Excited state molecular dynamics simulations of nonlinear push–pull chromophores

Abstract

Julolidinemalononitrile, p-nitroaniline, and julolidinyl-n-N,N 0 -diethylthiobarbituric acid are studied with ground and excited state molecular dynamics simulations in conjunction with the collective electronic oscillator formalism and OnsagerÕs cavity model. Ground and excited state geometries are calculated in the gas phase and four solvents. The results are interpreted in the context of a two-state valence bond model for charge-transfer transitions of conjugated organic molecules, and are compared to recent resonant Raman experimental results. The calculated geometries are qualitatively consistent with both the two-state model and experiment. In addition, calculated transition density matrices are presented to visualize the changes in charge distribution accompanying photoexcitation.

Role of Donor−Acceptor Strengths and Separation on the Two-Photon Absorption Response of Cytotoxic Dyes: A TD-DFT Study

“…This reflects the change of the wave function symmetry upon optical excitation to the state e. This transition can be well represented as a linear combination of neutral and zwitterionic basis resonance forms which is a typical case for push-pull chromophores. 98 Similar description is applicable to the higher lying OPA state e′ ( Figure 2). Here, wave functions of an electron and a hole have odd and even symmetries, respectively, and e′ has less zwitterionic contribution and, subsequently, less charge-transfer (CT) character compared to e. This may be the reason state e′ is not as sensitive to substitutions as state e in the OPA spectra ( Figure Figure 4.…”

Dependence of Spurious Charge-Transfer Excited States on Orbital Exchange in TDDFT: Large Molecules and Clusters

“…58,59 The zwitterionic state assumes full separation of positive and negative charges, and, consequently, it is optically forbidden. The excited state usually possesses greater zwitterionic basis state character than the ground state.…”

Enhanced Two‐Photon Absorption of Organic Chromophores: Theoretical and Experimental Assessments

“…The resulting two-level model has proved to be adequate to describe the linear and nonlinear absorption of push-pull chromophores. [127,153,221] Molecules with quadrupolar symmetry described by donor-π-acceptor-π-donor or acceptor-π-donor-π-acceptor structures, provide another simple case allowing for a reduced description. For this class of chromophores, a three-state model can be adopted, which is based on the neutral and two zwitterionic (degenerate) states.…”