%0 Journal Article
%T A Quantum Chemical Study on Structures and Electronic (Hyper)polarizabilities of 2,2¡ä-Biselenophene Rotamers
%A Andrea Alparone
%J ISRN Physical Chemistry
%D 2013
%R 10.1155/2013/251635
%X Geometries, IR and Raman spectra, nucleus independent chemical shifts, and static electronic (hyper)polarizabilities of the equilibrium conformations of 2,2¡ä-biselenophene were determined in vacuum using density functional theory (DFT) computations. At the DFT-PBE0/6-31G+pdd¡ä level the antigauche structure characterized by the dihedral angle of 157¡ã is the global minimum, whereas the syngauche rotamer ( = 40¡ã) lies ca. 0.7£¿kcal¡¤mol£¿1 above the antigauche form. The structural and spectroscopic properties as well as the electronic polarizability of the antigauche are similar to those of the syngauche structure. On the other hand, the dipole moments and first-order hyperpolarizabilities are strongly influenced by the conformational characteristics, increasing by ca. a factor of five when passing from the antigauche to the syngauche form. 1. Introduction Oligomers and polymers based on five-membered heterocycles have received great attention as promising conductive and nonlinear optical (NLO) materials [1¨C3]. Although the major efforts have been principally directed towards polyfurans, polypyrroles, and especially polythiophenes, recent studies have been also dedicated to the properties of polyselenophenes [4, 5]. Selenophene, owing to the intrinsic effects of the heavy atom, is considered an interesting building-block for the design of NLO devices [6¨C10]. Physicochemical properties of -conjugated oligomers and polymers are usually influenced by the twisting degree of the backbone as well as by the extension of the electron delocalization [11, 12]. However, structural and electronic properties of large oligomers and polymers can be extrapolated by using data of smaller oligomers [11, 12]. Differently from the monomer, little is known about the physicochemical properties of the smallest oligoselenophenes. Structures and torsional potentials of 2,2¡ä-biselenophene, 2,2¡ä:5¡ä,2¡ä¡ä-terselenophene, and 2,2¡ä:5¡ä,2¡ä¡ä:5¡ä¡ä,2¡ä¡ä¡ä-quaterselenophene have been previously investigated by using ab initio and density functional theory (DFT) methods [13, 14]. On the basis of the most recent theoretical results obtained in vacuum, 2,2¡ä-biselenophene is predicted to exist in two nonplanar minimum-energy conformations, characterized by dihedral angles of ca. 150¡ã (antigauche) and 40¡ã (syngauche) [14]. The antigauche is the lowest-energy conformer, with the syngauche being predicted to lie above the antigauche structure by less than 1£¿kcal/mol [13, 14]. The torsional potentials of 2,2¡ä-biselenophene for the 0¡ã¨C360¡ã rotation around the bond are described by flat four-well potentials,
%U http://www.hindawi.com/journals/isrn.physical.chemistry/2013/251635/