Temperature steady-state emission spectra

A map of the singlet-singlet excitation and photoisomerization potential energy surface for tetraphenylethylene in alkane solvents were prepared using fluorescence and picosecond optical calorimetry (Figure 3.4) [4]. The line shapes of the vertical and relaxed exdted-state emissions at 294 K in methylcyclohexane were obtained from the steady-state emission spectrum, the wavelength dependence of the time-resolved fluorescence decays, and the temperature dependence of the vertical and relaxed state emission quantum yields and of the time-resolved fluorescence decays. 

In good solvents at ambient temperature, the excited state (67 ) will quickly relax to the planar form, so that only the 0-0 emission from Si is detected in steady-state emission. If the same experiment is performed at low temperature and in a viscous solvent, the molecular torsion of 67 in attaining its planar form is hampered by the medium, and planarization is slow on the timescale of the fluorescence lifetime (355 ps). Emission will not only occur from the potential minimum of the lowest excited state, but from virtually all frozen ro-tamers resulting in a broad and blue-shifted spectrum. Only after planarization of 67 is complete narrow emission from the lowest excited-state conformation will reoccur. Consequently, planarization of the excited state rather than energy migration is likely to govern the emission behavior in PPEs such as 12. 

Luminescence of Ti was not confidently detected in steady-state luminescence spectra of minerals. In Ti minerals studied by laser-induced time resolved spectroscopy broad read band have been found with decay time of several ps at 660 nm in benitoite (Fig. 4.82) and 750 nm in titanite (Fig. 4.801). At room temperature the benitoite band with a maximum at 660 nm has half-width of 135 nm and may be approximated by one Gaussian (Gaft et al. 2004). One exponent with decay time of 1.1 ps approximates well its decay curve at room temperature in all spectral range of luminescence band. At lower temperatures up to 30 K this red luminescence intensity becomes approximately ten times higher and the spectrum undergoes certain changes, namely its maximum shifts in long wave direction to 668 mn and the band becomes a little narrower with half-width of 105 mn. Such red emission is not excited by laser sources in the visible part of the spectrum, such as 488, 514 and 532 mn. Excitation spectrum at lower temperatures, when... 

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