Conformational Effect on the Excitonic States of 2-Phenylpyridine Oligomers: Ab Initio Studies and Analysis.

In this work, we report the effect of different conformations of 2-phenylpyridine oligomers (( PhPy ) n =1-5 ) on the excited state properties from the results obtained at the RI-ADC(2)/def2-TZVP level. Three different conformers, namely, A , B , and C , are considered for each oligomer. All the oligomers of conformer A have linear-type structures, whereas conformers B and C form helical structures at n = 5 and n = 3, respectively. The differences in the geometries of the three conformers are reflected in the UV and CD spectra. The UV spectra of conformer A show high-intensity peaks compared to the conformers B and C , for each oligomer. While the helical oligomers of conformers B and C show high-intensity CD bands, the intensities of CD bands for all of the oligomers of conformer A are weaker. Analysis of the properties of the first five excited states in ( PhPy ) 5 is carried out using three descriptors, and the results reveal that these are partially charge transfer states.