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We present theoretical investigations on structure‐property correlations in fluorenone (FLO) and benzothiadiazole (BT) substituted oligofluorenes (OFLs) derived mainly from the chain morphology, thermal vibration and conjugated extent. Both the vertical absorptions and the vibrationally‐resolved absorption and fluorescence spectra have been calculated by the combination of ab initio and time‐dependent density functional theory. By properly taking into account of the anharmonic torsion potentials in the OFLs, we have reasonably reproduced the experimentally observed spectroscopic features. Both FLO and BT on‐chain chemical defects acting as charge‐trapping sites for singlet excitations, are responsible for long wave absorption and emission species, and thus alter the blue light‐emitting properties of OFLs. As temperature decreases, the electronic spectral lineshapes of FLO‐substituted oligomers become more structured. The lineshapes of BT‐substituted oligomers are always smooth and featureless because of less low collective modes resonance. A more gentle excited potential energy surface of BT‐mixed molecules can enhance electronic delocalization and achieve bigger red shifts.

The conformers of allyl alcohol and allyl mercaptan were studied with B3LYP/aug‐cc‐pVTZ method. Their relative energies were calculated at MP3, MP4(SDQ), and CCSD(T) levels. The most stable conformers for these two molecules are Gauche‐gauche′ (Gg′). The theoretical photoelectron spectra simulated with the calculated ionization energies demonstrate that there are at least four conformers in allyl alcohol and four conformers in allyl mercaptan in the gas‐phase experiments. The Dyson orbitals of the highest occupied molecular orbital (HOMO) and the next HOMO (HOMO‐1) of allyl mercaptan Gg′ conformer show strongly mixing ns and πc=c characteristics, which may be due to the resonance and inductive effects between πc=c and ns in HOMO‐1 and HOMO.

The electronic structure of five conformers of 2-chloroethanol was studied by ab initio calculations at B3LYP and MP2 levels of theory with aug-cc-pVTZ basis set. The existing hydrogen bond and hyperconjugation effects on the stability of 2-chloroethanol conformers were discussed on the base of natural bond orbital analyses. The result exhibits that hyper-conjugation is the main factor to determine the stability of conformers. Such effects on the electron wavefunctions of the highest-occupied molecular orbital (HOMO) of different conformers are demonstrated with electron momentum spectroscopy, exhibiting the obviously different symmetries of the HOMO wavefunctions in momentum space.

Fourteen conformers of 3-amino-1-propanol as the minima on the potential energy surface are examined at the MP2/6-311++G** level. Their relative energies calculated at B3LYP, MP3 and MP4 levels of theory indicated that two most stable conformers display the intramolecular OH···N hydrogen bonds. The vertical ionization energies of these conformers calculated with ab initio electron propagator theory in the P3/aug-cc-pVTZ approximation are in agreement with experimental data from photoelectron spectroscopy. Natural bond orbital analyses were used to explain the differences of IEs of the highest occupied molecular ortibal of conformers. Combined with statistical mechanics principles, conformational distributions at various temperatures are obtained and the temperature dependence of photoelectron spectra is interpreted.