A Pentacoordinate Boron-Containing π‑Electron System with Cl–B–Cl Three-Center Four-Electron Bonds

Tricoordinate boron-containing π-electron systems are an attractive class of compounds with intense fluorescence and strong electron-accepting properties. However, the impact of pentacoordination of the boron atoms on their properties has not been determined. We now disclose a <i>B</i>,<i>B</i>′-bis­(1,8-dichloro-9-anthryl)-substituted 9,10-dihydro-9,10-diboraanthracene as a new pentacoordinate organoboron compound. In this skeleton, with the aid of the orthogonal arrangement of the anthryl substituent, the B and Cl atoms can form a three-center four-electron (3c–4e) Cl–B–Cl bond. The pentacoordination of the boron atom significantly perturbs the electronic structure and thereby the photophysical and electrochemical properties

Fine-Tuning LUMO Energy Levels of Conjugated Polymers Containing a B←N Unit

The LUMO and HOMO energy levels (<i>E</i>_LUMO/<i>E</i>_HOMO) are key parameters for conjugated polymers, which can greatly affect their applications in organic opto-electronic devices. In this manuscript, with donor–acceptor (D–A) type conjugated polymers based on double B←N bridged bipyridine (BNBP) unit, we report fine-tuning of <i>E</i>_LUMO of conjugated polymers in a wide range via substitutions on both D unit and A unit. We synthesize eight D–A type conjugated polymers with alternating electron-deficient BNBP unit and electron-rich bithiophene (BT) unit in the main chain. By changing the substitutes on BNBP or BT, the <i>E</i>_LUMO of these polymers can be finely tuned in a wide range from −3.3 eV to −3.7 eV. We comprehensively investigate the electronic structures, photophysical properties, charge-transporting properties and polymer solar cell (PSC) device applications of these polymers. In PSC devices, these BNBP-based polymers can be used either as electron donors (with high-lying <i>E</i>_LUMO/<i>E</i>_HOMO) or as electron acceptors (with low-lying <i>E</i>_LUMO/<i>E</i>_HOMO). The PSC device with the BNBP-based polymer donor exhibits a PCE of 2.92% and the PSC device with the BNBP-based polymer acceptor exhibits a PCE of 5.16%. These results indicate a new approach to modulate the LUMO energy levels of D–A type conjugated polymers by modifications on both D unit and A unit

Multi-Stimuli-Responsive Fluorescence Switching of a Donor−Acceptor π-Conjugated Compound

An electron donor−acceptor structured π-conjugated organic compound <b>1</b> composed of trifluoromethyl-biphenyl and cyano-stilbene-amine was designed and exhibited multi-stimuli-responsive fluorescence switching behaviors. The synthesized solid exhibited piezochromism in that grinding and heating could change the emission colors between orange-red and yellow. The amorphous <b>1</b> also showed interesting vapochromic behavior in that organic vapor could convert the yellow color into orange. The solution of <b>1</b> exhibited nearly no fluorescence at room temperature and intensive yellowish green emission at 77 K, while adding CF₃COOH (TFA) resulted in green emissive state at room temperature and blue fluorescent state at 77 K

Multi-Stimuli-Responsive Fluorescence Switching of a Donor−Acceptor π-Conjugated Compound

An electron donor−acceptor structured π-conjugated organic compound <b>1</b> composed of trifluoromethyl-biphenyl and cyano-stilbene-amine was designed and exhibited multi-stimuli-responsive fluorescence switching behaviors. The synthesized solid exhibited piezochromism in that grinding and heating could change the emission colors between orange-red and yellow. The amorphous <b>1</b> also showed interesting vapochromic behavior in that organic vapor could convert the yellow color into orange. The solution of <b>1</b> exhibited nearly no fluorescence at room temperature and intensive yellowish green emission at 77 K, while adding CF₃COOH (TFA) resulted in green emissive state at room temperature and blue fluorescent state at 77 K

Polymer Electron Acceptors with Conjugated Side Chains for Improved Photovoltaic Performance

The development of polymer electron acceptors lags far behind that of polymer electron donors. A general approach to improve photovoltaic performance of polymer electron donors is to incorporate conjugated side chains to the electron-rich unit. In this article, we introduce the “conjugated side chain” strategy to molecular design of polymer electron acceptors by incorporating conjugated side chains to the electron-deficient unit. The polymer backbones consist of alternating electron-deficient double B←N bridged bipyridine (BNBP) unit and electron-rich thiophene or selenophene unit. Polymer electron acceptors are developed by incorporating conjugated alkoxyphenyl side chains to the BNBP unit. Compared with conventional alkyl side chains, the conjugated alkoxyphenyl side chains endow the polymer electron acceptors with low-lying LUMO energy levels, enhanced π–π stacking, and high electron mobilities, which are very desirable for electron acceptors. The resulting all-PSCs exhibit an enhanced power conversion efficiency (PCE) of 4.46% with a small photon energy loss (<i>E</i>_loss) of 0.51 eV or a PCE of 3.77% with an extremely small <i>E</i>_loss of 0.47 eV. This <i>E</i>_loss is among the smallest values reported for organic solar cells. These results demonstrate that the “conjugated side chain” strategy can be used not only for high-efficiency polymer electron donors but also for high-performance polymer electron acceptors

Sequential Electrophilic and Photochemical Cyclizations from Bis(bithienyl)acetylene to a Tetrathienonaphthalene Core

Photoirradiation of bis(bithienyl)acetylenes in the presence of iodine undergoes sequential electrophilic and photochemical cyclizations to produce tetrathienonaphthalenes (TTN) in one pot. The TTN framework is readily transformed into cruciform π-extended derivatives, which form ordered nano/microstructures

Sequential Electrophilic and Photochemical Cyclizations from Bis(bithienyl)acetylene to a Tetrathienonaphthalene Core

Photoirradiation of bis(bithienyl)acetylenes in the presence of iodine undergoes sequential electrophilic and photochemical cyclizations to produce tetrathienonaphthalenes (TTN) in one pot. The TTN framework is readily transformed into cruciform π-extended derivatives, which form ordered nano/microstructures

Sequential Electrophilic and Photochemical Cyclizations from Bis(bithienyl)acetylene to a Tetrathienonaphthalene Core

Photoirradiation of bis(bithienyl)acetylenes in the presence of iodine undergoes sequential electrophilic and photochemical cyclizations to produce tetrathienonaphthalenes (TTN) in one pot. The TTN framework is readily transformed into cruciform π-extended derivatives, which form ordered nano/microstructures

Sequential Electrophilic and Photochemical Cyclizations from Bis(bithienyl)acetylene to a Tetrathienonaphthalene Core

Photoirradiation of bis(bithienyl)acetylenes in the presence of iodine undergoes sequential electrophilic and photochemical cyclizations to produce tetrathienonaphthalenes (TTN) in one pot. The TTN framework is readily transformed into cruciform π-extended derivatives, which form ordered nano/microstructures