Predicting Excitation Energies of Twisted Intramolecular Charge-Transfer States with the Time-Dependent Density Functional Theory: Comparison with Experimental Measurements in the Gas Phase and Solvents Ranging from Hexanes to Acetonitrile.

摘要: Electronically excited states characterized by intramolecular charge transfer play an essential role in many biological processes and optical devices. The ability to make quantitative ab initio predictions of the relative energetics involved is a challenging yet desirable goal, especially for large molecules solution. In this work, we present data set 61 experimental measurements absorption emission processes, both gas phase solvents representing broad range polarities, which involve mediated nonzero, "twisted" dihedral angle between one or more donor acceptor subunits. Among variety density functionals investigated within framework linear-response theory, "optimally tuned" LRC-ωPBE functional, utilizes system-specific nonempirical procedure specify range-separation parameter, emerges as preferred choice. For entire excitation energies, involving changes dipole moment ranging from 4 >20 Debye, mean signed absolute errors are 0.02 0.18 eV, respectively (compared, e.g., -0.30 0.30 PBE0, 0.44 0.47 LRC-ωPBEh, 0.83 ωB97X-V). We analyze performance polarizable continuum solvation models available Q-Chem that partition solvent response into fast slow time scales, clear trends emerge when corresponding four small 4-(dimethylamino)benzonitrile (DMABN)-like charged species excluded. case found only weak cannot be expected improve via optimal tuning procedure, enforces condition exact well-separated donor-acceptor limit, empirical evidence implicating outsized importance systems relaxation effects accounted time-dependent functional theory adiabatic approximation. Finally, demonstrate utility optimally tuned approach targeting charge-transfer biomimetic model system light-harvesting structures Photosystem II.