Molecular Engineering of the Physical Properties of Highly Luminescent π-Conjugated Phospholes

Abstract

The syntheses as well as detailed studies on the thermal, photophysical, and self-organization properties of a new series of phosphole-based ladder-type materials with exocyclic 5-alkylthienyl substituents are reported. The studies also include DFT calculations that provide support for the experimentally determined photophysics. In contrast to the related “phosphole-lipids” with fused conjugated head that exhibit low luminescence in solution but high luminescence in the solid state, the new system is highly luminescent in both solution and the solid state. The extensive structure–property study reported herein revealed that the physical properties of the new species can significantly be tuned via the size of the conjugated system of the head group, the functionalization of the phosphorus center, as well as the length of the thiophene-appended alkyl chain that impacts the intermolecular interactions via π–π stacking, ionic, and van der Waals interactions, respectively. This molecular engineering approach allows to access materials with intriguing properties that range from highly emissive oils to self-organized one-dimensional fibers.

P‐Terthienyl‐Functionalized Dithieno[3,2‐b:2′,3′‐d]phospholes

“…It should be noted that, as commonly observed for thiophene‐based species, the P ‐thienyl group is disordered. The bond lengths and angles of 3b are in line with those of 6 14. The only noteworthy deviation lies in the C3–P1–C9 angle of 102.85(14)°, which is significantly smaller than the corresponding angle in its H relative 6 [cf.…”

“…Subsequently, oxidation with an excess amount of H 2 O 2 was performed and followed by purification using column chromatography to obtain the environmentally stable compounds 3a , 4 , and 5 in moderate yields of 63, 50, and 54 %, respectively (Scheme ). Compound 3a was obtained as a yellow solid after column chromatography with a 31 P{ 1 H} NMR chemical shift at δ = 12.4 ppm, which is in line with that of 6 and related P ‐(alkyl)thienyl dithienophospholes that exhibit some intriguing self‐assembly properties 14. Compound 4 , containing the linear terthiophene substituent, shows a slight upfield shift at δ 31 P = 11.6 ppm relative to that of 3a , which can be attributed to the increased donor character of the exocyclic substituent; compound 5 , with the branched terthiophene substituent, has a similar upfield shift as 4 at δ 31 P = 11.3 ppm.…”

“…The required 3,3′‐dibromo‐5,5′‐dihexyl‐2,2′‐bithiophene precursor 2a was synthesized according to our previously reported procedure 13c. In addition to the bithienyl precursor, this study also required the corresponding, unknown terthienyl‐substituted dichlorophosphanes; we have reported the 2‐thienyl dichlorophosphane 1T‐PCl 2 very recently14 and the synthesis of the new terthienyl species was adapted from this procedure: Lithiation of the desired oligothiophene derivative with n BuLi, followed by subsequent addition of bis(diethylamino)chlorophosphane afforded the corresponding RP(NEt 2 ) 2 intermediates, which were quenched with HCl to provide the products L3T‐PCl 2 (79 %) and B3T‐PCl 2 (82 %) in good yields. The linear 2,2′:5′,2″‐terthiophene (L3T‐H),15 and the branched 2,2′:3′,2″‐terthiophene‐5,5″‐diylbis(trimethylsilane) (B3T‐H)16 were prepared according to literature procedures.…”

Tuning the aggregation-induced enhanced emission behavior and self-assembly of phosphole-lipids

“…This highly disordered feature was also found in another short-chain-decorated phosphole species in an earlier study. 11 With truncated chain length and enlarged conjugated head group, both the shape anisotropy of the molecule and charge density decrease. Since these forces are integral in the ordering of the compounds in aggregation, decreased shape anisotropy and charge density are likely the cause for the high liquidity of 1b.…”

Synthesis and photophysical properties of novel benzophospholo[3,2-b]indole derivatives

“…For example, dibenzo-fused phospholo[3,2- b ]phosphole dioxides ( Fig. 1 ) [ 25 – 26 ] and benzophosphole-fused tetracyclic heteroacenes, containing boron (B) [ 27 – 29 ], silicon (Si) [ 30 ], oxygen (O) [ 31 ], and sulfur (S) [ 32 – 34 ] ( Fig. 1 ), were synthesized and their physical properties were studied.…”