Photocatalyzed Oxidative Tandem Reaction Mediated by Bipyridinium for Multifunctional Derivatization of Alcohols.

The multifunctional derivatization of alcohols has been achieved by the bipyridinium-based conjugated small molecule photocatalysts with redox center and Lewis acid site. Besides exhibiting high activity in the selective generation of aldehydes/ketones, acids from alcohols through solvent modulation, this system renders the first selective synthesis of esters via an attractive cross-coupling pattern, whose reaction route is significantly different from the traditional condensation of alcohols and acids or esterification from hemiacetals. Following the oxidization of alcohol to aldehyde via bipyridinium-mediated electron and energy transfer, the Lewis acid site of bipyridinium then activates the aldehyde and methanol to obtain the acetal, which further reacts with methanol to generate ester. This method not only demonstrates a clear advantage of bipyridinium in diverse catalytic activities, but also paves the way for designing efficient multifunctional small molecule photocatalysts. This metal- and additive-free photocatalytic esterification reaction marks a significant advancement towards a more environmentally friendly, cost-effective and green sustainable approach, attributed to the utilization of renewable substrate alcohol and the abundant, low-cost air as the oxidant. The mildness of this esterification reaction condition provides a more suitable alternative for large-scale industrial production of esters.

One-pot Tandem Synthesis and Spontaneous Product Separation of N-heterocycles based on Bifunctional Small-molecule Photocatalyst.

Homogeneous and heterogeneous reactions wherein the resulting products remain dissolved in solvents generally require complicated separation and purification process, despite the advantage of heterogeneous systems allowing retrieval of catalysts. Herein, we have developed an efficient approach for the one-pot tandem synthesis of quinazolines, quinazolinones and benzothiadiazine 1,1-dioxides from alcohols and amines utilizing a bifunctional bipyridinium photocatalyst with redox and Lewis acid sites using air as an oxidant. Through solvent-modulation strategy, the photocatalytic system exhibits high performance and enables most products to separate spontaneously. Consequently, the homogeneous catalyst can be reused by direct centrifugation isolation of the products. Notably, the method is also applicable to the less active substrates, such as heterocyclic alcohols and aliphatic alcohols, and thus provides an efficient and environmentally friendly photocatalytic route with spontaneous separation of N-heterocycles to reduce production costs and meet the needs of atomic economy and green chemistry.

Photomechanical behavior triggered by [2 + 2] cycloaddition and photochromism of a pyridinium-functionalized coordination complex.

Photoinduced bending behavior triggered by [2 + 2] cycloaddition of a photoactive complex has been successfully achieved, accompanied by photochromic and fluorescence changes that provide convenience for long-distance observation of photomechanical motion. The key design feature is based on the introduction of flexible methylene groups and cation-π interactions. Moreover, the potential application in photomechanical devices was reflected by bending and supporting force experiments on the complex composite film, which is of increasing importance especially in soft actuators and robots.

Synergism of photocycloaddition and photoinduced electron transfer for multi-state responsive materials with high-stability and reversibility.

A dual-photoresponsive coordination polymer displaying color-distinguishable olefin/cyclobutane-linked pyridinium radical states through photoinduced electron transfer and photocycloaddition has been successfully assembled based on the monoquaternized trans-1,2-bis(4-pyridyl)ethylene and electron-rich benzenetetra-carboxylate anion. The synergy of charge-transfer and cation-π interactions within the framework endows the compound with excellent stability toward high temperature (350 °C), acidic/basic environments (pH = 2-12) and organic solvents. Reversible recovery from the radical states to their initial states, and reverse-cyclization can be achieved upon heat-treatment.