Photophysical hole burning

An interesting ansatz for this problem is based on photochemical or photophysical hole-burning. The principle is explained in Fig. 12.16. The emission as well as the absorption spectra of molecules in a solid matrix, or also in an organic glass, consists in general of relatively broad bands. They are inhomogeneously broadened, since the molecules, which have intrinsically sharp absorption and emission lines, experience a multiplicity of different local environments in the matrix, with different values of the so-called solvent shift. The observed spectrum is then a superposition of many individual sharp lines, and one observes only their broad envelope. 

Hole burning The photohleaching of a feature, normally a narrow range, within an inhomogeneous broader absorption or emission band. The holes are produced by the disappearance of resonantly excited molecules as a result of photophysical or photochemical processes. The resulting spectroscopic technique is site-selection spectroscopy. 

It is not surprising that the triplet states of porphyrins attract interest. A comprehensive study of some purpurins with Sn(lV) substitution involving observations of absorption, fluorescence and triplet spectra and 2 formation and the triplet state of sapphyrin dication (a large porphyrin like system) shows an unusual spin alignment in the monomer and spin delocalization in dimers " are systems of photophysical interest. The influence of external parameters on time resolved transient hole burning in porphyrins shows the effects of a triplet state bottleneck in the rate of state build up". ... 

Saturation of an optical transition ( hole-burning ) and subsequent analysis of the time and frequency-dependence of the recovery of the ground-state species has become a well-known technique for the study of the picosecond photophysics of radiationless transitions in stable molecules, transient species, and laser dyes in particular. " ... 

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