Selective Tuning of the Band Gap of π‐Conjugated Dithieno[3,2‐b:2′,3′‐d]phospholes toward Different Emission Colors

Abstract

The systematic extension of the pi-conjugated system of strongly blue-luminescent dithieno[3,2-b:2',3'-d]phospholes has been investigated with the goal of obtaining different emission colors. Functionalization of the 2- and 6-position of the dithienophosphole scaffold with halogen substituents provided functional building blocks for subsequent cross-coupling experiments with various homo- and heteroaryls to selectively decrease the band gap of the materials. By this strategy materials with different emission colors ranging from green via yellow to orange could be obtained. This feature supports their suitability for organic light-emitting diodes with respect to an application in full-color flat-panel displays. The experimental results were nicely supported by theoretical DFT calculations providing a deeper understanding of the electronic structure in the extended materials, and also allowing for the design of future materials based on a dithienophosphole core. Furthermore, the phosphorus center in the extended molecular materials can efficiently be fine-tuned in subsequent simple chemical functionalizations. This allows for a tailoring of the optoelectronic properties of the extended dithienophospholes to suit the requirements of potential applications.

Simple and Efficient Generation of White Light Emission From Organophosphorus Building Blocks

“…The latter emission color can be generated by extending the pconjugation of the scaffold with 4-aminophenyl groups. [12] For improved solubility, and to verify the general suitability of our approach, we first targeted a simple P-phenyl-substituted, N,Ndimethylamino extended species for this study. However, with the ultimate synthesis of the corresponding styrene material in mind, a modification of the synthesis towards extended dithienophospholes was deemed necessary; usually, extended systems are synthesized by Suzuki-Miyaura or Stille cross-coupling of a 2,6-dibromodithienophosphole with aryl-boronates or -stannanes (Scheme 1, top).…”

“…However, with the ultimate synthesis of the corresponding styrene material in mind, a modification of the synthesis towards extended dithienophospholes was deemed necessary; usually, extended systems are synthesized by Suzuki-Miyaura or Stille cross-coupling of a 2,6-dibromodithienophosphole with aryl-boronates or -stannanes (Scheme 1, top). [12] Notably, this could potentially lead to an undesired premature polymerization of the styrene functionality during the cross-coupling process. For this reason, we developed an ''inverse'' synthesis of the extended species 5/6, in which the aminophenyl groups are introduced first to provide an extended 2,2 0 -bithiophene that can then be converted into the corresponding phosphole (Scheme 1B): Selective Suzuki-Miyaura cross-coupling of 3,3 0 ,5,5 0 -tetrabromo-2,2 0 -bithiophene 3 [13] with 4-(N,N-dimethylamino)phenylpinacolborane provided the extended bithiophene 4 after 72 h in refluxing tetrahydrofuran (THF) (catalyst (cat.)…”

“…Furthermore, the photophysical properties of the core can efficiently be modified through a variety of options including modification of the phosphorus center (A; E ¼ lone pair, O, S, BH 3 , Me þ , [M]), and the main scaffold at the 2,6-positions; [11] in a recent study, we reported the tuning of the emission color from green to orange by extending p-conjugation of the dithienophosphole core with different aryl groups (e.g., R 2 ¼ Ph, 2-thienyl, 4-(N,N-diphenylamino)phenyl). [12] Since the unprecedented strong emission properties of dithienophospholes provide an excellent base for this approach, This paper describes a structure-property study using two dithieno [3,2-b;2(,3(-d]phosphole building blocks for the generation of white light emission and the incorporation of these units in a single polystyrene material. The emission of one of the light-emitting organophosphorus building blocks can efficiently be switched from orange to green by simple protonation of the amino functional groups that are part of the p-conjugated scaffold.…”

2,6-Bis(tributyltin)benzo[1,2-b:5,4-b’]dithiophene: a new synthon for organic semiconductors

“…We have also observed this structural feature in an earlier study involving phosphorusbased oligothiophenes. 26 Notably, the frontier orbitals of 9 are also well distributed over the whole molecule. As can been seen further, the LUMO in 2 and 7-9 has a similar shape of all four compounds, however, extended throughout the cross-coupled sections in 7-9.…”

Fused thiophenes: an overview of the computational investigations

“…69,70 New thienoacene-based organic semiconductors possessing benzothiophene showed very high mobility exceeding 10 cm 2 s −1 V −1 , which could be expected to expand horizons of organic semiconductors. 71 Thiophene-based fused heteroacenes containing different heteroatoms such as -silole, 72,73 -borole, 74,75 and -phosphole 76,77 have also received considerable attention as key components of organic materials for construction of optical and electronic devices.…”