Three-level TPA model

Figure 3.29. Theoretical three-level model for description of TPA in monomeric (n — 1) and dimeric (n — 2) forms. (From Ref. [296] with permission of Elsevier.)...

Fig. 2 Schematic representation of the TPA process, (a) In the case of the three-level model for symmetric systems (b) in the case of the two-level model for noncentrosym-metric systems...

Using these exponents in the three-level model, one finds a cttpa power dependency a = 3.5 in good agreement with the power a = 3.0 obtained from the CNDO/S calculation. Thus, on the basis of the three-level model, the enhancement of polyphenyl TPA can be rationalized by the simultaneous increase of groimd-state transition dipole moment fioi, excited-state transition dipole moment fiu, and energy resonances with the number n of monomer units. The power dependency of transition dipole moments, i.e. a = 0.67 and... 

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