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ABSTRACT:In this article, we present quantum chemical calculations, based on density functional theory (DFT), performed to investigate the geometries and the opto-electronic properties of a new synthesized graft copolymer based on poly(N-vinylcarbazole) (PVK) and poly(3-methylthiophene) (PMeT) named PVK-3MeT. First, we have theoretically computed and compared the structural, optical, and vibrational parameters of both neutral and doped states. In addition, the excited state was theoretically obtained by the ab initio RCIS/ STO-3G method. To assign the absorption and emission peaks observed experimentally, we computed the energies of the lowest singlet excited state with the time-dependent density functional theory (TD-DFT) method. Electronic parameters such as the HOMO-LUMO band gap, the ionization potential (IP), and electron affinity (EA) are extracted. Calculations show that the PVK-3MeT copolymer is nonplanar in its ground neutral state. Meanwhile, upon doping or photoexcitation, an enhancement of the planarity is observed, resulting on a decrease of the inter-ring torsion angle between 3-methylthiophene units. Such modifications in the geometric parameters induce a dramatic change on the HOMO and LUMO orbitals in the doped or excited states.

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International audienceSteady-state and time-resolved photoluminescence (TRPL) measurements are used in order to investigate the emission properties of new graft copolymer involving poly(N-vinylcarbazole) (PVK) and poly(3-methylthiophene) (PMeT) named PVK-3MeT. The photo-generated species in PVK-3MeT are identified as singlet intrachain excitons. Furthermore, radiative and nonradiative lifetimes have been calculated. The observed changes in the photo-physical properties of the different condensed phases could be directly related to the nanostructure of the material. The use of PVK in the chemical synthesis allows the obtaining of a new organic material with better emission and slowly radiative recombination compared to those of polythiophenes indicating that the radiative channel is more enhanced

In this paper, geometrical (in ground and excited states), electronic, optical and charge transfer properties, (ionization potentials (IP), electron affinities (EA) and HOMO-LUMO gaps (∆E H-L ), as well as the lowest excitation energies (E ex ) and reorganization energies) of the phenylene-tiophene oligomers are studied by the density functional theory (DFT) and Time-dependent DFT approaches. Based on the density functional theory (DFT/B3LYP and CAM -B3LYP functional with 6-31G (d,p) basis set), we will highlight the effect of terminal acceptor/donor (CN, NO 2 , and CF 3 ) /OCH 3 , N(CH 3 ) 2 substituents on thiophene-phenylene derivatives. The excited state indicates more planar structures of the co-oligomers, which leads to a decrease in the (HOMO-LUMO) gap compared with the ground state, especially when the acceptor character increases. Furthermore, the vinyl spacer and cyanide ((-CN) functional group (Compound C 8 ) stabilize the LUMO levels of energy and improve the transport properties of the thiophene-phenylene derivatives. Comparing with the donor groups, the results show that the electron withdrawing substituents are remarkable on the energy levels of the frontier molecular orbitals, and on the transport charge proprieties in these co-oligomers. Thus, the LUMO energy levels become more stabilized for co-oligomers having more acceptor moieties and the HOMO-LUMO energy gap is reduced, therefore, the improvement of the conduction properties of these species is, then, observed. Moreover, the absorption spectra, computed in the presence or not of solvent at PCM model in chloroform, shows that the increase of acceptor character induces a red shift and important absorption intensity. The decrease injection barrier and smaller reorganization energies are revealing that our designed co-oligomers would be an efficient hole as well as electron transfer materials. The predicted values have shown that the designed derivatives would be efficient for the organic field effect transistors, photovoltaics and light emitters.