the most general and most precise way to quantitatively describe the solvent response. The time-resolved emission spectra are usually determined by spectral reconstruction [96, 97, 106]. The time-resolved emission spectrum at a given time t is calculated from the wavelength dependent time-resolved decays by relative normalization to the steady-state spectrum [107]. By fitting the TRES at different times t by the empirical log-normal function, the emission maximum frequencies i (t) (or 2(t) see Fig. 6.26) and the total Stokes-shift Ac (or A2) are usually derived [106]. Since c(t) contains both information about the polarity (Ac) and the viscosity of the reported environment, the spectral shift c(t) may be normalized to the total shift Ac. The resulting correlation functions C(t) (Eq. (7)) describe the time course of the solvent response and allow for comparison of the SR-kinetic and, thus, of relative micro-viscosities, reported from environments of different polarities [96, 97, 106, 108, 109, 116, 117, 122]... 

The time-resolved emission spectra (TRES), ErR(v,f), were reconstructed using the steady-state emission spectrum, F(v), and the fluorescence decays, /(v,f), measured at different wave numbers v, according to the formula [130] ... 

Tune-dependent special shifts are usually studied by measurement of the time-resolved emission spectra (TRES). The TRES are die onissicMi spectra wtudi would be obs ed if measured at some instant in time following pulsed excitation. Suppose diat die r e of solvent or spectral relaxation (ks) is compar le to the intensity decay rate (1/t). as shown in Figure 7.1. In this situation, the solvent relaxation time xs - ) is comparable to the lifetime (t). 

Apomyogldun, 255. 304.364-365 amsotiopy decay, 334-336 time-resolved emission spectra (TRES), 215-217... 

The time-resolved emission spectra (TRES) were constructed using a method described elsewhere [116,117]. Briefly, both the red- and bine-edge decay profiles were best fitted to multiexponents. The TRES at time f, S(A t), is obtained from the... 

The time-resolved emission spectrum (TRES) is usually not measured directly. Instead, it is obtained by the so-called spectral reconstruction method from a series of emission decays D(co,t) measured by various wave numbers co. TRES is then... 

In Fig. 13 are shown the rectra, measured from separate solutions of MOI and AMP in water. The lifetimes of MOI and AMP, measured by fitting decay curves from the separate solutions to single exponential functions, were 4.48 ns and 9.57 ns respectively. Therefore the ectrum obtained from a mixture of MOI and AMP in water presented in Fig. 14 ould be resolvable into die two spectra of Fig. 13 using Method I. The TRES depicted in Fig. IS illustrate this separation. It will be seen that the EGS diows a broadening to the red compared to the MOI spectrum while the LGS is broader to the blue than the AMP qiectrum. This is expected in view of the fact that AMP makes some contribution to the emission even at extreme diort times while at a At of 54 ns there is still some fluorescence from MOI. These ectra clearly demonstrate that TRES collected in this way are a good diagnostic tod in examining complex spectra but will not completely separate the individual components when the lifetimes of each species are not very different. 

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