Enhancing stability of diradical polycyclic hydrocarbons via P=O-attaching

Diradical polycyclic hydrocarbons(PHs)have unique open-shell structures and interesting physical prop-erties.However,owing to high reactivity of unpaired electrons,such open-shell organic diradicaloids are usually less stable than closed-shell systems,limiting their practical applications.In this study,we report P=O-attaching of diradical PHs as a new strategy to enhance their stability while maintaining diradi-cal properties.Three P=O-attached PHs containing the indeno[1,2-b]fluorene,fluoreno[3,2-b]fluorene and indeno[2,1-b]fluoreneπ-skeletons,respectively,were designed and synthesized.As theoretically and ex-perimentally proved,two of them have the relatively large diradical characters and open-shell singlet diradical nature.In comparison to their all-carbon analogues,the attached electron-withdrawing P=O groups endow them with much lower LUMO/HOMO energy levels but preserved magnetic activities and physical properties,such as thermally accessible triplet species and multi-redox ability.Moreover,the P=O groups effectively decrease their oxidation activities and thereby lead to their remarkably excellent ambient stabilities.Thus,this P=O-attaching strategy will be applicable to other diradical PH systems and may promote the generation of stable organic diradicaloids for radical chemistry and materials.

Thienothiophene-centered ladder-type π-systems that feature distinct quinoidal π-extension

Quinoidalπ-conjugated structures,a kind of fundamental subunits for organicπ-systems,may produce some intriguing optical,electronic and magnetic properties of polycyclic hydrocarbons(PHs).Herein,we report two thienothiophene-centered ladder-type polycyclic molecules(1 and 2),which possess one quinoidal thienothiophene moiety and two para-quinodimethane(p-QDM)subunits,respectively.As theoretically and experimentally studied,while 1 is a fully closed-shell molecule,2 owns an open-shell structure along with partial contribution of tetraradical state that is induced by the resonance of p-QDM.Moreover,although 2 has a largerπ-conjugated skeleton and open-shell electronic state,it exhibits larger bandgap and blue-shifted absorption.On the other hand,the reversible oxidation activity of 1 enables the preparation of its dication 1^(2+),and the studies on its single-crystal and aromatic structures demonstrate that its two positive charges are delocalized onto the oxygen atoms,thus achieving fullyπ-extended structure and near-infrared absorption.This study not only gains insight into quinoidalπ-subunits,but also provides an important basis for the development of antiaromatic and open-shellπ-electron materials.

A homopolymer based on double B←N bridged bipyridine as electron acceptor for all-polymer solar cells

Polymer electron acceptors for all-polymer solar cells （all-PSCs） are usually conjugated copolymers, which contain alternating electron-rich units and electron-deficient units. In this manuscript, we report a conjugated homopolymer （P-BNBP） based on an electron-deficient unit of double B,--N bridged bipyridine, which can be used as electron acceptor for all-polymer solar cells. P-BNBP shows low-lying LUMO energy level of -3.59eV, high absorption coefficient of 1.6 ×10^5Lmo1^-1 cm^-1 at 626nm and moderate electron mobility of 4.37 ×10^-6cm^2V^-1s^-1. AII-PSC devices exhibit power conversion efficiencies of 2.44%-3.04%. These results demonstrate that conjugated homopolymers are promising as electron acceptor materials for alI-PSCs.

A C_(54)B_(2) Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity

Doping heteroatoms into polycyclic aromatic hydrocarbons(PAHs)is an efficient strategy to achieve fascinating electronic structures and materials.However,nanoscale B-doped PAHs remain very challenging because of the intrinsic instability of the boron atom and the lack of suitable precursors.In this study,we report a C_(54)B_(2) polycyclicπ-system with one embedded 1,4-diboron-substituted benzene subunit,which was successfully synthesized from doubly B-doped heptazethrene.Thismolecule represents not only the largest B-doped PAH by far but also an unprecedented B-doped nanographene.The fully zigzag-armchair-edged structure creates a planar conformation,thus leading to its unique bilayer assembly behavior.More importantly,it possesses intriguing electronic structure and optoelectronic properties,such as very broad light absorption that covers 350–750 nm,sharp near-infrared fluorescence with a band width of only 26 nm,and reversible five-step redox capability,all of which are rarely observed for other B-doped PAHs.In addition,this molecule displays distinctive local aromaticity that cannot be reproduced via the reductive manipulation of an allcarbon congener.

Organoborane cyclophanes with flexible linkers: Dynamic coordination and photo-responsive fluorescence

Stimuli-responsive macrocycles are of importance for synthetic chemistry and smart materials. In this manuscript, we report two novel organoborane cyclophanes, which were successfully synthesized by ruthenium-catalyzed olefin metathesis. They are composed of one/two boron-doped helicene π-skeletons and flexible alkyl chain linkers, thus representing a new kind of non-conjugated organoborane macrocycles. Their cyclic structures and photophysical properties, as well as Lewis acidity were theoretically and experimentally investigated. Notably, two enantiomers in one single crystal are observed for one organoborane cyclophane, owning to the presence of helical π-framework in its cyclic structure. Moreover, their Lewis acid-base adducts may dissociate in the excited state and thus display intriguing photo-responsive fluorescence properties, which can be further modulated by temperature. This study thus provides a novel design strategy for non-conjugated organoborane macrocycles, which may promote the development of stimuli-responsive macrocyclic materials with fascinating properties.

Rodlike nanomaterials from organic diradicaloid with high photothermal conversion capability for tumor treatment

Organic diradicaloids with unique open-shell structures and properties have been widely used in organic electronics and spintronics.However,their advantageous optical properties have been explored less in the biomedical field.In this work,the photothermal conversion behaviors of a boron-containing organic diradicaloid(BOD)are reported.BOD can assemble with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol)to form rodlike nanoparticles(BOD NPs).These as-prepared BOD NPs exhibit high photothermal conversion capability and robust photothermal stability.Notably,they possess morphological superiority,which guarantees the effective photothermal therapy of tumors.This work thus demonstrates the promise of organic diradicaloids as efficient photothermal agents for biomedical applications.

Conjugated polymers containing B←N unit as electron acceptors for all-polymer solar cells

Polymer electron acceptors are the key materials in all-polymer solar cells(all-PSCs).In this review,we focused on introducing the principle of boron-nitrogen coordination bond(B←N),and summarizing our recent research on polymer electron acceptors containing B←N unit for efficient all-PSC devices.Two approaches have been reported to design polymer electron acceptors using B←N unit.One is to replace a C-C unit by a B←N unit in conjugated polymers to transform a polymer electron donor to a polymer electron acceptor.The other approach is to construct novel electron-deficient building block based on B←N unit for polymer electron acceptors.The polymer electron acceptors containing B←N unit showed tunable lowest unoccupied molecular orbital(LUMO) energy levels and exhibited excellent all-PSC device performance with power conversion efficiency of exceeding6%.These results indicate that organic boron chemistry is a new toolbox to develop functional polymer materials for optoelectronic device applications.

A new building block with intramolecular D-A character for conjugated polymers: ladder structure based on B←N unit

The general strategy to construct D-A type conjugated polymers is alternating copolymerization of electron-donating(D)monomer and electron-accepting(A)monomer.In this article,we report a new strategy to develop D-A type conjugated polymers,i.e.first fuse the D and A units into a polycyclic structure to produce a building block and then polymerize the building block with another unit.We develop a new building block with ladder structure based on B←N unit,B←N bridged dipyridylbenzene(BNDPB).In the skeleton of BNDPB,one diamine-substituted phenylene ring(D unit)and two B←N-linked pyridyl rings(A unit)are fused together to produce the polycyclic structure.Owning to the presence of intramolecular D-A character,the building block itself exhibits narrow bandgap of 1.74 eV.The conjugated polymers based on BNDPB show unique electronic structures,i.e.localized HOMOs and delocalized LUMOs,which are rarely observed for conventional D-A conjugated polymers.The polymers exhibit smaller bandgap than that of the building block BNDPB and display near-infrared(NIR)light absorption(λabs=ca.700 nm).This study thus provides not only a new strategy to design D-A conjugated polymers but also a new kind of building block with narrow bandgap.

B←N-containing azaacenes with propynyl groups on boron atoms

For organnoboron co mpounds,the substituents on boron atoms are very important because they not only impact on the molecular stability but also significantly modulate the electronic structu res and prope rties.In this manuscript,we synthesized two new B←N-co ntaining azaacenes with propynyl groups on boron atoms through one-step Grignard reaction.Replacing fluorine atoms by propynyl groups greatly impacts on the electronic energy levels,especially enhancing the HOMO levels,thus leading to the narrowed HOMO-LUMO bandgaps.These B←N-containing azaacenes exhibit the NIR light-absorption(λabs=706 nm for 2 a and 762 nm for 2 b)and fluorescence properties(λem=740 nm for 2 a and802 nm for 2 b),as well as multiple reversible redox behaviors,which are significantly different from the analogs with fluorine atoms.This study thus provides a functional substituent of boron atom,which may lead to new organoboron materials with fascinating properties.

Manipulating active layer morphology of molecular donor/polymer acceptor based organic solar cells through ternary blends

The development of molecular donor/polymer acceptor blend(MD/PA)-type organic solar cells(OSCs) lags far behind other type OSCs. It is due to the large-size phase separation morphology of MD/PAblend, which results from the high crystallinity of molecular donors. In this article, to suppress the crystallinity of molecular donors, we use ternary blends to develop OSCs based on one polymer acceptor(P-BNBP-f BT) and two molecular donors(DR3 TBDTT and BTR) with similar chemical structures.The ternary OSC exhibits a power conversion efficiency(PCE) of 4.85%, which is higher than those of the binary OSCs(PCE=3.60% or 3.86%). To our best knowledge, it is the first report of ternary MD/PA-type OSCs and this PCE is among the highest for MD/PA-type OSCs reported so far. Compared with the binary blends, the ternary blend exhibits decreased crystalline size and improved face-on orientation of the donors. As a result, the ternary blend exhibits improved and balanced charge mobilities, suppressed charge recombination and increased donor/acceptor interfacial areas, which leads to the higher shortcircuit current density. These results suggest that using ternary blend is an effective strategy to manipulate active layer morphology and enhance photovoltaic performance of MD/PA-type OSCs.