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Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies
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10.1063/1.2829531
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Affiliations:
1 Institut für Physikalische Chemie, Universität Mainz, D-55099 Mainz, Germany
a) Electronic mail: andreas.koehn@uni-mainz.de.
J. Chem. Phys. 128, 074505 (2008)
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## Figures

FIG. 1.

The dyads studied in Refs. 31–33 consist of the chromophores PDI and TDI linked via an oligophenylene bridge. For our quantum chemical calculations with the isolated chromophores we saturated the nitrogen sites with hydrogen atoms, whereas the experimental data for the single chromophores originate from measurements on Ph-PDI-Ph and Ph-TDI-Ph.

FIG. 2.

The results of B3LYP/SVP calculations for (a) the electronic coupling strength vs the donor-acceptor distance . The dashed lines denote the dipole-dipole approximated coupling strength and the straight line marks the full Coulomb coupling strength . (b) Ratio of the two calculated coupling strengths. Throughout the figure the (◻) denote the collinear alignment of the interacting chromophores, the (○) the coplanar case, and the (+) the cofacial alignment. The arrow indicates the geometry of dyad 1 (collinear, ).

FIG. 3.

The results of B3LYP/SVP calculations for (a) the electronic coupling strength vs the donor-acceptor distance . The dashed lines denote the dipole-dipole approximated coupling and the straight line marks the full Coulomb coupling . (b) Ratio of the two calculated coupling strengths. Throughout the figure the (◻) denote , the (×) , the (▿) , the (▵) , the (◇) , and the (+) . For reasons of clarity not all alignments are displayed in panel (a).

FIG. 4.

The results of B3LYP/SVP calculations for the electronic coupling of PDI and TDI with respect to the average geometry of dyad 2 (, , ). (a) The electronic coupling strength vs the donor-acceptor distance . The dashed line denotes the dipole-dipole approximated coupling and the straight line marks the full Coulomb coupling . (b) Ratio of the two calculated coupling strengths.

FIG. 5.

Influence of the -terphenyl bridge on the first excited singlet state of PDI: Shown are the isosurfaces of the (a) transition density and (b) difference density of PDI-3Ph as calculated with CC2/SVP.

## Tables

Table I.

The calculated electronic transitions of PDI in the gas phase. The values of the transition energies and the transition dipole moment magnitudes are listed. The absorption and emission transitions were calculated from the optimized ground and first excited state geometries, respectively. For comparison the absorption and emission maxima obtained by experiment and the absorption transition dipole moment magnitude extracted from the absorption spectrum of Ph-PDI-Ph in a toluene solution are given.

Table II.

The calculated absorption transitions of TDI in the gas phase. The values of the transition energies and the transition dipole moments are listed. For reasons of comparison the maximum and the transition dipole moment of the experimentally obtained spectrum of Ph-TDI-Ph in a toluene solution are given.

Table III.

Electronic couplings as obtained by quantum chemical calculations (CC2/SVP) considering separated chromophores (no bridge effects) for the dyads 1 and 2. The superscripts “full” and “” denote whether the respective electronic coupling was obtained using the full interaction operator [cf. Eq. (8)], or in the dipole-dipole approximation [cf. Eq. (9)].

Table IV.

The first five calculated absorption transitions of -terphenyl in the gas phase. The values of the transition energies and the transition dipole moments are listed.

Table V.

Effect of the bridge on the electronic coupling of PDI and TDI, as calculated at the CC2/SVP level. is the direct coupling term given in Table III, is the additional contribution from the bridge. The superscripts “full” and “” denote the considered electronic coupling, i.e., the full [cf. Eq. (8)] and the dipole-dipole approximated [cf. Eq. (9)] coupling. The contribution of the bridge (index “D-B-A”) has been considered in different ways: For compound 1 (, ) we calculated the additional coupling resulting from the first-order perturbation approach of Eq. (11) and we furthermore considered the coupling between PDI-3Ph (cf. Fig. 5) and TDI, Eq. (13). For compound 2 (, ) we calculated the coupling between PDI-2Ph and 3Ph-TDI.

Table VI.

The EET rates from both, experiments (Refs. 31–33) and quantum chemical calculations (CC2/SVP, this work) for the dyads 1 (, ) and 2 (, ). The superscripts “exp” and “Förster” denote the rates that have been directly measured and approximated with Eq. (1), respectively. The values given denote the rate average and the inverse time average determined from distributions as explained in Sec. II. The superscripts “full” and “” denote the approximations used for calculating the respective electronic couplings, i.e., the full [cf. Eq. (8)] and the dipole-dipole approximated [cf. Eq. (9)] coupling. To obtain the rates from the computed couplings the mean line shape overlaps of the experimental spectra were used [cf. Eq. (10)]. The value for dyad 1 is [from single molecule spectra at in PMMA [Refs. 32], for dyad 2 a value of [from single molecule spectra at room temperature in PMMA [Ref. 33] was used. The shielding factor was set to (with ) as in Refs. 31–33.

/content/aip/journal/jcp/128/7/10.1063/1.2829531
2008-02-21
2014-04-20

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