Fluorene Donor Research Articles

Near-infrared harvesting metal-free organic dyes for transparent DSSCs: A theoretical design approach

In this study, we employed density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to optimize near-infrared (NIR) harvesting dyes, gaining deeper insights into their structure–property relationship, particularly for dye-sensitized solar cells (DSSCs). Our focus was on fine-tuning electron-donating and withdrawing groups within D-π-A metal-free organic dyes to enhance NIR absorption and achieve visually transparent DSSCs. Our research revealed a significant redshift in dyes based on isoindigo derivatives, with thiophene (TII) as the π-spacer. Dyes incorporating fluorene as the donor group effectively mitigated charge recombination rates, a key challenge in low-bandgap molecules. Notably, the TII1 dye, combining a fluorene donor with a TII π-spacer, exhibited maximum absorption at 654 nm and transmitted substantial visible light (500–600 nm), making it suitable for use in visually transparent DSSCs. These findings underscore the potential of the TII1 dye in significantly advancing the development of visibly transparent DSSCs.

Simple metal-free dyes derived from fluorene for visually transparent solar cells: A comparative study of different anchoring groups and electrolytes

We present a straightforward synthesis of UV-harvesting dyes featuring a fluorene donor with different anchoring groups, such as cyano acetic acid, amino benzoic acid, and 2-methyl-quinoline-6-carboxylic acid (designated as FCA, FAB, and FQA, respectively). We comprehensively investigate the spectroscopic, electrochemical and colorific properties of these dyes and evaluate their suitability as photosenstizers in visually transparent and colorless dye-sensitized solar cells (DSSCs). FCA and FQA possessing planar geometries exhibit remarkably efficient collection of UV photons, leading to excellent power-conversion-efficiencies (PCEs) under UVA radiation. Furthermore, we explore the incorporation of the binary redox couple, (I−,Br−)/(I3−,I2Br−), to enhance the ability to transmit visible light, positively impacting their color rendering properties, while preserving their light harvesting capacities.

UV-harvesting dyes featuring a fluorene donor for visibly transparent and colorless dye-sensitized solar cells

We report the facile synthesis of UV-harvesting dyes featuring a fluorene donor with different π-conjugation bridges. Moreover, we determine the spectroscopic, electrochemical and colorific properties of the dyes and verify their applicability as photosensitizers in visibly transparent and colorless dye-sensitized solar cells. The UV-selective and visibly transparent solar cells exhibit a power conversion efficiency of 0.91%–2.70% under one sun illumination (100 mW/m2) and 6.17%–8.13% under UVA (365 nm, 115.22 mW/m2), with the corresponding visible light transmittance of 60.73%–58.22% and general color rendering index of 91–90.

Highly Efficient Deep-Blue OLEDs using a TADF Emitter with a Narrow Emission Spectrum and High Horizontal Emitting Dipole Ratio.

New blue (DBA-SAB) and deep-blue (TDBA-SAF) thermally activated delayed fluorescence (TADF) emitters are synthesized for blue-emitting organic-light emitting diodes (OLEDs) by incorporating spiro-biacridine and spiro-acridine fluorene donor units with an oxygen-bridged boron acceptor unit, respectively. The molecules show blue and deep-blue emission because of the deep highest occupied molecular energy levels of the donor units. Besides, both emitters exhibit narrow emission spectra with the full-width at half maximum (FWHM) of less than 65nm due to the rigid donor and acceptor units. In addition, the long molecular structure along the transition dipole moment direction results in a high horizontal emitting dipole ratio over 80%. By combining the effects, the OLED utilizing DBA-SAB as the emitter exhibits a maximum external quantum efficiency (EQE) of 25.7% and 1931 Commission Internationale de l'éclairage (CIE) coordinates of (0.144, 0.212). Even a higher efficiency deep blue TADF OLED with a maximum EQE of 28.2% and CIE coordinates of (0.142, 0.090) is realized using TDBA-SAF as the emitter.

An all-small-molecule organic solar cell derived from naphthalimide for solution-processed high-efficiency nonfullerene acceptors

Two small molecules BYG-1 and BYG-2 with fluorene donor and benzothiadiazole acceptor units connected to the terminal naphthamide group via ethyne linker were designed and synthesized.

1, 3-Indanedione functionalized fluorene luminophores: Negative solvatochromism, nanostructure-morphology determined AIE and mechanoresponsive luminescence turn-on

Luminous efficiency in polar environment and aggregated state, as well as high-contrast luminescence on/off switching under external stimuli are significant issues to be addressed in developing functional fluorescent materials. Combining the advantages of solvatochromic effect in intramolecular charge transfer (ICT) compounds with their nanostructured morphological effects, we herein report a series of A–π–D–π–A fluorene derivatives, which simultaneously exhibit negative solvatochromism, aggregation-induced emission (AIE) and mechanoresponsive luminescence (MRL) turn-on. These molecules contain the same fluorene donor (D) and 1,3-indandione acceptor (A) but differ in alkyl substituents in the 9-position of the fluorene segment, including 9,9-dibutyl (b-DIPF), 9,9-dioctyl (o-DIPF) and 9,9-didodecyl (d-DIPF). The emission colors of these compounds were changed from blue to orange-red, and the fluorescence quantum yields increased upon increasing the solvent polarity from nonpolar hexane to polar dimethyl sulfoxide. Due to the formed random nanostructured aggregates, the compounds exhibited AIE characteristics in THF/H2O mixtures. Oppositely, their emission quenched 0D particles which were afforded by quick evaporation of their dichloromethane solvents under vacuum displayed remarkable mechanoresponsive luminescence turn-on behavior. Our results suggest that rationally design ICT molecules and control their nanostructures would be promising way for realizing multifunctional fluorescent materials.

An alternating copolymer of fluorene donor and quinoxaline acceptor versus a terpolymer consisting of fluorene, quinoxaline and benzothiadiazole building units: synthesis and characterization

An alternating polyfluorene copolymer based on fluorene donor and quinoxaline acceptor (P1) and an alternating terpolymer (P2) with fluorene (50 %) donor and quinoxaline (25 %) and benzothiadiazole (25 %) acceptor units were designed and synthesized for use as photoactive materials in solar cells. The presence of benzothiadiazole unit in P2 increased the optical absorption coverage in the range of 350–600 nm, which is an interesting property and a big potential for achieving improved photovoltaic performances with judicious optimization of the devices. Solar cells were fabricated from 1:4 blends of polymers-PCBM[70] using o-dichlorobenzene (o-DCB) as processing solvent, and P1 showed a power conversion efficiency (PCE) of 3.18 %, with a short-circuit current density (J SC) of 7.78 mA/cm2, an open-circuit voltage (V OC) of 0.82 V, and a fill factor (FF) of 50 % while P2 showed an overall PCE of 2.14 % with corresponding J SC of 5.97 mA/cm2, V OC of 0.84 V and FF of 42 %. In general, P2 gave lower J SC and FF presumably due to the fine domain sizes of the polymer–PCBM[70] blend as seen from the atomic force microscopy (AFM) image which might have affected the charge carrier transport. Alternating (P1) and ternary (P2) conjugated polymers were designed, synthesized and used for fabrication of photovoltaic devices.

High Fluorescent Porphyrin-PAMAM-Fluorene Dendrimers

Two new classes of dendrimers bearing 8 and 32 fluorene donor groups have been synthesized. The first and second generations of these porphyrin-PAMAM-fluorene dendrimers were characterized by 1H-NMR, 13C-NMR, FTIR, UV-vis spectroscopy, elemental analyses and MALDI-TOF mass spectrometry. The UV-vis spectra showed that the individual properties of donor and acceptor moieties were preserved, indicating that the new dendrimers could be used as photosynthetic antennae. Furthermore, for fluorescent spectroscopy, these dendrimers showed good energy transfer.

Enhanced performance in bulk heterojunction solar cells with alkylidene fluorene donor by introducing modified PFN-OH/Al bilayer cathode

We report bulk heterojunction solar cells with benzothiadiazole-containing polyalkylidene fluorene (PAFBToBT) donors made by introducing 2,4,7,9-tetramethyldec-5-yne-4,7-diol (Surfynol 104)-doped poly[9,9-bis(6′-(diethanolamino)hexyl)-fluorene] (PFN-OH) as an interfacial layer to enhance power conversion efficiency (PCE) and stability. Surfynol 104 has amphiphilic characteristics, and it supports the formation of a homogeneous interfacial layer on the photoactive layer. In addition, the application of the Surfynol 104-doped PFN-OH interfacial layer prevented the decrease in absorption of photons in the photoactive layer and improved the photocurrent density (JSC) by increasing the electron mobility. Therefore, JSC and the fill factor increased to 10.5 mA cm−2 and 49%, respectively, and the calculated PCE was 4.8%. In addition, a modified bilayer cathode system was introduced to the PCDTBT and the P3HT-based PSCs, and the PCE improved to 5.3% and 3.9%, respectively. Moreover, the in-air stability was enhanced.

Synthesis of platinum complexes of fluorenyl-substituted porphyrins used as phosphorescent dyes for solution-processed organic light-emitting devices

Platinum(II) complexes of symmetrical meso-substituted A4-porphyrins bearing four fluorene donor moieties 5,10,15,20-tetra(4-(2 methyloxyfluorenyl)phenyl)porphyrin, referred to as TOFP, or eight fluorene arms, 5,10,15,20-octa(3,5-(2 methyloxyfluorenyl)phenyl)porphyrin, OOFP, were synthesised and characterised. The photophysical properties of the new compounds are reported and compared to those of PtTPP and PtTFP {TPP=tetraphenylporphyrin and TFP=tetra(2-fluorenyl)porphyrin}. The luminescence quantum yields of PtTOFP and PtOOFP are 11% and 4.2%, respectively, compared to 4.6% for the reference PtTPP and only 2.0% for the previously studied compound PtTFP. The electronic and optoelectronic behaviour of solution-processed organic light-emitting devices (OLEDs) are reported that incorporate these platinum porphyrins as phosphorescent dyes doped into different layers of a polyvinylcarbazole (PVK) host.

Molecular Engineering of a Fluorene Donor for Dye-Sensitized Solar Cells

To improve their efficiency beyond the state-of-the-art, D-pi-A dyes must display increased spectral breadth and account for the physical limitations observed in the dye. sensitized solar cells. In particular, they should be designed to control the electron-transfer processes that ensure efficient dye-regeneration and prevent undesired electron recombination. In this article, the electronic and steric properties of a fluorene donor are engineered to meet all these requirements. This elegant donor is featured along with a cyclopentadithiophene bridge and a cyanoacrylic acid acceptor in JF419. A thorough comparison with Y123 and C218 demonstrates the relevance of the design. Relative to conventional donors, the fluorene construct described here enhances the light harvesting properties, because of its exceptional electron donating character. The functionalities used to induce the electronic push through the D-pi-A structure also provide the dye with favorable steric properties. Indeed, the substitution around the fluorene core adequately insulates the TiO2 surface from the electrolyte, which prevents back-recombination and prolongs the electron lifetime in the semiconductor. Furthermore, compared to analogous dyes, JF419 maintains nearly quantitative regeneration efficiency, despite the lower regeneration driving force. The root of this observation is contributed to a significantly more delocalized hole in the photo-oxidized JF419(center dot+), which is highlighted through transient absorption spectroscopy and quantum chemical calculations. The design principles established are relevant to the development of more comprehensive sensitizers, as evidenced by the 10.3% efficiency obtained in cobalt-based liquid dye-sensitized solar cells.

Synthesis and characterization of thiazolothiazole-based polymers and their applications in polymer solar cells

A novel series of thiazolothiazole (Tz)-based copolymers, poly[9,9-didecylfluorene-2,7-diyl-alt-2,5-bis-(3-hexylthiophene-2-yl)thiazolo[5,4-d]thiazole] (P1), poly[9,9-dioctyldibenzosilole-2,7-diyl-alt-2,5-bis-(3-hexylthiophene-2-yl)thiazolo[5,4-d]thiazole] (P2), and poly[4,4′-bis(2-ethylhexyl)-dithieno[3,2-b:2′,3′-d]silole-alt-2,5-bis-(3-hexylthiophene-2-yl)thiazolo[5,4-d]thiazole] (P3), were synthesized for the use as donor materials in polymer solar cells (PSCs). The field-effect carrier mobilities and the optical, electrochemical, and photovoltaic properties of the copolymers were investigated. The results suggest that the donor units in the copolymers significantly influenced the band gap, electronic energy levels, carrier mobilities, and photovoltaic properties of the copolymers. The band gaps of the copolymers were in the range of 1.80–2.14 eV. Under optimized conditions, the Tz-based polymers showed power conversion efficiencies (PCEs) for the PSCs in the range of 2.23–2.75% under AM 1.5 illumination (100 mW/cm2). Among the three copolymers, P1, which contained a fluorene donor unit, showed a PCE of 2.75% with a short-circuit current of 8.12 mA/cm2, open circuit voltage of 0.86 V, and a fill factor (FF) of 0.39, under AM 1.5 illumination (100 mW/cm2). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis and photophysical properties of porphyrins with fluorenyl pendant arms

Symmetrical-A 4-porphyrins bearing four fluorene donor moieties TOFP (5,10,15,20-tetra(4-(2 methyloxyfluorenyl)phenyl)porphyrin) as well as eight fluorene arms OOFP (5,10,15,20-octa(3,5-(2-methyloxyfluorenyl)phenyl)porphyrin) were synthesized and characterized. Preliminary photophysical properties are reported. In comparison to the reference tetraphenylporphyrin TPP, the luminescence properties are slightly improved. The fluorescence quantum yields of tetrafluorenylporphyrin TOFP ( 1) and octafluorenylporphyrin OOFP ( 2) are 0.10 and 0.13, respectively.

Photophysics of photoconducting polymers with pendant bichromophores II: Electron and energy transfer photoprocesses in several carbazole—fluorene donor—acceptor bichromophoric systems based on the monomeric reference compounds

The intramolecular electron and energy transfer photoprocesses of several bichromophoric molecules containing the carbazolyl chromophore as electron donor and the polynitrofluorene or 9-dicyanomethylene fluorene chromophore as electron acceptor were studied by measurement of the luminescence spectra and electrochemical properties of the corresponding monochromophoric reference compounds. For all donor—acceptor systems considered, the Rehm-Weller free energy change is negative (Δ G ET < 0) and for the long-range dipole—dipole interactions between the chromophores, the Förster critical transfer distance R 0 ≈ 30 Å at 296 K. These values of Δ G ET and R 0 correspond to rate constants k q and k FT of the same order of magnitude ( i.e. approximately 10 11 – 10 13 s −1) in accordance with the strong fluorescence quenching of the carbazolyl chromophore found in all of the bichromophoric molecular systems studied.

The kinetics of the photochemical hydrogen abstraction in crystals of fluorene doped with acridine

Photoexcitation of acridine when doped in fluorene crystals leads to hydrogen abstraction from the central fluorene CH 2 group and formation of a radical pair product. Both, the radical pair formation and a newly detected high temperature decay channel of the acridine triplet state are thermally activated and exhibit a strong isotope effect upon deuteration of the fluorene donor CH 2 group. The analysis of the existing data shows that the two processes are not directly related and hence the triplet state is not the precursor of the radical pair formation.