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(Poly)terephthalates with Efficient Blue Emission in the Solid State
摘要： We prepared dimethyl and diaryl 2,5-dialkoxyterephthalates from dimethyl 2,5-dihydroxyterephthalate in good-to-high yields via alkylation or a sequence of alkylation, hydrolysis, chlorination, and condensation. The absorption spectra of the dialkoxyterephthalates contain a small band at 332–355 nm, which could be assigned to intramolecular charge-transfer transition from the alkoxy to alkoxycarbonyl groups on the basis of theoretical calculations using density functional theory. The dialkoxyterephthalates exhibited blue fluorescence with moderate-to-excellent quantum yields not only in solution but also in the solid state, such as a poly(methyl methacrylate) (PMMA) film and a powder. The solid-state quantum yields of the diisopropoxy-substituted terephthalates were similar or considerably higher than those of the dimethoxy-substituted counterparts. Copolymerization of 2,5-diisopropoxyterephthaloyl chloride and 1,4-butanediol with or without terephthaloyl chloride gave brilliantly blue fluorescent polymers, whose quantum yields were 0.72 and 0.71 in toluene and 0.46 and 0.40 in the neat film, respectively. Furthermore, white emission was achieved when a fluorescent yellow 2,5-diaminoterephthalate was doped into the thin film of the blue fluorescent polymer at 0.4 wt %.
关键词： materials science,arenes,donor-acceptor systems,conjugation,fluorescence
更新于2025-09-23 15:23:52
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Highly Polarized Coumarin Derivatives Revisited: Solvent-controlled Competition Between Proton Coupled Electron Transfer and Twisted Intramolecular Electron Transfer
摘要： Linking a polarized coumarin unit with an aromatic substituent via an amide bridge results in weak electronic coupling affecting the intramolecular electron transfer (ET) process. As a result of this, interesting solvent-dependent photophysical properties can be observed. In polar solvents, electron transfer in coumarin derivatives of this type induces a mutual twist of electron-donating and electron-accepting molecular units (TICT process) that opens radiationless decay processes (internal conversion). In the dyad with the strongest intramolecular hydrogen bond, the planar form is stabilized so twisting can only occur in highly polar solvents, whereas fast proton coupled electron transfer (PCET process) occurs in non-polar n-alkanes. The kPCET rate constant decreases linearly with the fluorescence maximum energy in different solvents. This observation is explained in terms of competition between electron and proton transfer from a highly polarized (~15 D) and fluorescent locally-excited (1LE) state to a much less polarized (~4 D) charge-transfer (1CT) state, a unique occurrence. Photophysical measurements performed for a family of related coumarin dyads together with results of quantum-chemical computations give insight into the mechanism of the ET process which is followed by either a TICT or PCET process. Our results reveal that dielectric solvation of the excited state slows down the PCET process, even in non-polar solvents.
关键词： coumarins,donor-acceptor systems,absorption,fluorescence,chromophores
更新于2025-09-23 15:21:01
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Synthesis and Photovoltaic Properties of Boron ?2a??Ketoiminate Dyes Forming A Linear Donora????a??Acceptor Structure
摘要： Organoboron complexes are of interest as chromophores for dye sensitizers owing to their light-harvesting and carrier-transporting properties. In this study, compounds containing boron β-ketoiminate (BKI) as a chromophore were synthesized and used as dye sensitizers in dye-sensitized solar cells. The new dyes were orange or red crystals and showed maximum absorptions in the 410–450 nm wavelength region on titanium dioxide substrates. These electrodes exhibited maximum efficiencies of over 80% in incident photon-to-current conversion efficiency spectra, suggesting that the continuous process of light absorption–excitation–electron injection was effectively performed. Open-circuit photovoltages were relatively high owing to the large dipole moments of the BKI dyes with a linear molecular structure. Thus, a maximum power conversion efficiency of 5.3% was successfully observed. Comparison of BKI dyes with boron β-diketonate dyes revealed certain differences in solution stability, spectral properties, and photovoltaic characteristics.
关键词： chelates,boron,donor-acceptor systems,dyes/pigments,energy conversion
更新于2025-09-23 15:21:01
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Molecular Engineering of Simple Metal‐Free Organic Dyes Derived from Triphenylamine for Dye‐Sensitized Solar Cell Applications
摘要： Two new metal-free organic sensitizers, L156 and L224, were designed, synthesized, and characterized for application in dye-sensitized solar cells (DSCs). The structures of the dyes contain a triphenylamine (TPA) segment and 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid as electron-rich and -deficient moieties, respectively. Two different π bridges, thiophene and 4,8-bis(4-hexylphenyl)benzo[1,2-b:4,5-b’]dithiophene, were used for L156 and L224, respectively. The influence of iodide/triiodide, [Co(bpy)3]2+/3+ (bpy = 2,2’-bipyridine), and [Cu(tmby)2]2+/+ (tmby = 4,4’,6,6’-tetramethyl-2,2’-bipyridine) complexes as redox electrolytes and 18 NR-T and 30 NR-D transparent TiO2 films on the DSC device performance was investigated. The L156-based DSC with [Cu(tmby)2]2+/+ complexes as the redox electrolyte resulted in the best performance of 9.26 % and a remarkably high open-circuit voltage value of 1.1 V (1.096 V), with a short-circuit current of 12.2 mA cm?2 and a fill factor of 0.692, by using 30 NR-D TiO2 films. An efficiency of up to 21.9 % was achieved under a 1000 lx indoor light source, which proved that dye L156 was also an excellent candidate for indoor applications. The maximal monochromatic incident-photon-to-current conversion efficiency of L156–30 NR-D reached up to 70 %.
关键词： electrochemistry,donor–acceptor systems,dyes/pigments,sensitizers,solar cells
更新于2025-09-11 14:15:04
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Dipolar and Quadrupolar Luminophores Based on 1,8‐Dimethylcarbazole?Triazine Conjugates for High‐Efficiency Blue Thermally Activated Delayed Fluorescence OLEDs
摘要： Highly efficient blue thermally activated delayed fluorescence emitters combining 1,8-dimethylcarbazoles as a donor (D) unit with a triazine acceptor (A) core are designed and synthesized. A D-A-D-type emitter exhibits superior photo- and electroluminescence (EL) properties compared to a D-A-type counterpart and displays a brilliant blue EL emission with a maximum external EL quantum efficiency as high as 21.2 %.
关键词： organic light-emitting diodes,optoelectronics,donor-acceptor systems,electroluminescence,delayed fluorescence
更新于2025-09-11 14:15:04
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Stereospecific [2+2]-cross-photocycloaddition in a supramolecular donor–acceptor complex
摘要： A bis(propylammonium) derivative of (E)-4-(4-mercaptostyryl)pyridine, which was synthesized for the first time, forms a highly stable bimolecular complex with a bis(18-crown-6 ether) derivative of (E)-stilbene in solution owing to ditopic coordination via hydrogen bonds. The complex formation results in much faster deactivation of the excited states of both compounds, which is explained by photoinduced electron transfer from the stilbene derivative to the styrylpyridinium dye. Despite this, the complexed olefins undergo [2+2]-cross-photocycloaddition upon selective excitation of the dye to afford solely the syn-cycloadduct. The retro-photocycloaddition occurs readily upon UV irradiation of the cycloadduct and leads to the initial bimolecular complex.
关键词： Photoinduced electron transfer,Donor–acceptor systems,Cross-photocycloaddition,Self-assembly
更新于2025-09-10 09:29:36