The development of solution-processable fluorescent small molecules with highly efficient deep-blue electroluminescence is of growing interest for organic light-emitting diode (OLED) applications. However, high-performance deep-blue fluorescent emitters with external quantum efficiencies (EQEs) over 5% are still scarce in OLEDs. Herein, a novel highly soluble oligo­(p-phenyleneethynylene)-based small molecule, 1,4-bis­((2-cyanophenyl)­ethynyl)-2,5-bis­(2-ethylhexyloxy)­benzene (2EHO–CNPE), is designed, synthesized, and fully characterized as a wide band gap (2.98 eV) and highly fluorescent (ΦPL = 0.90 (solution) and 0.51 (solid-state)) deep-blue emitter. The new molecule is functionalized with cyano (-CN)/2-ethylhexyloxy (-OCH2CH­(C2H5)­C4H9) electron-withdrawing/-donating substituents, and ethynylene is used as a π-spacer to form an acceptor (A)−π–donor (D)−π–acceptor (A) molecular architecture with hybridized local and charge transfer (HLCT) excited states. Physicochemical and optoelectronic characterizations of the new emitter were performed in detail, and the single-crystal structure was determined. The new molecule adopts a nearly coplanar π-conjugated framework packed via intermolecular “C–H···π” and “C–H···N” hydrogen bonding interactions without any π–π stacking. The OLED device based on 2EHO–CNPE shows an EQEmax of 7.06% (EQE = 6.30% at 200 cd/m2) and a maximum current efficiency (CEmax) of 5.91 cd/A (CE = 5.34 cd/A at 200 cd/m2) with a deep-blue emission at CIE of (0.15, 0.09). The electroluminescence performances achieved here are among the highest reported to date for a solution-processed deep-blue fluorescent small molecule, and, to the best of our knowledge, it is the first time that a deep-blue OLED is reported based on the oligo­(p-phenyleneethynylene) π-framework. TDDFT calculations point to facile reverse intersystem crossing (RISC) processes in 2EHO–CNPE from high-lying triplet states to the first singlet excited state (T2/T3 → S1) (hot-exciton channels) that enable a high radiative exciton yield (ηr ∼ 69%) breaking the theoretical limit of 25% in conventional fluorescent OLEDs. These results demonstrate that properly designed fluorescent oligo­(p-phenyleneethynylenes) can be a key player in high-performance deep-blue OLEDs.

A novel oligo(p-phenyleneethynylene)-based hot-exciton molecule with hybridized local and charge transfer (HLCT) excited states was developed to yield high radiative exciton yields in OLEDs.

Molecular engineering via functionalization has been a great tool to tune noncovalent intermolecular interactions. Herein, we demonstrate three-dimensional highly crystalline nanostructured D(C7CO)-BTBT films via carbonyl-functionalization of a fused thienoacene π-system, and strong Raman signal enhancements in Surface-Enhanced Raman Spectroscopy (SERS) are realized. The small molecule could be prepared on the gram scale with a facile synthesis-purification. In the engineered films, polar functionalization induces favorable out-of-plane crystal growth via zigzag motif of dipolar C = O···C = O interactions and hydrogen bonds, and strengthens π-interactions. A unique two-stage film growth behavior is identified with an edge-on-to-face-on molecular orientation transition driven by hydrophobicity. The analysis of the electronic structures and the ratio of the anti-Stokes/Stokes SERS signals suggests that the π-extended/stabilized LUMOs with varied crystalline face-on orientations provide the key properties in the chemical enhancement mechanism. A molecule-specific Raman signal enhancement is also demonstrated on a high-LUMO organic platform. Our results demonstrate a promising guidance towards realizing low-cost SERS-active semiconducting materials, increasing structural versatility of organic-SERS platforms, and advancing molecule-specific sensing via molecular engineering.

Polycyclic π-conjugated hydrocarbons (PCHs), either unfunctionalized or structurally modified derivatives, have attracted tremendous interest in the past few decades as high-performance semiconductors for use in new generations of organic (opto)electronic...

The realization of π-deficient acceptors and their donor− acceptor copolymers has become a key research focus for the realization of versatile organic optoelectronic materials and devices. Herein, we demonstrate the theoretical design, synthesis, and physicochemical/ optoelectronic characterization of two meso-π-extended/deficient BOD-IPY building blocks (2OD−T2BDY and 2OD−TTzBDY) and a library of donor−acceptor copolymers with low band gap (E g = 1.30−1.35 eV) based on these building blocks. These building blocks, to the best of our knowledge, are the first examples of BODIPYs with meso-π-extension. A library of BODIPY building blocks with varied meso units/substituents is studied to reveal the meso effects on the semiconducting BODIPY's optoelectronic properties. The building blocks showed favorable πacceptor electronic/structural properties with meso-π-delocalized and stabilized LUMOs (ca. −3.6 eV) and large ground-state dipole moments of 4.9−5.5 D. Consistent with the theoretical/experimental π-electronic structures, all copolymers functioned as p-type semiconductors in field-effect transistors and as donor materials in the bulk heterojunction organic photovoltaics. Power conversion efficiencies of up to 4.4% with a short-circuit current of 12.07 mA cm −2 were achieved. This study demonstrates a unique meso-πextension strategy to realize BODIPYs with favorable π-acceptor properties, and our findings could open up future materials design avenues in various organic optoelectronic applications.