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Changes in color are one of the most obvious and easily followed responses that can be induced by an external stimulus. π-Conjugated organophosphorus compounds are on the rise to challenge established systems by opening up new and simple pathways to diversely modified optoelectronic properties--the main challenge for the development of new chromic materials. Relevant stimuli highlighted in this Frontier article include electronic current (electrochromism), light (photochromism), solvent polarity (solvatochromism), aggregation formation (aggregation induced emission, AIE), mechanical force (mechanochromism), temperature (thermochromism), organic solvent vapor (vapochromism), and pH (halochromism).

A simple and representative procedure for the synthesis of N,N′-diarylated phosphaviologens directly from both electron-rich and electron-poor diaryliodonium salts and 2,7-diazadibenzophosphole oxide is reported. The latter are electron-deficient congeners of the widely utilized N,N′-disubstituted 4,4′-bipyridinium cations, also known as viologens, that proved to be inaccessible by the classical two-step route. The single-step preparation method for phosphaviologens described herein could be extended to genuine viologens but reached its limit when sterically demanding diaryliodonium salts were used. The studied phosphaviologens feature a significantly lowered reduction threshold as compared to all other (phospha)viologens known to date due to the combination of an extended π-system with an electron deficient phosphole core. In addition, a considerably smaller HOMO–LUMO gap was observed due to efficient π-delocalization across the phosphaviologen core, as well as the N-aryl substituents, which was corrobor...

ConspectusThe development of conjugated organic materials has become a rapidly evolving field of research, particularly with a view toward practical applications in so-called organic electronics that encompass a variety of device types, such as OLEDs, OPVs, and OFETs. Almost all of these devices minimally require the presence of electron-donor and -acceptor components that act as p- and n-type semiconductors, respectively. Research over the past two decades has shown that while there is an abundant resource of organic p-type materials, suitable n-type species are few and far between. To overcome this severe bottleneck for the further development of organic electronics, researchers have identified organo-main-group avenues as valuable alternatives toward organic electron-acceptor materials that may ultimately be used as n-type components in practical devices. One particular element of interest in this context is phosphorus, which at first glance may not necessarily suggest such properties.In this Account, ...

In this account, we describe our efforts in developing the chemistry of the highly luminescent dithieno[3,2-b:2′,3′-d]phosphole system over the last ten years. We provide an overview of the synthetic possibilities and the inherent tunability of the emission properties offered by this particular heterole. 1 Introduction 2 Synthesis and Properties of Dithieno[3,2-b:2′,3′-d]phospholes 3 Functionalization of Dithieno[3,2-b:2′,3′-d]phospholes 3.1 Phosphorus Functionalization 3.2 Functionalization at the 2- and 6-Positions 3.2.1 Symmetric Functionalization 3.2.2 Asymmetric Functionalization 3.3 Incorporation of Fused Rings onto the Main Scaffold 4 Photophysical Properties 5 Conclusions

Phosphole-based π-conjugated compounds have recently attracted significant attention due their unique electronic properties. It is now well established that the versatile phosphorus chemistry offers great opportunities for efficient fine-tuning of the properties of π-conjugated systems from a fundamental point of view; a feature that pure carbon-based π-conjugated materials cannot provide. This perspective highlights the recent progress using phosphole-based π-conjugated building blocks towards applied materials with multiple and diverse functionalities.

The introduction of phosphorus-containing moieties into π-conjugated thiophene materials has been found to provide materials with strongly optimized and highly tunable optoelectronic features compared to their native thiophene counterparts. 2,5-Diaryl- and 2,5-bis(heteroaryl)phospholes as well as fused tricyclic dithieno[3,2-b:2′,3′-d]phospholes represent two very valuable building blocks for organic electronics as their intriguing features can be altered systematically by several, in part unique, methodologies. The potential scope of these modifications has been determined by comprehensive investigations of their structure–property relationships via suitable molecular model compounds. Onseveral occasions, these observations could successfully be transposed to corresponding polymers that are often difficult to characterize independently. The same is true for the first organic light-emitting diodes (OLEDs) based on a phosphole scaffold, whose properties could also be predicted successfully. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)