Transient Absorption Measurements Research Articles

Ultrafast Spectroelectrochemistry of the Catechol/o‐Quinone Redox Couple in Aqueous Buffer Solution

AbstractEumelanin is a natural pigment found in many organisms that provides photoprotection from harmful UV radiation. As a redox‐active biopolymer, the structure of eumelanin is thought to contain different redox states of quinone, including catechol subunits. To further explore the excited state properties of eumelanin, we have investigated the catechol/o‐quinone redox couple by spectroelectrochemical means, in a pH 7.4 aqueous buffered solution, and using a boron doped diamond mesh electrode. At pH 7.4, the two proton, two electron oxidation of catechol is promoted, which facilitates continuous formation of the unstable o‐quinone product in solution. Ultrafast transient absorption (femtosecond to nanosecond) measurements of o‐quinone species involve initial formation of an excited singlet state followed by triplet state formation within 24 ps. In contrast, catechol in aqueous buffer leads to formation of the semiquinone radical Δt>500 ps. Our results demonstrate the rich photochemistry of the catechol/o‐quinone redox couple and provides further insight into the excited state processes of these key building blocks of eumelanin.

Hydrophilic Photocrosslinkers as a Universal Solution to Endow Water Affinity to a Polymer Photocatalyst for an Enhanced Hydrogen Evolution Rate.

A universal approach for enhancing water affinity in polymer photocatalysts by covalently attaching hydrophilic photocrosslinkers to polymer chains is presented. A series of bisdiazirine photocrosslinkers, each comprising bisdiazirine photophores linked by various aliphatic (CL-R) or ethylene glycol-based bridge chains (CL-TEG), is designed to prevent crosslinked polymer photocatalysts from degradation through a safe and efficient photocrosslinking reaction at a wavelength of 365nm. When employing the hydrophilic CL-TEG as a photocrosslinker with polymer photocatalysts (F8BT), the hydrogen evolution reaction (HER) rate is considerably enhanced by 2.5-fold compared to that obtained using non-crosslinked F8BT photocatalysts, whereas CL-R-based photocatalysts yield HER rates comparable to those of non-crosslinked counterparts. Photophysical analyses including time-resolved photoluminescence and transient absorption measurements reveal that adding CL-TEG accelerates exciton separation, forming long-lived charge carriers. Additionally, the in-depth study using molecular dynamics simulations elucidates the dual role of CL-TEG: it enhances water penetration into the polymer matrix and stabilizes charge carriers after exciton generation against undesirable recombination. Therefore, the strategy highlights endowing a high-permittivity environment within polymer photocatalyst in a controlled manner is crucial for enhancing photocatalytic redox reactivity. Furthermore, this study shows that this hydrophilic crosslinker approach has a broad applicability in general polymer semiconductors and their nanoparticulate photocatalysts.

Photoinduced carrier transfer dynamics in a monolayer MoS2/PbS quantum dots heterostructure

Two-dimensional molybdenum disulfide (MoS2) has been proven to be a candidate in photodetectors, and MoS2/lead sulfide (PbS) quantum dots (QDs) heterostructure has been used to expand the optical response wavelength of MoS2. Time-resolved pump-probe transient absorption measurements are performed to clarify the carrier transfer dynamics in the MoS2/PbS heterostructure. By comparing the carrier dynamics in MoS2 and MoS2/PbS under different pump wavelengths, we found that the excited electrons in PbS QDs can transfer rapidly (<100 fs) to MoS2, inducing its optical response in the near-infrared region, although the pump light energy is lower than the bandgap of MoS2. Besides, interfacial excitons can be formed in the heterostructure, prolonging the lifetime of the excited carriers, which could be beneficial for the extraction of the carriers in devices.

High Electronic Coupling between Cu Complexes and Oxidized Dyes Confirmed by Measurements of Driving Force Dependent Regeneration Kinetics in Minimal Electrolyte System.

We confirm fast regeneration kinetics between copper complexes and oxidized organic dyes and the major contribution of electronic coupling (HDA). The highest efficiency of dye-sensitized TiO2 solar cells has been shown by employing Cu complex redox couples. Various groups have reported a fast regeneration rate of oxidized dyes by Cu complexes giving a low driving force attributed to low reorganization energy (λ), but the effect of HDA has not been evaluated. The values of HDA and λ can be derived from driving force dependent transient absorption (TA) measurements. However, analyzing TA decay using Cu complexes is not trivial because accelerated recombination by the presence of Cu2+ complexes and biphasic TA decay often complicates the analysis. Here we employ 16 Cu1+ and Co2+ complexes and two dyes. To simplify the system, i.e., making a minimal electrolyte system, Cu2+ and Co3+ complexes and a common additive of 4-tert-butylpyridine are not used. From the driving force dependent TA decays of oxidized dyes by both Cu1+ and Co2+ complexes, λ for the combination of the Cu complexes and dyes is found to be about 0.15 eV lower than that of Co complexes. Approximately 3 to 5 times higher HDA values of Cu complexes than those of Co complexes are obtained, which is the dominant factor for faster rates. The values vary with the structure of the molecules, showing the possibility of increasing the HDA values further. The higher HDA values of a Cu complex than that of a Co complex are also reproduced by quantum chemical calculations.

Energy Transfer-Dominated Quasi-2D Blue Perovskite Light-Emitting Diodes.

The bromide-chloride mixed quasi-two-dimensional (2D) perovskite, with a natural quantum well structure and tunable exciton binding energy, has gained significant attention for high-performance blue perovskite light-emitting diodes (PeLEDs). However, the relative importance of having a low trap state density or efficient exciton transfer for high-efficiency electroluminescence (EL) performance remains elusive. Here, two molecules with the benzoic acid group, sodium 4-fluorobenzoate (SFB) and 3,5-dibromobenzoic acid (DBA), are used to modulate the phase distribution and trap state to explore the effect between energy transfer and defect passivation. As a result, when the n = 1 phase is inhibited in both films, the DBA@SFB-modified perovskite films achieve a higher photoluminescence quantum yield (PLQY) than the SFB-modified perovskite films due to effective defect passivation. However, DBA@SFB-modified PeLEDs exhibit lower external quantum efficiency (EQE) compared to SFB-modified PeLEDs due to the poor exciton transfer between the low-dimensional phase. This demonstrates that passivation strategies may enhance photoluminescence through reducing nonradiative recombination, but the effect of phase distribution is pivotal for EL performance by efficient energy transfer in quasi-2D perovskites. Femtosecond time-resolved transient absorption measurements confirm the fastest carrier dynamics in SFB-modified perovskite films, further corroborating the above result. This work provides useful information about phase modulation and defect passivation for high-efficiency blue quasi-2D PeLEDs.

A Bis-Porphyrin Cavitand Breathing-In to Constrict Bucky Balls.

Bis-porphyrin cages have long been exploited to bind fullerenes selectively for various applications. The major consideration for an effective binding here had been the cavity size. Herein, we structurally demonstrate that a bis-Ni-porphyrin cavitand having even a smaller cavity can host a larger fullerene by a breathing and ruffling mechanism. It has also been shown that both the electronic and steric influence at the meso- positions of the porphyrin in fact dictate the binding character. The smaller cavity of 2NiD exhibits preferential binding for C70 over C60; however, surprisingly, the larger cavities in 2HD and 2NiTD display stronger affinities for C60 over the larger fullerene. We show here that the structural elasticity infused both by the metalloporphyrins and the connecting bridges play a major role in directing the binding. These conclusions have adequately been supported by structural and spectroscopic investigations. Additionally, the suitability of one of the conjugates for photoinduced charge-separation has been investigated using ultrafast transient absorption measurements. 2NiD has a charge separation timescale of ~0.8 ps, while charge recombination occurs at a longer timescale of ~920 ps.

Revealing photoluminescence and nonlinear optical absorption characteristics of PbMo0.75W0.25O4 single crystal for optical limiting applications

Nonlinear absorption properties of PbMo0.75W0.25O4 single crystal fabricated by the Czochralski method were studied. The band gap energy of the crystal was determined as 3.12 eV. Urbach energy which represents the defect states inside the band gap was found to be 0.106 eV. PbMo0.75W0.25O4 single crystal has a broad photoluminescence emission band between 376 and 700 nm, with the highest emission intensity occurring at 486 nm and the lowest intensity peak at 547 nm, depending on the defect states. Femtosecond transient absorption measurements reveal that the lifetime of localized defect states is found to be higher than the 4 ns pulse duration. Open aperture (OA) Z-scan results demonstrate that the PbMo0.75W0.25O4 single crystal exhibits nonlinear absorption (NA) that includes two-photon absorption (TPA) as the dominant mechanism at the 532 nm excitations corresponding to 2.32 eV energy. NA coefficient (β eff ) increased from 7.24 × 10−10 m W−1 to 8.81 × 10−10 m W−1 with increasing pump intensity. At higher intensities β eff tends to decrease with intensity increase. This decrease is an indication that saturable absorption (SA) occurred along with the TPA, called saturation of TPA. The lifetime of the defect states was measured by femtosecond transient absorption spectroscopy. Saturable absorption behavior was observed due to the long lifetime of the localized defect states. Closed aperture (CA) Z-scan trace shows the sign of a nonlinear refractive index. The optical limiting threshold of PbMo0.75W0.25O4 single crystal at the lowest intensity was determined as 3.45 mJ/cm2. Results show that the PbMo0.75W0.25O4 single crystal can be a suitable semiconductor material for optical limiting applications in the visible region.

Effect of niobium doping on excitonic dynamics in MoSe2

Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe2 as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe2 across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.

Enhancing Carrier Transport in 2D/3D Perovskite Heterostructures through Organic Cation Fluorination.

The interfacial 2D/3D perovskite heterostructures have attracted extensive attention due to their unique ability to combine the high stability of 2D perovskites with the remarkable efficiency of 3D perovskites. However, the carrier transport mechanism within the 2D/3D perovskite heterostructures remains unclear. In this study, the carrier transport dynamics in 2D/3D perovskite heterostructures through a variety of time-resolved spectroscopic measurements is systematically investigated. Time-resolved photoluminescence results reveal nanosecond hole transfer from the 3D to 2D perovskites, with enhanced efficiency through the introduction of fluorine atoms on the phenethylammonium (PEA) cation. Transient absorption measurements unveil the ultrafast picosecond electron and energy transfer from 2D to 3D perovskites. Furthermore, it is demonstrated that the positioning of fluorination on the PEA cations effectively regulates the efficiency of charge and energy transfer within the heterostructures. These insightful findings shed light on the underlying carrier transport mechanism and underscore the critical role of cation fluorination in optimizing carrier transport within 2D/3D perovskite heterostructure-based devices.

Photosensitizers Based on Bichromophoric Dyads Combining Ru(II)-Polypyridyl Complexes and Dissymmetric Perylene Monoimide Derivatives: The Nontrivial Role of Ligand Substitution.

The covalent modification of Ru(II) polypyridyl complexes (RPCs) with organic chromophores is a powerful strategy to obtain metal-based photosensitizer agents (PSs) with improved performance for application in photodynamic therapy (PDT). In this respect, perylene-imides are of particular interest due to their rich chemical-physical repertoire, and it is therefore quite surprising that their combination with RPCs has been poorly considered so far. Herein, we report on the photophysical behavior of two newly synthesized RPCs bearing a perylene monoimide appendant (PMI-Ad). Differently from the majority of RPCs-perylene-imides dyads, these chromophores are dissymmetric and are tethered to the metal centers through a single C-C bond in the 3- or 5-position of 1,10-phenanthroline (Ru-3PMI-Ad and Ru-5PMI-Ad). Both compounds show excellent singlet oxygen photosensitizing activity, with quantum yields reaching >90% in the case of Ru-3PMI-Ad. A combined spectroscopic and theoretical analysis, also involving transient absorption and luminescence lifetime measurements, demonstrates that both compounds undergo intersystem crossing on a very fast time scale (tens of picoseconds) and with high efficiency. Our results further demonstrate that the increased electron delocalization between the metal center and the PMI-Ad chromophore observed for Ru-3PMI-Ad additionally contributes to increase the singlet oxygen quantum yields by prolonging the lifetime of the triplet state.

"Giant" Colloidal Quantum Well Heterostructures of CdSe@CdS Core@Shell Nanoplatelets from 9.5 to 17.5 Monolayers in Thickness Enabling Ultra-High Gain Lasing.

Semiconductor colloidal quantum wells (CQWs) have emerged as a promising class of gain materials to be used in colloidal lasers. Although low gain thresholds are achieved, the required high gain coefficient levels are barely met for the applications of electrically-driven lasers which entails a very thin gain matrix to avoid charge injection limitations. Here, "giant" CdSe@CdS colloidal quantum well heterostructures of 9.5 to 17.5 monolayers (ML) in total with corresponding vertical thickness from 3.0 to 5.8nm that enable record optical gain is shown. These CQWs achieve ultra-high material gain coefficients up to ≈140000cm-1 , obtained by systematic variable stripe length (VSL) measurements and independently validated by transient absorption (TA) measurements, owing to their high number of states. This exceptional gain capacity is an order of magnitude higher than the best levels reported for the colloidal quantum dots. From the dispersion of these quantum wells, low threshold amplified spontaneous emission in water providing an excellent platform for optofluidic lasers is demonstrated. Also, employing these giant quantum wells, whispering gallery mode (WGM) lasing with an ultra-low threshold of 8µJcm-2 is demonstrated. These findings indicate that giant CQWs offer an exceptional platform for colloidal thin-film lasers and in-solution lasing applications.

Exciton dynamics in two-dimensional metal halide perovskite: The impact of film processing.

We investigate the hot carrier and exciton dynamics in two-dimensional (2D) metal halide perovskites using time-resolved spectroscopy. 2D perovskite films were prepared with and without dimethyl sulfoxide treatment to elucidate the effect of film processing techniques on optoelectronic properties. Femtosecond transient absorption measurements reveal that the charge carrier dynamics are different in the two samples, and excitons survive for a longer time in the treated sample than the untreated one. While the early-time carrier dynamics in the untreated sample are dominated by charges trapped by defect states, the hot free carriers govern the dynamics in the treated sample due to fewer defects in it. Morphological and other spectroscopic studies, including time-resolved photoluminescence, further suggest the formation of more defects in the untreated sample. These results can guide the future development of efficient 2D perovskite-based optoelectronic devices.

B(I)‐Site Alkali Metal Engineering of Lead‐Free Perovskite Nanocrystals for Efficient X‐Ray Detection and Imaging

AbstractLead‐free metal halide double perovskites have emerged as promising scintillators owing to their superior optoelectronic properties, low‐cost and solution processability. However, it is still challenging to develop high‐performance flexible X‐ray scintillators based on the B(I)‐site alkali metal modulation in lead‐free double perovskite nanocrystals (NCs). Herein, a series of novel Cs2B(I)GdCl6 (B: Li, Na, K) of double perovskite A2B(I)M(III)X6 NCs structures are successfully synthesized, the optical and scintillator properties of which are significantly sensitive to the B(I)‐site alkali metals with the doping of Sb3+. They showed efficient self‐trapped exciton (STE) emission with high photoluminescence quantum yield (PLQY) and exhibited the highest X‐ray detection limit (86 nGyair s−1) and excellent spatial resolutions (>15 lp mm−1). The femtosecond transient absorption measurement and theoretical analysis further revealed that the B(I)‐site alkali metal fundamentally balanced the exciton–phonon coupling with appropriate STEs formation energy barrier and the electron localization and thus improved the optical and scintillator properties. This B(I)‐site alkali metal engineering offers a strategy to develop bright luminescent double perovskite NCs for X‐ray detection and imaging devices.

Energy transfer enhanced photoluminescence of 2D/3D CsPbBr3 hybrid assemblies.

Energy transfer has been proven to be an effective method to optimize optoelectronic conversion efficiency by improving light absorption and mitigating nonradiative losses. We prepared 2D/3D CsPbBr3 hybrid assemblies at different reaction temperatures using the hot injection method and found that the photoluminescence quantum yields (PLQYs) of these hybrids were greatly enhanced from 53.4% to 72.57% compared with 3D nanocrystals (NCs). Femtosecond transient absorption measurements were used to study the PLQY enhancement mechanisms, and it was found that the hot carrier lifetime improved from 0.36 to 1.88ps for 2D/3D CsPbBr3 hybrid assemblies owing to the energy transfer from 2D nanoplates to 3D NCs. The energy transfer benefits the excited carrier accumulation and prolonged hot carrier lifetime in 3D NCs in hybrid assemblies, as well as PLQY enhancement in materials.

Anomalous proton transfer of a photoacid HPTS in nonaqueous reverse micelles.

The proton transfer reaction is one of the fundamental chemical reactions where the reaction dynamics strongly depend on solvent properties such as acidity or basicity. A photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) shows a sharp decrease of pKa (7.7 → 0.5) upon photoexcitation, and the excited-state proton transfer (ESPT) occurs with ultrafast time constants of 2.5 and 89 ps in bulk aqueous solution. However, the two-step proton transfers via the contact ion pair formation and the proton diffusion are strongly limited inside the nanopools of reverse micelles (RMs). The confinement in small RMs strongly impeded the proton transfer reactions. In this work, we report the ESPT of HPTS confined in methanol-in-oil RMs by steady-state and time-resolved electronic spectroscopy. Interestingly, HPTS shows substantial deprotonation in the excited state only in small RMs, while the ESPT of HPTS does not occur in bulk methanol solution due to the low basicity of aliphatic alcohols. The kinetic analysis of time-resolved fluorescence and transient absorption measurements will compare the proton transfer dynamics of HPTS in the water-in-oil and methanol-in-oil RMs. The ESPT of photoacids, especially in the nonaqueous RMs, can be crucial in understanding many important chemical reactions involving proton transfer in the confined environments of cells and membranes.

Study on interface engineering and chemical bonding of the ReS2@ZnO heterointerface for efficient charge transfer and nonlinear optical conversion efficiency.

Rhenium sulfide (ReS2) has emerged as a promising two-dimensional material, demonstrating broad-spectrum visible absorption properties that make it highly relevant for diverse optoelectronic applications. Manipulating and optimizing the pathway of photogenerated carriers play a pivotal role in enhancing the efficiency of charge separation and transfer in novel semiconductor composites. This study focuses on the strategic construction of a semiconductor heterostructure by synthesizing ZnO on vacancy-containing ReS2 (VRe-ReS2) through chemical bonding processes. The ingeniously engineered built-in electric field within the heterostructure effectively suppresses the recombination of photogenerated electron-hole pairs. A direct and well-established interfacial connection between VRe-ReS2 and ZnO is achieved through a robust Zn-S bond. This distinctive bond configuration leads to enhanced nonlinear optical conversion efficiency, attributed to shortened carrier migration distances and accelerated charge transfer rates. Furthermore, theoretical calculations unveil the superior chemical interactions between Re vacancies and sulfide moieties, facilitating the formation of Zn-S bonds. The photoluminescence (PL) intensity is increased by the formation of VRe-ReS2 and ZnO heterostructure and the PL quantum yield of VRe-ReS2 is improved. The intricate impact of the Zn-S bond on the nonlinear absorption behavior of the VRe-ReS2@ZnO heterostructure is systematically investigated using femtosecond Z-scan techniques. The charge transfer from ZnO to ReS2 defect levels induces a transition from saturable absorption to reverse saturable absorption in the VRe-ReS2@ZnO heterostructure. Transient absorption measurements further confirm the presence of the Zn-S bond between the interfaces, as evidenced by the prolonged relaxation time (τ3) in the VRe-ReS2@ZnO heterostructure. This study offers valuable insights into the rational construction of heterojunctions through tailored interfacial bonding and surface/interface charge transfer pathways. These endeavors facilitate the modulation of electron transfer dynamics, ultimately yielding superior nonlinear optical conversion efficiency and effective charge regulation in optoelectronic functional materials.

Inhibition of ion diffusion/migration in perovskite p-n homojunction by polyetheramine insert layer to enhance stability of perovskite solar cells with p-n homojunction structure.

Perovskite p-n homojunctions (PHJ) have been confirmed to play a crucial role in facilitating carrier separation/extraction in the perovskite absorption layer and provide an additional built-in potential, which benefits the inhibition of carrier recombination in perovskite solar cells (PSCs) and ultimately improves device performance. However, the diffusion and migration of ions between n-type and p-type perovskite films, particularly under operational and heating conditions, lead to the degradation of PHJ structures and limit the long-term stability of PSCs with PHJ structure (denoted as PHJ-PSCs). In this study, we propose an insert layer strategy by directly introducing an ultra-thin polyetheramine (PEA) layer between the n-type and p-type perovskite films to address those challenges arising from ion movements. Femtosecond transient absorption (fs-TAS) and photoluminescence (PL) measurements demonstrate that the PHJ (without and with the insert layer) enhances carrier separation/extraction compared to the single n-type perovskite film. Monitoring the evolution of bromine element distribution reveals that the insert layer can efficiently suppress ion diffusion between perovskite films, even under long-term illumination and heating conditions. Consequently, an efficiency of 23.53% with excellent long-term operational stability is achieved in the optimized PHJ-PSC with the insert layer.

Highly stable CsPbBr3/ PMA perovskite nanocrystals for improved optical performance

In this study, to address the stability issues, we synthesized a CsPbBr3-coated poly (maleic anhydride-alt-1-octadecene) (CsPbBr3/PMA) using a modified hot-injection method. The CsPbBr3/PMA perovskite nanocrystals (PNCs) exhibited effective green emission at 522 nm with an improved photoluminescence quantum yield (86.8 %) compared to traditional CsPbBr3 PNCs (54.2 %). The ligands in the polymer coating can bond with the uncoordinated Pb and Br ions on the surface of PNCs to minimize surface defects and avoid exposure to the external environment, enhancing the stability of the perovskites. Time-resolved photoluminescence spectra showed longer lifetimes for CsPbBr3/PMA PNCs, while transient absorption measurements provided valuable insights into the intraband hot-exciton relaxation and recombination. We demonstrate the potential application of CSPbBr3/PMA in a down-conversion white-light-emitting diode (LED) by coupling green CsPbBr3/PMA and red K2SiF6:Mn4+ phosphor-coated glass slides onto a 455-nm blue GaN LED. The white LED produced a white light with the International Commission on Illumination color coordinates of (0.323, 0.345), luminous efficiency of 58.4 lm/W, and color rendering index of 83.2. The fabricated, white-LED system obtained a wide color gamut of 125.3 % of the National Television Standards Committee and 98.9 % of Rec. 2020. The findings demonstrate that CsPbBr3/PMA can be an efficient down-conversion material for white LEDs and backlighting.

Enhanced Photocatalytic Activity of Cs4PbBr6/WS2 Hybrid Nanocomposite

Photocatalytic processes are among the prime means for mitigating the pollution caused by toxic effluents. In this context, photocatalysis presents a promising path and is undergoing rapid evolution. Halide perovskite‐nanocrystals (HP‐NCs) are excellent candidates due to their negative conduction band minimum and low work function, essential for photocatalysis. Yet, HP‐NCs face limitations within this domain because they are prone to chemical degradation when exposed to external factors like high temperature, polar solvents, oxygen, and light. A practical approach toward stabilizing HP‐NCs involves hybridizing them with a chemically inert material that can provide steric stabilization and act as a cocatalyst. Transition‐metal dichalcogenides emerge as outstanding candidates to sterically stabilize the HPs as they are stable, chemically inert, and can serve as co‐catalysts, enabling suppressed charge recombination. Herein, the photocatalytic performance of Cs4PbBr6/WS2‐nanocomposites towards organic dye degradation in polar solvents under visible light illumination is investigated. We found that the presence of WS2 nanostructures significantly stabilizes the HP‐NCs and promotes dye degradation rate compared to pristine Cs4PbBr6‐NCs. Using transient absorption measurements, we found that the WS2‐nanostructures act as an electron transport channel, effectively reducing charge recombination in the NCs. These findings pave the way for implementing Cs4PbBr6/WS2‐nanocomposites as stable and superior photocatalysts.

Nanographene-Fused Expanded Carbaporphyrin Tweezers.

A nanographene-fused expanded carbaporphyrin (5) and its BF2 complex (6) were synthesized. Single-crystal X-ray structures revealed that 5 and 6 are connected by two hexa-peri-hexabenzocoronene (HBC) units and two dipyrromethene or BODIPY units, respectively. As prepared, 5 and 6 both show nonaromatic character with figure-of-eight carbaoctaphyrin (1.1.1.0.1.1.1.0) cores and adopt tweezers-like conformations characterized by a partially confined space between the two constituent HBC units. The distance between the HBC centers is >10 Å, while the dihedral angles between the two HBC planes are 30.5 and 35.2° for 5 and 6, respectively. The interactions between 5 and 6 and fullerene C60 were studied both in organic media and in the solid state. Proton NMR spectral titrations of 5 and 6 with C60 revealed a 1:1 binding mode for both macrocycles. In toluene-d8, the corresponding binding constants were determined to be 1141 ± 17 and 994 ± 10 M-1 for 5 and 6, respectively. Single-crystal X-ray diffraction structural analyses confirmed the formation of 1:1 fullerene inclusion complexes in the solid state. The C60 guests in both complexes are found within triangular pockets composed of two HBC units from the tweezers-like receptor most closely associated with the bound fullerene, as well as an HBC unit from an adjacent host. Femtosecond transient absorption measurements revealed subpicosecond ultrafast charge separation between 5 (and 6) and C60 in the complexes. To the best of our knowledge, the present report provides the first example wherein a nanographene building block is incorporated into the core of a porphyrinic framework.