H. Nobutoki et H. Koezuka, MOLECULAR-ORBITAL STUDY ON ELECTRON CONFINEMENT CHARACTERISTICS IN HETEROAROMATIC OLIGOMERS, Journal of physical chemistry, 100(16), 1996, pp. 6451-6455
A molecular orbital study on heteroaromatic oligomers has been perform
ed to investigate their electron confinement characteristics. The semi
empirical MNDO-SCF-MO (modified neglect of diatomic overlap self-consi
stent-field molecular orbital) method was used to calculate the electr
onic structures of the oligomers as a function of the unit number for
the three sets of heteroaromatic oligomers X(n)Y(n)X(n) with unit cell
s X and Y, n = 1-4. They are X = benzene, Y = pyrrole, X = benzene, Y
= thiophene, and X = thiophene, Y = pyrrole, respectively. The electro
nic structures of the oligomers have been analyzed by means of the deg
ree of occurrence of the electron confinement divided into the sequenc
es of X units and of Y units. The analyses indicate that the oligomers
with X = thiophene, Y pyrrole can have the most promising tunable qua
ntum-well structure by controlling the unit number in the oligomers st
udied. The effect of the confinement characteristics of the oligomers
on the static second-order hyperpolarizability is also discussed.