Excited-state engineering of oligothiophenes via phosphorus chemistry towards strong fluorescent materials.

Due to efficient intersystem crossing (ISC), combined with efficient non-radiative processes of the triplet excited state, oligothiophenes generally exhibit very weak photoluminescence. Phosphorus (P)-bridged terthiophenes (P-terThs) and phosphorus (P)-bridged bithiophenes (P-biThs) were synthesized. The diverse and well-defined P-chemistry has been applied to fine tune the photophysical properties of these materials. The asymmetric electronic coupling between the P-center and terThs suppressed the electronic interactions of two terTh and biTh moieties in the ground state S0. Particularly, P-terThs and P-biThs having a positively charged P(+)-center induce pronounced asymmetric electronic environments on the two terThs and two biThs, respectively, which allows relaxation from the initial excited state via symmetry breaking charge transfer (SBCT) to give the charge separated state SSBCT. P-terThs and P-biThs having a positively charged P(+)-center exhibit stronger SBCT than others, which may result in a weaker ISC of oligothiophenes, and consequently lead to the photoluminescence quantum yields (PLQYs) being as high as 71% and 39%, respectively. The current study uncovered detailed insights on the effects of phosphorus chemistry on the SBCT of oligothiophenes and their resulting effects on the photophysical properties of P-bridged oligothiophenes, which have not been previously addressed in oligothiophenes.

Amorphous porous organic polymers containing main group elements.

Amorphous porous organic polymers (aPOPs) are a type of highly crosslinked polymers. These polymers are generally constructed from rigid organic building blocks, which have become an important subclass of POPs with diverse applications. In the early stage of development, a wide range of carbon-based building blocks and network forming chemistry afforded a large library of aPOPs with rich structures and properties. Recently, implanting main group elements with diverse geometric structures and electronic configurations into aPOPs has proven to be a useful tool to fine-tune the structures and properties of these polymers. Herein, we outline the recent advances in the field of main group (MG)-aPOPs where main-group elements either played unique roles in tuning the structures and properties of MG-aPOPs, or offered new strategies in the synthesis of MG-aPOPs. Furthermore, this Review discusses various challenges remaining in the field from the perspectives of synthetic strategies and characterization techniques, and presents some specific studies that may potentially address the challenges.

Stille type P-C coupling polycondensation towards phosphorus-crosslinked polythiophenes with P-regulated photocatalytic hydrogen evolution.

Recently, exploring new type polymerization protocols has been a major driving force in advancing organic polymers into highly functional materials. Herein we report a new polycondensation protocol to implant the phosphorus (P) atom in the main backbone of crosslinked polythiophenes. The polycondensation harnesses a Stille phosphorus-carbon (P-C) coupling reaction between phosphorus halides and aryl stannanes that has not been reported previously. Mechanistic studies uncovered that the P-electrophile makes the reactivity of a catalytic Pd-center highly sensitive towards the chemical structures of aryl stannanes, which is distinct from the typical Stille carbon-carbon coupling reaction. The efficient P-C polycondensation afforded a series of P-crosslinked polythiophenes (PC-PTs). Leveraging on the direct P-crosslinking polymerization, solid-state 31P NMR studies revealed highly uniform crosslinking environments. Efficient post-polymerization P-chemistry was also applied to the PC-PTs, which readily yielded the polymers with various P-environments. As a proof of concept, new PC-PTs were applied as the photocatalysts for H2 evolution under visible light irradiation. PC-PTs with an ionic P(Me)-center exhibit a H2 evolution rate up to 2050 µmol h-1 g-1, which is much higher than those of PC-PTs with a P(O)-center (900 µmol h-1 g-1) and P(iii)-center (155 µmol h-1 g-1). For the first time, the studies reveal that regulating P-center environments can be an effective strategy for fine tuning the photocatalytic H2 evolution performance of organic polymers.

Synthesis and Characterizations of Polythiophene Networks with Nonplanar BN Lewis Pair Building Blocks.

Doping the boron (B) element endowed organic π-conjugated polymers (OCPs) with intriguing optoelectronic properties. Herein, we introduce a new series of thienylborane-pyridine (BN) Lewis pairs via the facile reactions between thienylborane and various pyridine derivatives. Particularly, we developed a "one-pot" synthetic protocol to access BN2 with an unstable 4-bromopyridine moiety. Polycondensations between the BN Lewis pairs and distannylated thiophene afforded a new series of BN-cross-linked polythiophenes (BN-PTs). Experiments revealed that BN-PTs exhibited highly uniform chemical structures, particularly the uniform chemical environment of B-centers. BN-PTs showed good stability in the solid state. PBN2 even maintained the uniform B-center under high temperature or moisture conditions. The studies further suggested that the presence of topological BN structures endowed the polymers with strong intramolecular charge separation character. As a proof of concept, a representative BN-PT was tested as the catalyst for photocatalytic hydrogen evolution.