Transition dipole dimer

C3.4.13)). The dimer has a common ground state and excitation may temrinate in eitlier tire or excited state (see tire solid arrows in figure C3.4.3). The transition dipole moments of tliese transitions are defined as ... 

Figure C3.4.4. Definition of the dimer transition dipole moments and p on tire basis of tire monomer transition dipole moments p and P2-...

For large interchain separations (8 A < R < 30 A), the LCAO coefficients of a given molecular orbital are localized on a single chain, as intuitively expected. The lowest excited state of these dimers results from a destructive interaction of the two intrachain transition dipole moments, whereas a constructive interaction prevails for the second excited stale. This result is fully consistent with the molcc-... 

Figure 6.5. Exciton model for the coupling of dimers. When the transition dipoles are aligned (ft, W) in a card pack fashion only the transition to n is allowed thus a blue shift in the spectrum is expected.

The Anisotropy Between the Transition Dipole Moments of the Chromophores in the Dimer Model... 

Figure 1.3 Molecular structure of Sulforhodamine B and exciton band energy diagram for molecular dimers with oblique and coplanar inclined transition dipoles. (Reproduced from ref. 10, with permission.)...

Figure 4 Exciton band structures in dimers with several orientations of transition dipoles. Dotted arrows indicate dipole forbidden transitions. (Adapted from Kasha [17]).

The excimer fluorescence (with respect to the excited vdW dimer emission) is red shifted and structureless because the emission is terminated in a repulsive ground-state potential energy surface (Figure 15). For parallel transition moments, emission from the out-of-phase exciton state to the ground state is forbidden and for the in-phase exciton state emission is allowed [28a]. It should be noted, however, that the forbidden emission from the out-of-phase exciton state is expected to have a similar transition dipole moment as the Lb So emission. The actual dynamics of the initially excited vdW dimer depend on the energy gap and the coupling strength between the primary excited (LE) state and the excimer state. 

Figure 47. Idealized energy levels and most probable electronic absorptions, ffabs, of one monomeric and two dimeric dye structures. The arrows represent the directions of the localized transition dipole moments. The transition in the face-to-face aggregate is representative of that in an H-aggregate and the transition in the end-to-end structure is representative of that in a J-aggregate.

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