Triplet optical processes

Unlike TBHF and TIHF, the dyes containing the CN-group at C-9 position give triplets which decay by first-order kinetics not influenced by dye concentrations or laser dose. Thus we observed no triplet-triplet annihilation process. This observation may be due to insufficiency of the absorbed energy (optical densities for the CN-containing dyes are much less at Aex than for H-dyes at the same concentration), but we had to carry out our experiments using low dye concentrations in order to avoid the aggregation processes which are well known for xanthene dyes. 

Laser flash photolysis techniques offer the possibility of examining in detail the transient processes responsible for the photostabilizing effect discussed above. The triplet lifetimes are frequently too short, even for this technique however, they can still be estimated using as a probe the quenching by 1-methyl-naphthalene, which leads to the formation of its easily detectable triplet. The optical absorbance due to the 1-methylnaphthalene triplet (Aft) produced as a result of energy transfer is related to the Stern-Volmer slope by equation 5, where N stands for... 

In addition to heat emission, radiative decay processes may also occur, in which light is emitted due to a transition from the lowest excited singlet or triplet state to the ground state (fluorescence or phosphorescence). In order to effect rapid and efficient conversion of optical energy (the laser) to heat, dyes which exhibit low fluorescence and in which excitation primarily involves the singlet states are the most suitable for heat-mode recording.196... 

As resonant processes are avoided in the nonlinear optical experiments (except where two-photon absorption is optimized), no excited state molecules are created and triplet states are of no concern. For a more thorough investigation of the absorption process also the vibrations of the molecule have to be included. They are not considered here. 

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