Conformations and rotational barriers of 2,2?-bithiazole and 4,4?-dimethyl-2,2?-bithiazole semiemperical, ab initio, and density functional theory calculations

Accurate Prediction of Band Gaps in Neutral Heterocyclic Conjugated Polymers

“…In the present work, molecules having extended conjugation show small errors in the computed excitation energies with HF/RPA even before empirical correction via linear regression, as seen in Figures d and d. For AM1-predicted geometries, the method even gives slight under-predictions for molecules 26 and 28 , although these molecules would be expected to have significant inter- ring dihedral angles which may not be treated well by the AM1 method. − For example, the predicted geometry of molecule 26 shows average dihedral angles of 39.1° and 45.2° for AM1 and DFT optimizations, respectively, and the geometry of molecule 28 shows average dihedral angles of 39.6° and 43.9° for AM1- and DFT-optimized geometries, respectively. On the other hand, the maximum absolute error in computed excitation energy for AM1 geometries (as for HF/CIS) is found for molecule 20 , which is also obviously expected to exhibit large dihedral angles.…”

Hopping Transport in Conductive Heterocyclic Oligomers: Reorganization Energies and Substituent Effects

“…The internal harmonic reorganization energies were then calculated from these relaxed geometries, as given by eq 3, and summarized in Table , as were the adiabatic ionization potentials of each species, given by the following: Torsional profiles were computed for each dimer by increasing the inter-ring dihedral angle in 15° increments. Previous studies have demonstrated that electron correlation is important in computing λ, and DFT methods generally give both reorganization energies comparable to those from second-order Møller−Plesset (MP2) calculations, (slightly lower than that measured experimentally from photoelectron spectroscopy for fused-ring aromatic molecules), and reasonable estimates of the inter-ring torsional barriers in conjugated organic oligomers 1 Computed Internal Reorganization Energies (λ, in eV) for Hole Transfer (eq 3) for Each of the Oligoheterocycles of Figure seriesmonomer unitsλseriesmonomer unitsλseriesmonomer unitsλ 1 2 0.365 8 2 0.353 15 2 0.315 3 0.321 3 0.312 3 0.292 4 0.293 4 0.281 4 0.271 5 0.272 5 0.253 5 0.252 6 0.253 6 0.228 6 0.234 2 2 0.210 9 2 0.295 16 2 0.195 3 0.202 3 0.330 3 0.189 4 0.522 4 0.287 4 0.191 5 0.428 5 0.265 5 0.190 6 0.510 6 0.334 6 0.183 3 2 0.409 10 2 0.413 17 2 0.388 …”

Investigation of triptycene-based surface-mounted rotors

“…The internal rotational barrier of molecules has been investigated using the AM1 method. The AM1 values are often quite good compared with experimental values or other more accurate but more computationally expensive methods such as the density functional theory approach 4 (DFT) [15][16][17][18], though the AM1 values are sometimes smaller, since the electron correlation effects are implicitly taken into account 4 We compared the rotational barrier of a biphenyl molecule calculated by AM1 and B3LYP/6-31G(d). The difference in total energy between a forced planar state and an optimized twisted structure was defined as the rotational barrier; the experimental value was 1.4 ± 0.5 kcal mol −1 .…”