Optoelectronic Properties of High Triplet σ–π-Conjugated Poly[(biphenyl group IV-A atom (C, Si, Ge, Sn)] Backbones

Abstract

A series of σ–π-conjugated polymers composed of biphenyl and X atom as backbone repeat unit (where X is the group IV-A atom: carbon, silicon, germanium, or tin) grafted with two alkoxy-substituted biphenyls at the X atom as side chains are synthesized and their optoelectronic properties are studied systematically. We choose biphenyl rather than alkyl as the side chain because its frontier molecular orbital distributions are close to those of our previously reported σ–π-conjugated polymer grafted with transport moieties. The present σ–π polymers with various X atoms show significant differences in triplet energy (E T) ranging from 2.58 to 2.83 eV with the sequence Ge > Si > C > Sn and in charge mobilities from 10–9 to 10–7 cm2/(V s) with the sequence Si > Ge > Sn > C, indicating that the properties of the σ–π polymers are largely affected by their X atoms. The Ge- and Sn-based σ–π-conjugated polymers show the highest and lowest E T values, respectively, due to their different levels of π-electron delocalization caused by size effects and (d–p)­π orbital interaction. For their charge transport properties, the Si-based conjugated σ–π polymer gives the highest hole and electron mobilities due to the stronger σ–π conjugation and shorter Si–C bond length between the attached carbon atom in biphenyl and Si. On the contrary, the C-based σ–π-conjugated polymer gives the lowest charge mobilities due to a lack of d orbital in the C atom leading to a poor σ–π conjugation characteristic. These σ–π polymers with different E T levels and charge transport properties show a significant effect on their electroluminescence characteristics. Among them, the Ge-based σ–π-conjugated polymer when used as host shows the best device performance due to its higher E T and reasonable charge mobility. Such findings of different optoelectronic properties of these σ–π-conjugated polymers provide useful guidelines for the selection of backbone for designing σ–π-conjugated polymer host grafted with charge transport moieties.

Metal–Organic Frameworks with Zero and Low‐Valent Metal Nodes Connected by Tetratopic Phosphine Ligands

“…It is therefore remarkable that the two materials display drastically different rates of decomposition in air. The enhanced resistance to oxidation of Sn2 ‐ Pd suggests a difference in the donor/acceptor properties of Si2 and Sn2 [19] . The central atom of the phosphine thus appears to play a significant role in determining the strength of the associated metal–phosphine bonds.…”

Realizing highly efficient blue photoluminescence of dimethylsilane-aryl (phenylene, diphenylene, fluorenyl) main-chain polymers with σ–π conjugation

“…28,29 With regard to high quantum efficiency, strong blue emission and charge carrier mobility in highly ordered assemblies, aromatic derivatives with p-conjugated fragments (phenylene, diphenylene, fluorene, pyrene or anthracene derivatives) have been intensively investigated and regarded as the most promising blue-emitting materials. 12,[30][31][32][33] Generally, aromatic groups possess a rigid planar structure, which can minimize their vibrational energy levels to afford high color purity, as well as offer stable thermal and electrochemical properties. 23 Nevertheless, such a structure with a face-to-face parallel stacking easily causes Haggregation by intermolecular p-p interactions.…”

“…As π-conjugated aromatic groups with excellent optical properties are introduced into the main chain of organosilicon polymers, electrons can be delocalized along the main chain by efficient d-orbital participated σ–π conjugations between Si atoms and π units. 30,37 The final products with large extent of σ–π conjugations derived from superior charge injection and transport of the main chain exhibit distinguished fluorescence performances. 39,40 The basis of this technology is to introduce aryl groups with excellent fluorescence properties into the –Si–C– backbone via the Grignard reaction and yield an organosilicon polymer with alternating π-conjugated units.…”

Dual-photofunctional organogermanium compound based on donor–acceptor–donor architecture

“…3 In sharp contrast, the utilization of organogermanium compounds and polymers as optoelectronic materials has been rarely exploited. 4–6 For example, tetraaryl germanes and related polymers have been used as host materials for organic light-emitting diodes (OLEDs), by utilizing the high triplet energy and adequate carrier transport capability. 4 Also, a systematic study of blue-emitters based on phenothiaborin-connected acridan analogues with group 14 elements including germanium for non-doped efficient OLEDs has been reported.…”

“…4–6 For example, tetraaryl germanes and related polymers have been used as host materials for organic light-emitting diodes (OLEDs), by utilizing the high triplet energy and adequate carrier transport capability. 4 Also, a systematic study of blue-emitters based on phenothiaborin-connected acridan analogues with group 14 elements including germanium for non-doped efficient OLEDs has been reported. 5 Given unique characteristics of organogermanes such as a large atomic radius (122 pm), electropositive nature ( χ p = 2.01), and capability of σ–π conjugation, the development of novel Ge-containing organic functional materials would offer us great opportunities to cultivate design principles for a new class of functional materials.…”