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Adjusting the Local Arrangement of ?-Stacked Oligothiophenes through Hydrogen Bonds: A Viable Route to Promote Charge Transfer.

ABSTRACT: We show that substituting quaterthiophene cores with strong H-bond aggregators, such as urea groups, provides an efficient way to adjust the mutual in-plane displacements of the semiconducting units and promote charge transfer. Our 2-D structure-property mapping reveals that the insertion of substituents induces up to 2.0 Å longitudinal and transversal displacements between the ?-conjugated moieties. Some of these relative displacements lead to improved cofacial orbital overlaps that are otherwise inaccessible due to Pauli repulsion. Our results also emphasize that the fine-tuning of in-plane displacements is more effective than achieving "tighter" packing to promote charge-transfer properties.

SUBMITTER: Liu H

PROVIDER: S-EPMC4598018 | biostudies-literature | 2014 Jul

REPOSITORIES: biostudies-literature

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Adjusting the Local Arrangement of π-Stacked Oligothiophenes through Hydrogen Bonds: A Viable Route to Promote Charge Transfer.

Liu Hongguang H Brémond Éric É Prlj Antonio A Gonthier Jérôme F JF Corminboeuf Clémence C

The journal of physical chemistry letters 20140620 13

We show that substituting quaterthiophene cores with strong H-bond aggregators, such as urea groups, provides an efficient way to adjust the mutual in-plane displacements of the semiconducting units and promote charge transfer. Our 2-D structure-property mapping reveals that the insertion of substituents induces up to 2.0 Å longitudinal and transversal displacements between the π-conjugated moieties. Some of these relative displacements lead to improved cofacial orbital overlaps that are otherwi ...[more]

PMID: 26279553

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Project description:Oligothiophenes incorporating MM quadruple bonds have been prepared from the reactions between Mo(2)(TiPB)(4) (TiPB = 2,4,6-triisopropyl benzoate) and 3',4'-dihexyl-2,2'-:5',2''-terthiophene-5,5''-dicarboxylic acid. The oligomers of empirical formula Mo(2)(TiPB)(2)(O(2)C(Th)-C(4)(n-hexyl)(2)S-(Th)CO(2)) are soluble in THF and form thin films with spin-coating (Th = thiophene). The reactions between Mo(2)(TiPB)(4) and 2-thienylcarboxylic acid (Th-H), 2,2'-bithiophene-5-carboxylic acid (BTh-H), and (2,2':5',2''-terthiophene)-5-carboxylic acid (TTh-H) yield compounds of formula trans-Mo(2)(TiPB)(2)L(2), where L = Th, BTh, and TTh (the corresponding thienylcarboxylate), and these compounds are considered as models for the aforementioned oligomers. In all cases, the thienyl groups are substituted or coupled at the 2,5 positions. Based on the x-ray analysis, the molecular structure of trans-Mo(2)(TiPB)(2)(BTh)(2) reveals an extended Lpi-M(2)delta-Lpi conjugation. Calculations of the electronic structures on model compounds, in which the TiPB are substituted by formate ligands, reveal that the HOMO is mainly attributed to the M(2)delta orbital, which is stabilized by back-bonding to one of the thienylcarboxylate pi* combinations, and the LUMO is an in-phase combination of the thienylcarboxylate pi* orbitals. The compounds and the oligomers are intensely colored due to M(2)delta-thienyl carboxylate pi* charge transfer transitions that fall in the visible region of the spectrum. For the molybdenum complexes and their oligomers, the photophysical properties have been studied by steady-state absorption spectroscopy and emission spectroscopy, together with time-resolved emission and transient absorption for the determination of relaxation dynamics. Remarkably, THF solutions the molybdenum complexes show room-temperature dual emission, fluorescence and phosphorescence, originating mainly from (1)MLCT and (3)MM(deltadelta*) states, respectively. With increasing number of thienyl rings from 1 to 3, the observed lifetimes of the (1)MLCT state increase from 4 to 12 ps, while the phosphorescence lifetimes are approximately 80 micros. The oligomers show similar photophysical properties as the corresponding monomers in THF but have notably longer-lived triplet states, approximately 200 micros in thin films. These results, when compared with metallated oligothiophenes of the later transition elements, reveal that M(2)delta-thienyl pi conjugation leads to a very small energy gap between the (1)MLCT and (3)MLCT states of <0.6 eV.

Dataset Information

Adjusting the Local Arrangement of ?-Stacked Oligothiophenes through Hydrogen Bonds: A Viable Route to Promote Charge Transfer.

Publications

Adjusting the Local Arrangement of π-Stacked Oligothiophenes through Hydrogen Bonds: A Viable Route to Promote Charge Transfer.

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