Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 10, Issue 11, Pages 2668-2680Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200305650
Keywords
computer chemistry; electron correlation; nonlinear optics; structure-property relationships; two-photon absorption
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Quadrupolar-type substitution of pi-conjugated chromophores with donor and acceptor groups has been shown to increase their two-photon absorption (TPA) response by up to two orders of magnitude. Here, we apply highly correlated quantum-chemical calculations to evaluate the impact of the nature of conjugated bridge and the charge-transfer distance on that enhancement. We compare chromophores with phenylenevinylene-, thienylenevinylene-, polyene-, and in- denofluorene-type backbones substituted by dimethylamino and cyano groups. In all compounds, we find a strongly TPA-active A(g) state (either 2A(g) or 3A(g)) in the low-energy region, as well as a higher lying TPA-active state (mA(g)) at close to twice the energy of the lowest lying one-photon allowed state; the smaller energy detuning in the mAg states results in very large TPA cross sections delta. We also investigate the influence of the degree of ground-state polarization on TPA. Independent of the nature of the backbone and the donor-acceptor separation, 6 displays the same qualitative evolution with a maximum before the cyanine-like limit; the highest TPA cross sections are calculated for distir-ylbenzene- and polyene-based systems.
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