INDO/SCI

Excited-state wavefunction analyses arc carried out in the framework of the Intermediate Neglect of Differential Overlap/Single Configuration Interaction (INDO/ SCI) technique to characterize the properties of the photogenerated electron-hole pairs. The SCI wavefunction writes ... 

Figure 4-6. Evolution of the INDO/SCI-calculalcd. splitting between the lowest two oplieal transitions of cofacial dimers formed by two PPV chains as a function of the inverse number of bonds (1/u) along the conjugated backbone of the oligomer. The theoretical results are reported for interchain distances of 4 A (open circles) and C> A (tilled circles).

Figure 4-2. INDO/SCI-siuiulaled linear absorption spectrum of the eleven-ring PPV oligomer. The vertical lines represent the oscillator strength of the transitions that are described the site labeling used tor the wavcluiiclion analyses is shown on lop.

Figure 4-3. Absolute values of the INDO/SCI-calculalcd electron wavcfunctions v/(a, jt, = 34) calculated for the eleven-ring PPV oligomer as a function of carbon site (hole fixed on site 34) for the excited stales corresponding to (a) die first absorption peak (3.0 cV) (b) the second absorption peak (3.8 eV) (c) the third absorption peak (5.6 eV) (d) lire fourth absorption peak (6.3 eV) and (e) lire fifth absorption peak (7.0 cV). The energies given between parentheses refer to the theoretical values.

Table 4-1. INDO/SCI-calculalcd iransilion energies, intensities, and Cl dcscriplions of llie lowest two excited stales (S and S2, respectively) of a cofacial dimer formed by Iwo stilbene molecules for various interchain distances.

Figure 4-9. INDO/SCI-simulalcd absorption and emission spectra of two slilbene molecules with a huge interchain distance (solid lines) and those of a cofacial dimer formed by two slilbene chains separated by 4 A (dolled lines).

We note dial highly correlated calculations performed on isolated slilbene indicate that the first excited stale strongly optically coupled lo die ground stale is mil (he lowest in energy, in contrast to the INDO/SCI results [44 however, emission lakes place from the strongly coupled excited stale when relaxation effects are considered thus, the exact ordering of the lowest two excited stales in slilbene does not modify the main conclusions of our study. 

Fig. 6.1 Experimental (lower part) and INDO/SCI-calculated (upper part) absorption spectra of the two- (solid line), three- (dashed line), four- (dotted line) and five-ring (dash-dotted line) PPV oligomers.

Firstly, we focus on cofacial dimers formed by stilbene molecules in such conformations, the amplitude of interchain interactions is expected to be maximized [57]. Table 4-1 collects the INDO/SCI-calculated transition energies and intensities of the lowest two excited states of stilbene dimers for an interchain distance ranging from 30 to 3.5 A. 

Figure 4-5. INDO/SCI-calculated transition energies of the lowest two optical transitions of a cofacial dimer formed by two stilbene molecules as a function of interchain distance. The horizontal line refers to the transition energy of the isolated molecule. Note that the upper value reported at 3.5 A corresponds to the transition to the fifth excited state, which provides the lowest intense absorption feature.

F re 4-7. INDO/SCI simulation of the first singlet excited state wavefunction in a cofacial dimer formed by two five-ring PPV oUgomers, = 16, chain 1), assuming an intermolecular dis-... 

Figure 4-8. INDO/SCI simulation of the wavefunction i// xe,Xk = 16, chain I) of the lowest charge transfer-excited state in a cofacial dimer formed by two five-ring PPV oligomers separated by 4 A. t// xe,xi, = 16, chain 1) represents the probabdity amplitude in finding an electron on a given site Xe assuming the hole is centered on site 16 of chain 1. The site labeling is the same as that reported on top of Figure 4-7.

Fig. 4-14. INDO/SCI-simulated absorption spectra of a cluster containing six molecules on top of each other within the same layer, for polarizations along the b (dotted line) and c (solid line) axes.

Fig. 8. Molecular structure of two interacting molecules forming a cross-like dimer (left) and (right) Intermediate neglect of differential overlap/ single configuration interaction (INDO/SCI) excitation-energy shifts due to intermolecular interactions. The scale on the right corresponds to calculated excitation energy shifts.

Table 5. INDO/SCI-SOS Calculated /i Values at 1064nm for Porphyrin-Bridged Donor-Acceptor Molecules...

It is usual in quantum chemistry to use different methods for geometry optimization and for the subsequent determination of the molecular properties. In addition to the different geometries used as input, we have therefore also applied different methods for the calculation of the optical transitions to the electronic excited states, namely, INDO-SCI and time-dependent DFT (TD-DFT). Interestingly, a Mulliken population analysis for the 7-ring OPV radical-cation, presented in Figure 1.10, demonstrates... 

Table 52, reproduced from Kotzian et al. s work, compares the INDO/SCI energy separations with experiment for several electronic states of LaO. It is evident from table 52 that the INDO/S-CI method predicts the energy separations for these compounds reasonably well. Kotzian et al. also computed the transition moments for the observed A<->C, B<- X, C<- X, D<- X and F<- X systems. 

So far we are still using Zerner s INDO/SCI parametrization except for setting f7=l. This seems appropriate as the amount of explicit electron correlation still is small. 

Fig. 1.2 INDO/SCI simulated optical absorption spectrum of the five-ring PPV oligomer. Shown in the insert is the experimental spectrum of the polymer (From Ref. 49.)...

Table 2. Energy (in eV) of the HOMO and LUMO levels, lowest transition energy (Eu, in eV) and related oscillator strength (OS, in arbitrary units) of the coplanar cyano-substituted oligothiophenes in a planar conformation, as provided by INDO/SCI calculations. We present in parentheses the INDO shifts of the frontier levels (with respect to a reference compound in each group) that are compared to the corresponding experimental values appearing in bold [80].

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