Electrosynthesis can be easily controlled to achieve high levels of selectivity as a promising green methodology for organic chemistry. It can fulfill several important criteria that are needed to develop environmentally compatible processes. Using electric current as reagent, it can be used to replace toxic or dangerous oxidizing or reducing reagents. The total energy consumption can be reduced and unstable and hazardous reagents can be generated in situ. The reaction at solid-liquid interface can be accelerated by controlling potential and current intensities, while the electrochemistry can simplify the purification and post-treatment processes. We particularly focus on electrochemical synthesis of novel organic electric materials. Special emphasis of our philosophy is that how to understand the polymer synthesis from electrochemical approaches. The most recent information about current research activities of our group can be found in the group's publications, but a brief introduction to each example of recent projects is provided below.
(1) Topology and Sequence Controlled Electropolymerizations
After N-H of carbazole substituted by using hexyl, the chemical and electrochemical oxidative coupling reactions of carbazole ring can be dramatically changed. 9,9'-dihexyl-3,3'-dicarbazyls can be considered to be only product if its oxidative reactions are carried out at low potential (c.a. 1.0 V vs. Ag/Ag+) or in week oxidizer medium (FeCl3). Multiple oligomers and polymers as resulting products appeared in strong oxidizer medium ((NH4)2S2O8) or at high oxidative potential (c.a. > 1.2 V vs. Ag/Ag+). Though oxidative products of carbazols have been widely used, the structural definition has been remaining difficult because their polymers are generally insoluble with inadequate characterizations and unknown dependence of electrochemical potential. We have first provided the effect of oxidative strength on N-alkylcarbazolyl reactions. By utilizing thiscontrollable reaction, we have developed the juntion controlled topological polymerization, which is both chemical and electrochemical radicals initiated step polymerization for synthesis and process of functional polymers.
Fig. 1 Oxidizing strength effect of carbazolyl oxidations.
Fig. 2 Junction-controlled topological polymerization.Angew. Chem. Int. Ed. 57, 4936 (2018). (hot paper)
Fig. 3 Sequnce controlled electropolymerization.Angew. Chem. Int. Ed. 57, 16698 (2018).
(2) Layer by Layer Electropolymerizations
Electrochemical assembly is introduced as a novel fabrication methodology for preparing layered low-doped thin films. This method allows us to covalently immobilize functionalunits (e.g., porphyrin, fullerene, fluorene, semi- and conductive nanoparticles) into thin films having desired thicknesses and designable sequences for both homo- and hetero-assemblies of photoactive multilayers and electrodes while ensuring efficient layer to layer electronic interactions. By utilizing this method, the distribution controllable of nanoparticle in thin film, one-pot layer by layer assembly, and electrochemically fabricated photovoltaic devices were achieved.
Fig. 4 Electrochemical engneering of organic/inorganic hybrid film.Chin. Chem. Lett. 27, 487 (2016); Chem.Commun. 50, 10448 (2014)
(3) Low-doped Electropolymerized Films for Optical Limiting of Laser
Over the past few decades, use of electropolymerization has been limited to applications where ion-doping is required (i.e. electrochromism, conductive films etc.) because non-quantitative (unlimited) electrochemical coupling reactions usually result in conducting conjugated polymers with an unavoidable highly doped state, and the quantitative electrochemical selection of the polymer structure remains challenging. In fact, the resulting conjugated polymers and highly doped states are often unnecessary (or disadvantageous) for a wide library of building blocks. We have developed the low-doped polymers via well-controlled electrochemcial reactions including dimerization of N-alkylcarbazole, pyrene and alkynyl. These films, with amorphous and transparent states, showed significant optical limiting response with an excellent threshold of 63 mJ/cm2.
Fig. 5 Optical limiting of isolated fullerene-rich thin films.ACS App. Mater. Inter. 8, 24295 (2016)；Small 9, 2064 (2013); Adv.Mater. 24, 5727 (2012)
Figure 6. Electroreductive layer by layer assembly for oxidizing-sensitive materials.ACS App. Mater. Inter. 9, 32179 (2017)
National Natural Science Foundation of China
Changchun Institute of Applied Chemistry (CIAC) and CAS