The role of relativity and dispersion controlled inter-chain interaction on the band gap of thiophene, selenophene, and tellurophene oligomers

Abstract

Ab initio relativistic density functional theoretical calculations have been carried out on π-conjugated oligomers of increasing length with S, Se, and Te as heteroatoms. The band gap of the corresponding polymers has been obtained by plotting lowest unoccupied molecular orbital (LUMO)-highest occupied molecular orbital (HOMO)gap against the reciprocal of the number of monomer units (1/N) and extrapolating the curve to 1/N = 0. With B3LYP functional, we predict that role of relativistic correction terms is not very significant in the determination of final band gap of thiophene, selenophene, and tellurophene polymer. The origin of this observation is provided through the density of states (DOS) analysis which manifests that DOS contribution across the Fermi level of these polymers is mostly governed by C atoms and as a consequence relativistic correction terms due to heavy heteroatom remain insignificant to the band gap modification. We also inspected the role of inter-chain interaction in determining the net LUMO-HOMO gap of π-stacked double chain oligomers of increasing length. We have found that due to the exciton splitting in the stacked configurations, the LUMO-HOMO gap decreases steadily. Furthermore, we have noticed that dispersion force has important role in the reduction of the LUMO-HOMO gap of the oligomers studied.

The Synthesis and Optoelectronic Applications for Tellurophene‐Based Small Molecules and Polymers

“…[2] The calculated geometry of tellurophenes are highly planar because of its shortest intra-ring CÀ C bond comparing to thiophene and selenophene ones, [3] thus the narrowest optical bandgaps can be inferred. [4] Experimentally, the HOMO-LUMO gaps for polychalcogenophenes are changing from 2.0 eV for polythiophene, 1.9 eV for poly-selenophene to 1.5 eV for polytellurophene, [5] which is in good agreement with the theoretical predictions of 2.06 eV, 1.85 eV and 1.48 eV, respectively. [4,6] Besides, the intra-ring CÀ C bond length in tellurophene oligomer is the shortest one (1.440 Å), which indicate that the tellurophene may possess the greatest quinoid characteristics.…”

“…[4] Experimentally, the HOMO-LUMO gaps for polychalcogenophenes are changing from 2.0 eV for polythiophene, 1.9 eV for poly-selenophene to 1.5 eV for polytellurophene, [5] which is in good agreement with the theoretical predictions of 2.06 eV, 1.85 eV and 1.48 eV, respectively. [4,6] Besides, the intra-ring CÀ C bond length in tellurophene oligomer is the shortest one (1.440 Å), which indicate that the tellurophene may possess the greatest quinoid characteristics. Furthermore, tellurophene-based conjugated systems often demonstrate high intermolecular heteroatom-heteroatom interactions since they usually possess large tellurium heteroatoms.…”

“…Generally, the substitution of heteroatoms can significantly change the physicochemical properties of aromatic systems. [4,6] Besides, the intra-ring CÀ C bond length in tellurophene oligomer is the shortest one (1.440 Å), which indicate that the tellurophene may possess the greatest quinoid characteristics. [2] The calculated geometry of tellurophenes are highly planar because of its shortest intra-ring CÀ C bond comparing to thiophene and selenophene ones, [3] thus the narrowest optical bandgaps can be inferred.…”

Poly(3-alkyltellurophene)s Are Solution-Processable Polyheterocycles

“…7 The energy of the low energy singlet states of the pentamer will be higher than a polymer but can be used to identify the orbitals involved in the transitions. [8][9][10] The calculated Uv-vis spectrum was generated from the TD-DFT data with Gausview 11 by applying a gaussian function with 0.33 eV peak half width at half height placed on each transition.…”

TD-DFT Simulation and Experimental Studies of a Mirrorless Lasing of Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)]

“…CPs consist of a large number of atoms; hence, the simulation of CPs is considered to be challenging. Thus, many studies have adopted an oligomeric model of the compound [ 35 , 36 , 37 ]. The absorption spectra and energy gap of the PF-co-MEH-PPV were simulated with three monomer units (n = 3) based on the HOMO-LUMO energy gap calculations.…”