Donor-Linked Di(perylene bisimide)s: Arrays Exhibiting Fast Electron Transfer for Photosynthesis Mimics

The first example of donor-linked di­(perylene bisimide)­s is reported. UV–vis absorption spectra of these newly synthesized dyads showed intense absorption across the entire visible region, demonstrating their excellent light-harvesting activities. The severe fluorescence quenching event probed by steady-state fluorescence spectroscopy and the free-energy calculations suggested the possibility of electron transfer (ET) in these arrays upon photoexcitation. Further femtosecond transient absorption spectra clarified that the fluorescence quenching was due to fast intramolecular ET. The rate of the charge separation (CS) was found to be as high as 10¹² s^–1 in CH₂Cl₂. It was suggested that the large ET driving forces, strong donor–acceptor electronic coupling, and relatively small reorganization energy of diPBI accounted for the rapid ET process in a synergic manner. The fate of the generated radical ion pair depended on the solvent used. Rapid charge recombination to ground state occurred for the dyads in polar CH₂Cl₂ and for diPBI-TPA in nonpolar toluene. However, sufficient ³diPBI* population was attained via efficient spin–orbit coupled intersystem crossing from the charge-separated state for diPBI-PdTPP in toluene. These photophysical properties are interpreted as the cooperation between thermodynamic feasibility and kinetic manipulation

Self-Assembly of Perylenediimide Nanobelts and Their Size-Tunable Exciton Dynamic Properties

Upon the oxidation of perylenediimide dianion precursors, controlled release of neutral units paves the way for the solution-phase self-assembly of nanobelts via synergistic π–π stacking and hydrogen-bonding interactions. The obtained belt size has been regulated through adjusting the precursor supersaturation. This controlled synthesis also offers us an opportunity to explore size-tunable exciton dynamics features in the nanobelt, in which the competitive evolution to H-like exciton or excimer is found to be in strong relevance to the molecular packing and crystal size

Engineering of Interfacial Electron Transfer from Donor–Acceptor Type Organic Semiconductor to ZnO Nanorod for Visible-Light Detection

Interfacial electron transfer (IET) plays a key role in photoactive organic/inorganic hybrid nanomaterials and remains elusive with regard to interfacial energy level alignment. In this study, we prepared hybrid ZnO nanorods by grafting n-type perylene bisimide (PBI) derivatives bearing carboxylic acid groups at nitrogen positions. No evidence in terms of direct electron transfer from PBI to ZnO can be observed in PBI/ZnO hybrids. In sharp contrast, incorporation of electron-rich oligothiophene (<i>n</i>T, <i>n</i> = 1, 2) moieties into PBI core at bay positions resulted in a highly efficient cascade IET in <i>n</i>T-PBI/ZnO (<i>n</i> = 1, 2) hybrid nanorods, which was initiated by photoinduced electron transfer (PET) from <i>n</i>T (<i>n</i> = 1, 2) to PBI and then followed by charge shifting from PBI anion to ZnO across the interface. High performance UV–vis photodetectors based on <i>n</i>T-PBI/ZnO (<i>n</i> = 1, 2) hybrids have been fabricated and show responsivity of 21.2 and 12.4 A/W and an on/off ratio as high as 537 and 403, whereas that based on PBI/ZnO shows little visible-light response. Our results suggest that donor–acceptor type compounds can be used for constructing photoactive hybrid nanomaterials, in which efficient cascade IET modifies interfacial electronic structure and helps extend the spectral response range

Tunable Morphology of the Self-Assembled Organic Microcrystals for the Efficient Laser Optical Resonator by Molecular Modulation

Organic single-crystalline micro/nanostructures can effectively generate and carry photons due to their smooth morphologies, high photoluminescence quantum efficiency, and minimized defects density and therefore are potentially ideal building blocks for the optical circuits in the next generation of miniaturized optoelectronics. However, the tailor-made organic molecules can be generally obtained by organic synthesis, ensuring that the organic molecules aggregate in a specific form and generate micro/nanostructures with desirable morphology and therefore act as the efficient laser optical resonator remains a great challenge. Here, the molecular modulation of the morphology on the laser optical resonator properties has been investigated through the preparation of the elongated hexagonal microplates (PHMs) and the rectangular microplates (ORMs), respectively, from two model isomeric organic molecules of 1,4-bis­(4-methylstyryl)­benzene (<i>p</i>-MSB) and 1,4-bis­(2-methylstyryl)­benzene (<i>o</i>-MSB). Significantly, fluorescence resonance phenomenon was only observed in the individual ORM other than the PHM. It indicates that the rectangular resonators possess better light-confinement property over the elongated hexagonal resonators. More importantly, optically pumped lasing action was observed in the <i>o</i>-MSB rectangular morphology microplates resonator with a high <i>Q</i> ≈ 1500 above a threshold of ∼540 nJ/cm². The excellent optical properties of these microstructures are associated with the morphology, which can be precisely modulated by the organic molecular structure. These self-assembled organic microplates with different morphologies can contribute to the distinct functionality of photonics elements in the integrated optical circuits at micro/nanoscale

Photocurrent Enhancement of BODIPY-Based Solution-Processed Small-Molecule Solar Cells by Dimerization via the Meso Position

Three 4,4-difluoro-4-bora-3a,4a-diaza-<i>s</i>-indancene (BODIPY)-based small molecule donors <b>H-T-BO</b>, <b>Br-T-BO</b>, and <b>DIMER</b> were synthesized and fully characterized. Although modification at the meso position has a subtle influence on the light-harvesting ability, energy levels, and phase sizes, it has a striking effect on the packing behavior in solid film as two-dimension grazing incidence X-ray diffraction (2D GIXRD) and X-ray diffraction (XRD) confirm. <b>Br-T-BO</b> exhibits better packing ordering than <b>H-T-BO</b> in pristine film, which is beneficial from reinforced intermolecular interaction from halogen atoms. However, when [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) is blended, no diffraction patterns corresponding to the monomeric donor can be seen from the XRD data and both <b>H-T-BO</b>- and <b>Br-T-BO</b>-based blend films give a slightly blue-shifting absorption peak with respect to their neat ones, both of which imply destruction of the crystalline structure. As for <b>DIMER</b>, the enhancement of the intermolecular interaction arises not only from the expansion of the backbone but the “steric pairing effect” brought on by its twisted structure. When blended with PC₇₁BM, the diffraction patterns of <b>DIMER</b> are, however, kept well and the absorption peak position remains unchanged, which indicates the ordered packing of <b>DIMER</b> is held well in blend film. In coincidence with the fact that packing ordering improves from <b>H-T-BO</b> to <b>Br-T-BO</b> and <b>DIMER</b> in pristine films and the ordered packing of <b>DIMER</b> even in blend film, <b>DIMER</b>-based devices show the highest and most balanced hole/electron mobility of 1.16 × 10^–3/0.90 × 10^–3 cm² V^–1 s^–1with respect to <b>Br-T-BO</b> (4.71 × 10^–4/2.09 × 10^–4 cm² V^–1 s^–1) and <b>H-T-BO</b> (4.27 × 10^–5/1.00 × 10^–5 cm² V^–1 s^–1) based ones. The short-circuit current density of the three molecule-based cells follows the same trend from <b>H-T-BO</b> (6.80) to <b>Br-T-BO</b> (7.62) and then to <b>DIMER</b> (11.28 mA cm^–2). Finally, the <b>H-T-BO</b>-, <b>Br-T-BO</b>-, and <b>DIMER</b>-based optimal device exhibits a power conversion efficiency of 1.56%, 1.96%, and 3.13%, respectively

Exceptional Intersystem Crossing in Di(perylene bisimide)s: A Structural Platform toward Photosensitizers for Singlet Oxygen Generation

Photosensitized reactions of molecular oxygen have found far-reaching applications in various fields, and the development of new photosensitizer compounds is of crucial importance. We here describe a new class of triply linked bay-fused diperylene bisimides (DiPBIs) which exhibited several unique features, rendering them a new structural platform for the development of highly efficient and photostable photosensitizers. (i) The extended π-conjugation shifts its absorption into the body’s therapeutic window. (ii) The nonplanarity of the distorted cores enhances the spin−orbit coupled intersystem crossing. (iii) The long-lasting high-energy T₁ state facilitates singlet oxygen generation via energy-transfer reaction between T₁ and ground-state oxygen

Highly Efficient Room-Temperature Phosphorescence from Halogen-Bonding-Assisted Doped Organic Crystals

The development of metal-free organic room temperature phosphorescence (RTP) materials has attracted increasing attention because of their applications in sensors, biolabeling (imaging) agents and anticounterfeiting technology, but remains extremely challenging owing to the restricted spin-flip intersystem crossing (ISC) followed by low-yield phosphorescence that cannot compete with nonradiative relaxation processes. Here, we report a facile strategy to realize highly efficient RTP by doping iodo difluoroboron dibenzoylmethane (I-BF₂dbm-R) derivatives into a rigid crystalline 4-iodobenzonitrile (Iph-CN) matrix. We found that halogen bonding between cyano group of Iph-CN matrix and iodine atom of I-BF₂dbm-R dopant is formed in doped crystals, i.e., Iph-CN···I-BF₂dbm-R, which not only suppresses nonradiative relaxation of triplets but also promotes the spin–orbit coupling (SOC). As a result, the doped crystals show intense RTP with an efficiency up to 62.3%. By varying the substituent group R in I-BF₂dbm-R from electron donating −OCH₃ to electron accepting −F, −CN groups, the ratio between phosphorescence and fluorescence intensities has been systematically increased from 3.8, 15, to 50

Exciton-Polaritons with Size-Tunable Coupling Strengths in Self-Assembled Organic Microresonators

Self-assembled nano/microcrystals of organic semiconductors with regular faces can serve as optical microresonators, which hold a promise for studying the light confinement and the light-matter interaction. Here, single crystalline microribbons of 1,4-bis­(2-(4-(<i>N</i>,<i>N</i>-di­(<i>p</i>-tolyl)­amino)­phenyl)-vinylbenzene (DPAVB) are synthesized with well-controlled sizes by a facile solution-exchange method. We find that individual microribbon can work as Fabry-Pérot (FP) resonator along its width (<i>w</i>), in which strong coupling of optical modes with excitons results in the formation of exciton polaritons (EPs). The dispersion relation of <i>E</i> ∼ <i>k</i>_<i>z</i> of EPs is constructed by extracting the energies (<i>E</i>) of FP resonances at integer multiples of π/<i>w</i> in the wavevector (<i>k</i>_<i>z</i>) space. By simulating the significantly curved dispersion of EPs with a two coupled harmonic oscillator model, a coupling strength between 0.48 and 1.09 eV are obtained. Two coupling regimes are classified: in regime I, the coupling strength is constant at 0.48 eV for microribbons with the cavity length of <i>w</i> ≥ 2.00 μm; in regime II, the coupling strength increases dramatically from 0.48 to about 1 eV with decreasing the resonator length from <i>w</i> = 2.00 to 0.83 μm. More significantly, our results suggest that the exciton-photon coupling strength could be modulated by varying the size of microribbon cavities, providing an effective method for engineering the light–matter interaction in organic single crystalline microstructures

Organic Phosphorescence Nanowire Lasers

Organic solid-state lasers (OSSLs) based on singlet fluorescence have merited intensive study as an important class of light sources. Although the use of triplet phosphors has led to 100% internal quantum efficiency in organic light-emitting diodes (OLEDs), stumbling blocks in triplet lasing include generally forbidden intersystem crossing (ISC) and a low quantum yield of phosphorescence (Φ_P). Here, we reported the first triplet-phosphorescence OSSL from a nanowire microcavity of a sulfide-substituted difluoroboron compound. As compared with the unsubstituted parent compound, the lone pair of electrons of sulfur substitution plus the intramolecular charge transfer interaction introduced by the nitro moiety lead to an highly efficient T₁ (π,π*) ← S₁ (n,π*) ISC (Φ_ISC = 100%) and a moderate Φ_P (10%). This, plus the optical feedback provided by nanowire Fabry–Perot microcavity, enables triplet-phosphorescence OSSL emission at 650 nm under pulsed excitation. Our results open the door for a whole new class of laser materials based on previously untapped triplet phosphors

Highly Efficient Room-Temperature Phosphorescence from Halogen-Bonding-Assisted Doped Organic Crystals

The development of metal-free organic room temperature phosphorescence (RTP) materials has attracted increasing attention because of their applications in sensors, biolabeling (imaging) agents and anticounterfeiting technology, but remains extremely challenging owing to the restricted spin-flip intersystem crossing (ISC) followed by low-yield phosphorescence that cannot compete with nonradiative relaxation processes. Here, we report a facile strategy to realize highly efficient RTP by doping iodo difluoroboron dibenzoylmethane (I-BF₂dbm-R) derivatives into a rigid crystalline 4-iodobenzonitrile (Iph-CN) matrix. We found that halogen bonding between cyano group of Iph-CN matrix and iodine atom of I-BF₂dbm-R dopant is formed in doped crystals, i.e., Iph-CN···I-BF₂dbm-R, which not only suppresses nonradiative relaxation of triplets but also promotes the spin–orbit coupling (SOC). As a result, the doped crystals show intense RTP with an efficiency up to 62.3%. By varying the substituent group R in I-BF₂dbm-R from electron donating −OCH₃ to electron accepting −F, −CN groups, the ratio between phosphorescence and fluorescence intensities has been systematically increased from 3.8, 15, to 50