Pluripotent Features of Doubly Thiophene‐Fused Benzodiphospholes as Organic Functional Materials

Abstract

Linear ladder‐type π‐conjugated molecules have attracted much interest because of their intriguing physicochemical properties. To modulate their electronic structures, an effective strategy is to incorporate main‐group elements into ladder‐type π‐conjugated molecules. In line with this strategy, a variety of ladder‐type π‐conjugated molecules with main‐group elements have been synthesized to explore their potential utility as organic functional materials. In this context, phosphole‐based π‐conjugated molecules are highly attractive, owing to their unique optical and electrochemical properties, which arise from the phosphorus atom. Herein, the synthesis and physicochemical properties of doubly thiophene‐fused benzodiphospholes, as a new class of phosphole‐based ladder‐type π‐conjugated molecule, are reported. Systematic investigations into the physicochemical properties of doubly thiophene‐fused benzodiphospholes revealed their pluripotent features: intense near‐infrared fluorescence, excellent two‐photon absorption property, and remarkably high electron‐transporting ability. This study demonstrates the potential utility of doubly thiophene‐fused benzodiphospholes as organic functional materials for biological imaging, nonlinear optics, organic transistors, and organic photovoltaics.

Thiophene‐Fused Naphthodiphospholes: Modulation of the Structural and Electronic Properties of Polycyclic Aromatics by Precise Fusion of Heteroles

“…The Suzuki‐Miyaura coupling of 5 with 2,3‐dibromothiophene gave thienylnaphthalene 6 as a key precursor for 1 . Treatment of 6 with n ‐BuLi followed by the addition of dichlorophenylphosphine and H 2 O 2 provided 1‐ trans and 1‐ cis as a diastereomeric mixture [17] . These diastereomers were easily separated by silica‐gel column chromatography to give 1‐ trans in 19 % and 1‐ cis in 21 % yield.…”

“…[b] The samples were excited at 367 nm for 1‐ trans / cis and at 415 nm for 2‐ trans / cis and 3‐ trans / cis . [c] Absolute fluorescence quantum yields ( Φ F ) were determined using thiophene‐fused benzodiphosphole ( Φ F =0.91) as a standard [17] . [d] Optical HOMO‐LUMO gaps from the intersection of normalized absorption and fluorescence spectra.…”

“…To date, various fused phosphole derivatives have been actively investigated due to their high electron‐transporting ability [13] and intense emission [14] . In this context, a variety of polycyclic aromatics with both sulfur and phosphorus atoms have been developed and exhibited both features [15–18] . However, placing different heteroatoms (i. e., sulfur and phosphorus) precisely in the same π‐frameworks is still a challenge.…”

“…In this regard, we expected that introducing two phosphorus atoms into polycyclic aromatics precisely would provide an assortment of isomers originated from not only the position and orientation of the phosphole rings, but also the orientation of substituents on the phosphorus atoms ( trans / cis configurations) (Figure 2). Very recently, we demonstrated the potential utility of thiophene‐fused benzodiphospholes as organic functional materials for various purpose [17] . Precisely controlled fusion of heteroles into an aromatic core could be a useful approach to uncover their intrinsic properties that may create the possibility of new applications as organic functional materials.…”

“…[14] In this context, a variety of polycyclic aromatics with both sulfur and phosphorus atoms have been developed and exhibited both features. [15][16][17][18] However, placing different heteroatoms (i. e., sulfur and phosphorus) precisely in the same π-frameworks is still a challenge.…”