Dipolar metal‐free sensitizers (D‐π‐A; D=donor, π=conjugated bridge, A=acceptor) consisting of a dithiafulvalene (DTF) unit as the electron donor, a benzene, thiophene, or fluorene moiety as the conjugated spacer, and 2‐cyanoacrylic acid as the electron acceptor have been synthesized. Dimeric congeners of these dyes, (D‐π‐A)2, were also synthesized through iodine‐induced dimerization of an appropriate DTF‐containing segment. Dye‐sensitized solar cells (DSSCs) with the new dyes as the sensitizers have cell efficiencies that range from 2.11 to 5.24 %. In addition to better light harvesting, more effective suppression of the dark current than the D‐π‐A dyes is possible with the (D‐π‐A)2 dyes. 相似文献
In the current study, new carbazole‐based formazan dyes, D‐A and D‐π‐A, were synthesized, and their spectroscopic properties were studied for the first time. For this aim, carbazole aldehyde compounds were modified by the derivatization of carbazole, a natural electron‐donor compound, from 3‐ and 9‐position. Then, hydrazone derivatives were synthesized from these aldehyde derivatives. Finally, D‐A ( 5A–C ) and D‐π‐A ( 6A–C ) carbazole–formazan dyes were obtained by the interaction of the hydrazone compounds with p‐substituted aniline. After characterization of the structures of these compounds, photophysical properties of the carbazole–formazans were studied in the different polarity media (i.e., acetonitrile, toluene, and chloroform) in order to detect the solvent effects. Because of the π‐conjugated bridge and the electron acceptor nitro group at the para position, D‐π‐A structured carbazole–formazan dye 6C showed the highest Stokes shift of 155 nm. 相似文献
Four new type II organic dyes with D‐π‐A structure (donor‐π‐conjugated‐acceptor) and two typical type II sensitizers based on catechol as reference dyes are synthesized and applied in dye sensitized solar cells (DSCs). The four dyes can be adsorbed on TiO2 through hydroxyl group directly. Electron injection can occur not only through the anchoring group (hydroxyl group) but also through the electron‐withdrawing group (? CN) located close to the semiconductor surface. Experimental results show that the type II sensitizers with a D‐π‐A system obviously outperform the typical type II sensitizers providing much higher conversion efficiency due to the strong electronic push‐pull effect. Among these dyes, LS223 gives the best solar energy conversion efficiency of 3.6%, with Jsc=7.3 mA·cm?2, Voc=0.69 V, FF=0.71, the maximum IPCE value reaches 74.9%. 相似文献
Herein, two new quadrupolar acceptor‐π‐donor‐π‐acceptor (A‐π‐D‐π‐A) chromophores have been prepared featuring a strongly electron‐donating diborene core and strongly electron‐accepting dimesitylboryl (BMes2) and bis(2,4,6‐tris(trifluoromethyl)phenyl)boryl (BFMes2) end groups. Analysis of the compounds by NMR spectroscopy, X‐ray crystallography, cyclic voltammetry, and UV/Vis‐NIR absorption and emission spectroscopy indicated that the compounds have extended conjugated π‐systems spanning their B4C8 cores. The combination of exceptionally potent π‐donor (diborene) and π‐acceptor (diarylboryl) groups, both based on trigonal boron, leads to very small HOMO–LUMO gaps, resulting in strong absorption in the near‐IR region with maxima in THF at 840 and 1092 nm and very high extinction coefficients of ca. 120 000 m ?1 cm?1. Both molecules also display weak near‐IR fluorescence with small Stokes shifts. 相似文献
A series of N‐methyl‐3,4‐fulleropyrrolidine (NMFP) derivatives were designed by selecting different π‐conjugated linkers and electron‐donating groups as D‐π‐A and D‐A systems. The optimised structures and photo‐physical properties of NMFP and its derivatives have been determined using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods with the B3LYP functional and the 6‐31G basis set. According to the computation analysis, both the π‐conjugated linkers and the electron‐donating groups can influence the electronic and photo‐physical properties of the NMFP derivatives. Our calculated results demonstrated that the electron‐donating groups, with significant electron‐donating ability, had the tendency to increase the highest occupied molecular orbital (HOMO) energy. The π‐conjugated linkers with lower resonance energy decreased the lowest occupied molecular orbital (LUMO) energy and caused a significant decrease in the energy gap (Eg) between the EHOMO and ELUMO. A Natural Bond Orbital (NBO) analysis examines the effect of the electron‐donating group, π conjugated linker, and electron‐withdrawing group for these NMFP derivatives. For the NMFP derivatives, a projected density of state (PDOS) analysis demonstrated that the electron density of HOMO and LUMO are concentrated on the electron‐donating group and the π‐conjugated linker, respectively. A TD‐DFT/B3LYP calculation was performed to calculate the electronic absorption spectra of these NMFP derivatives. Both the electron‐donating group and the π‐conjugated linker contribute to the major absorption peaks, which are assigned as HOMO to LUMO transitions and are red‐shifted relative to those of non‐substituted NMFP. 相似文献
Fluorescent materials exhibiting two‐photon induction (TPI) are used for nonlinear optics, bioimaging, and phototherapy. Polymerizations of molecular chromophores to form π‐conjugated structures were hindered by the lack of long‐range ordering in the structure and strong π–π stacking between the chromophores. Reported here is the rational design of a benzothiadiazole‐based covalent organic framework (COF) for promoting TPI and obtaining efficient two‐photon induced fluorescence emissions. Characterization and spectroscopic data revealed that the enhancement in TPI performance is attributed to the donor‐π‐acceptor‐π‐donor configuration and regular intervals of the chromophores, the large π‐conjugation domain, and the long‐range order of COF crystals. The crystalline structure of TPI‐COF attenuates the π–π stacking interactions between the layers, and overcomes aggregation‐caused emission quenching of the chromophores for improving near‐infrared two‐photon induced fluorescence imaging. 相似文献
Due to the ease of tuning its redox potential, the cobalt‐based redox couple has been extensively applied for highly efficient dye‐sensitized solar cells (DSSCs) with extraordinarily high photovoltages. However, a cobalt electrolyte needs particular structural changes in the organic dye components to obtain such high photovoltages. To achieve high device performance, specific requirements in the molecular tailoring of organic sensitizers still need to be met. Besides the need for large electron donors, studies of the auxiliary acceptor segment of donor–acceptor–π‐acceptor (D‐A‐π‐A) organic sensitizers are still rare in molecular optimization in the context of cobalt electrolytes. In this work, two novel organic D‐A‐π‐A‐type sensitizers ( IQ13 and IQ17 ) have been developed and exploited in cobalt‐ and iodine‐based redox electrolyte DSSCs, specifically to provide insight into the effect of π‐bridge modification in different electrolytes. The investigation has been focused on the additional electron‐withdrawing acceptor capability with grafted long alkoxy chains. Optoelectronic transient measurements have indicated that IQ17 containing a pyrido[3,4‐b]pyrazine moiety bearing long alkoxyphenyl chains is more suitable for application in cobalt‐based DSSCs. 相似文献
The donor‐π‐conjugated‐acceptor (D‐π‐A) structure is an important design for the luminescent materials because of its diversity in the selections of donor, π‐bridge and acceptor groups. Herein, we demonstrate two examples of D‐π‐A structures capable to finely modulate the excited state properties and arrangement of energy levels, TPA‐AN‐BP and CZP‐AN‐BP , which possess the same acceptor and π‐bridge but different donor. The investigation of their photophysical properties and DFT calculation revealed that the D‐π‐A structure with proper donor, π‐bridge and acceptor can result in separation of frontier molecular orbitals on the corresponding donor and acceptor with an obvious overlap on the π‐bridge, resulting in a hybridized local and charge‐transfer (HLCT ) excited state with high photoluminescent (PL ) efficiencies. Meanwhile, their singlet and triplet states are arranged on corresponding moieties with large energy gap between T2 and T1 , and a small energy gap between S1 and T2 , which favor the reverse intersystem crossing (RISC ) from high‐lying triplet levels to singlet levels. As a result, the sky‐blue emission non‐doped OLED based on the TPA‐AN‐BP reached maximum external quantum efficiency (EQE ) of 4.39% and a high exciton utilization efficiency (EUE ) of 77%. This study demonstrates a new strategy to construct highly efficient OLED materials. 相似文献
Three new donor–π–donor (D‐π‐D) tetrathienoacene (thieno[2′,3′:4,5]thieno[3,2‐b]thieno[2,3‐d]thiophene (TTA))‐cored chromophores, end‐functionalized with electron‐donating triphenylamine (TPA) groups, were developed and characterized for their two‐photon‐related properties by using both nano‐ and femtosecond laser pulses as the probing tools. TTA‐based chromophores exhibit stronger and more widely dispersed two‐photon absorption (2PA) than those of dithienothiophene (DTT)‐based congeners. As a consequence, the bithiophene‐conjugated TTA chromophore exhibits the highest maximum 2PA cross‐section value (up to 2500 GM) with good thermal stability, and thus, it is the best performing two‐photon chromophore among the studied model compounds. The bithiophene‐conjugated DTT analogue exhibits the second highest maximum two‐photon absorptivity of 1950 GM, which is nearly 7 times larger than that of previously reported DTT‐based chromophores. 相似文献
BODIPY dyes have attracted considerable attention as potential photosensitizers in dye‐sensitized solar cells (DSSCs) owing to their excellent optical properties and facile structural modification. This account focuses on recent advances in the molecular design of D‐π‐A BODIPY dyes for applications in DSSCs. Special attention has been paid to the structure‐property relationships of D‐π‐A BODIPY dyes for DSSCs. The developmental process in the modified position at the BODIPY core with a donor/acceptor is described. The devices based on 2,6‐modified BODIPY dyes exhibit better photovoltaic performance over other modified BODIPY dyes. Meanwhile, the research reveals the correlation of molecular structures (various donor chromophores, extended units, molecular frameworks, and long alkyl groups) with their photophysical and electrochemical properties and relates it to their performance in DSSCs. The structure‐property relationships give valuable information and guidelines for designing new D‐π‐A BODIPY dyes for DSSCs.
A series of D ‐π‐A organic dendritic and star‐shaped molecules based on three various chromophores (i.e., the truxene nodes, triphenylamine moieties as the donor, and benzothiadiazole chromophore as the acceptor) and their corresponding model compounds are facilely developed. Their photophysical and electrochemical properties are investigated in detail by UV/Vis absorption and photoluminescent spectroscopy, and cyclic voltammetry. By changing the various conjugated spacers (i.e., single bond, double bond, and triple bond) among the three chromophores of dendritic series, their photophysical properties (that is, the one‐photon absorption range and two‐photon absorption cross‐section values) are effectively modulated. All D ‐π‐A conjugated oligomers show a broad and strong absorption band from 250 to 700 nm in thin films. Solution‐processed bulk‐heterojunction photovoltaic devices using our oligomer as donor and PCBM as acceptor are fabricated and measured. The power conversion efficiency of the devices based on our oligomers continuously increases from DBTTr to TRTD2A as a result of an increasing relative absorption intensity in longer wavelength region by changing the donor‐acceptor ratio and conjugated spacers between the donor and acceptor. The power conversion efficiency of the devices based on TRTD2A was 0.54 % under the illumination of AM 1.5 and 100 mW cm?2, which is the highest value recorded based on D ‐π‐A conjugated oligomers containing triphenylamine moieties and benzothiadiazole chromophores with truxene to date. 相似文献
A convenient method for synthesizing α‐(1,2,4‐triazolo[1,5‐a]pyrimidine‐2‐sulfonyl)methane derivatives, 3 and 4 , by the well known Knoevenagel reaction, in one step, is described. The two chromophores are stilbene‐type chromophores containing the same D‐π‐A structures and end‐capped with aromatic group as their donors. Measured with femtosecond multipass Ti:sapphire amplifier as irradiation source (pumped by the laser at 800 nm), the two chromophores show efficient two‐photon induced orange red fluorescence emission. The experimental results indicate that the numbers of branches of the two chromophores affect their one‐photon properties and two‐photon up‐conversion emission behaviors, and with the increasing numbers of branches, their wavelengths of λabsmax, λspfmax and λtpfmax exhibit bathochromic shifts. 相似文献
Three two‐photon absorption (TPA) tribranched chromophores were successfully prepared, in which 1,3,5‐triazine is been as electron deficient core, 1,4‐phenylenedivinylene as conjugated bridge, 3,4‐ethylenedioxythiophene (EDOT) ( T1 ), N‐methylpyrrole ( T2 ) or triphenylamine ( T3 ) as electron‐donating end‐groups. Their photophysical properties were studied by absorption, one‐ and two‐photon fluorescence and TPA cross‐section determination. The nonlinear transmission (NLT) measurement in femtoseconds (fs) regime at 800 nm indicates that TPA cross‐section (2 values of T1 , T2 and T3 with extended Π‐conjugated bridge are much larger than the corresponding chromophore T4 with a short length bridge, and TPA cross‐section of T1 with end‐groups EDOT exhibits a remarkable enhancement compared with T2 and T3 having the same length Π‐system. The chromophores T1 , T2 and T3 show also remarkable up‐converted luminescence and optical limiting activity. 相似文献