Theoretical study of the effect of ethynyl group on the structure and electrical properties of phenyl-thiadiazole systems as precursors of electron-conducting materials

Abstract

2,5-Bis(phenylethynyl)-1,3,4-thiadiazole (PhEtTh) and 2,5-diphenyl-1,3,4-thiadiazole (PhTh) are expected to be building blocks for polymer materials that could be employed to conduct electricity due to their narrow highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps. In this work, a theoretical, comparative study about the effect of the ethynyl group on the planarity and electrical conductivity of this kind of systems has been carried out. Thus, several ab initio (Hartree-Fock, Moller-Plesset) and DFT (B3LYP, B3PW91, M05, M05-2X) methods and basis sets (6-31G(*), 6-31G+G(**), 6-311G(**), cc-pVDZ, cc-pVTZ) have been tested. As a result, PhEtTh showed better properties for its use as electric conducting material relative to PhTh due to its smaller HOMO-LUMO gap, as well as its enhanced trend to retain the planarity provided the reduction in steric hindrances that the ethynyl group (-C[triple bond]C-) permits. Solvent effects were also modeled for ethanol and chloroform under the conductor-like polarizable continuum model approximation. Finally, electronic transitions in gas and solution phases were predicted by using TDDFT approximation in order to compare the theoretical lambda(max) with the experimental values reported in literature for both compounds.

Cation–π and anion–π interactions

“…The effect of the ethynyl group on the structure and electrical properties of phenyl–thiadiazole systems has been studied theoretically 133. Moreover, the effect of ethynyl substitution on the ion–π binding ability of benzene has been recently analyzed 134.…”

Optoelectronic and Semiconducting Properties of Conjugated Polymers Composed of Thiazolo[5,4-d]thiazole and Arene Imides Linked by Ethynylene Bridges

“…5,6 During the last years, we have investigated the molecular structure and electronic properties of series of PAEs containing Th as electron-accepting group linked to phenylene and -C≡C-bridges by means of Density Functional Theory (DFT) calculations. [19][20][21][22][23] Their interesting electronic properties make them suitable candidates for their use as organic semiconductors. Going one step further, thiazolo [5,4- …”

“…[5][6][7][8] Different research groups have investigated the use of PAEs and hyperbranched PAEs as molecular wires, OLEDs, OSCs, OTFTs and fluorescent chemical sensors. [9][10][11][12][13][14] The interesting electronic properties exhibited by PAEs can be related to the axial symmetry of ethynylene groups, which allows to maintain the conjugation (note that between adjacent aryl groups at different relative orientations rotational barriers are as small as 1 kcal mol -1 in these cases) [15][16][17][18][19][20] across the whole molecular backbone.…”

Bis(arylene-ethynylene)-s-tetrazines: A Promising Family of n-Type Organic Semiconductors?

“…17 The increase in the delocalization of the LUMO orbital could be achieved by the introduction of ethynylene groups (-C≡C-) as a bridge between the three aromatic rings; in fact the ethynylene group, due to its axial symmetry, could allow to extend the conjugation to adjacent arylene groups. [27][28][29][30][31][32] Note also that the actual synthesis of s-tetrazine ethynylene derivatives is possible through cross-coupling reactions on some s-tetrazine compounds (compounds a and b in Chart 1), as shown by Novák and Kotschy, 33 though we are not aware of any attempt for (ArCC) 2 Tz compounds.…”