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Synthetic strategies for electron-deficient meso-perfluoroalkylporphyrins bearing diverse functional groups are described. Scalable and efficient syntheses for 5-triisopropylsilylethynyl-10,15,20-tris(heptafluoropropyl)porphyrin and 5-triisopropylsilylethynyl-10,20-bis(heptafluoropropyl)porphyrin that equip meso-ethynyl functional groups via the bilane route have been established, along with a refined route to [5,15-bis(heptafluoropropyl)porphinato]zinc(II). meso-Position halogenation of [5,15-bis(heptafluoropropyl)porphinato]zinc(II) was achieved by selective meso-nitration and subsequent reduction, diazonium salt formation, and iodination reactions. Computational data describe the low energy excited states of these chromophores and the electronic structural factors that control reactivity of these meso-perfluoroalkyl substituted porphyrin complexes. meso-Functionalized [5-triisopropylsilylethynyl-10,20-bis(heptafluoropropyl)porphinato]zinc(II) and [5-iodo-10,20-bis(heptafluoropropyl)porphinato]zinc(II) building blocks lay the foundation for the construction of highly conjugated multiporphyrin arrays that feature electronic structural properties important for the development of n-type materials and high potential photooxidants.

Printed carbon nanotube thin-film transistors (CNT-TFTs) are candidates for flexible electronics with printability on a wide range of substrates. Among the layers comprising a CNT-TFT, the gate dielectric has proven most difficult to additively print owing to challenges in film uniformity, thickness, and post-processing requirements. Printed ionic dielectrics show promise for addressing these issues and yielding devices that operate at low voltages thanks to their high-capacitance electric double layers. However, the printing of ionic dielectrics in their various compositions is not well understood, nor is the impact of certain stresses on these materials. In this work, we studied three compositionally distinct ionic dielectrics in fully printed CNT-TFTs: the polar-fluorinated polymer elastomer PVDF-HFP; an ion gel consisting of triblock polymer PS-PMMA-PS and ionic liquid EMIM-TFSI; and crystalline nanocellulose (CNC) with a salt concentration of 0.05%. Although ion gel has been thoroughly studied, e-PVDF-HFP and CNC printing are relatively new and this study provides insights into their ink formulation, print processing, and performance as gate dielectrics. Using a consistent aerosol jet printing approach, each ionic dielectric was printed into similar CNT-TFTs, allowing for direct comparison through extensive characterization, including mechanical and electrical stress tests. The ionic dielectrics were found to have distinct operational dependencies based on their compositional and ionic attributes. Overall, the results reveal a number of trade-offs that must be managed when selecting a printable ionic dielectric, with CNC showing the strongest performance for low-voltage operation but the ion gel and elastomer exhibiting better stability under bias and mechanical stresses.

Control of the singlet-triplet energy gap (Δ

Understanding how the complex interplay among excitonic interactions, vibronic couplings, and reorganization energy determines coherence-enabled transport mechanisms is a grand challenge with both foundational implications and potential payoffs for energy science. We use a combined experimental and theoretical approach to show how a modest change in structure may be used to modify the exciton delocalization, tune electronic and vibrational coherences, and alter the mechanism of exciton transfer in covalently linked cofacial Zn-porphyrin dimers (meso-beta linked ABm-β and meso-meso linked AAm-m). While both ABm-β and AAm-m feature zinc porphyrins linked by a 1,2-phenylene bridge, differences in the interporphyrin connectivity set the lateral shift between macrocycles, reducing electronic coupling in ABm-β and resulting in a localized exciton. Pump-probe experiments show that the exciton dynamics is faster by almost an order of magnitude in the strongly coupled AAm-m dimer, and two-dimensional electronic spectroscopy (2DES) identifies a vibronic coherence that is absent in ABm-β. Theoretical studies indicate how the interchromophore interactions in these structures, and their system-bath couplings, influence excitonic delocalization and vibronic coherence-enabled rapid exciton transport dynamics. Real-time path integral calculations reproduce the exciton transfer kinetics observed experimentally and find that the linking-modulated exciton delocalization strongly enhances the contribution of vibronic coherences to the exciton transfer mechanism, and that this coherence accelerates the exciton transfer dynamics. These benchmark molecular design, 2DES, and theoretical studies provide a foundation for directed explorations of nonclassical effects on exciton dynamics in multiporphyrin assemblies.

The photoexcited triplet states of porphyrin architectures are of significant interest in a wide range of fields including molecular wires, nonlinear optics, and molecular spintronics. Electron paramagnetic resonance (EPR) is a key spectroscopic tool in the characterization of these transient paramagnetic states singularly well suited to quantify spin delocalization. Previous work proposed a means of extracting the absolute signs of the zero-field splitting (ZFS) parameters, D and E, and triplet sublevel populations by transient continuous wave, hyperfine measurements, and magnetophotoselection. Here, we present challenges of this methodology for a series of meso-perfluoroalkyl-substituted zinc porphyrin monomers with orthorhombic symmetries, where interpretation of experimental data must proceed with caution and the validity of the assumptions used in the analysis must be scrutinized. The EPR data are discussed alongside quantum chemical calculations, employing both DFT and CASSCF methodologies. Despite some success of the latter in quantifying the magnitude of the ZFS interaction, the results clearly provide motivation to develop improved methods for ZFS calculations of highly delocalized organic triplet states.

Electronic waste can lead to the accumulation of environmentally and biologically toxic materials and is a growing global concern. Developments in transient electronics—in which devices are designed to disintegrate after use—have focused on increasing the biocompatibility, whereas efforts to develop methods to recapture and reuse materials have focused on conducting materials, while neglecting other electronic materials. Here, we report all-carbon thin-film transistors made using crystalline nanocellulose as a dielectric, carbon nanotubes as a semiconductor, graphene as a conductor and paper as a substrate. A crystalline nanocellulose ink is developed that is compatible with nanotube and graphene inks and can be written onto a paper substrate using room-temperature aerosol jet printing. The addition of mobile sodium ions to the dielectric improves the thin-film transistor on-current (87 μA mm−1) and subthreshold swing (132 mV dec−1), and leads to a faster voltage sweep rate (by around 20 times) than without ions. The devices also exhibit stable performance over six months in ambient conditions and can be controllably decomposed, with the graphene and carbon nanotube inks recaptured for recycling (>95% recapture efficiency) and reprinting of new transistors. We demonstrate the utility of the thin-film transistors by creating a fully printed, paper-based biosensor for lactate sensing. All-carbon thin-film transistors—made using crystalline nanocellulose as a dielectric, carbon nanotubes as a semiconductor and graphene as a conductor—can be printed onto paper substrates and the constituent materials subsequently recycled.

Significance A major mechanism of evolution involves fusing genes that encode single-domain proteins to create multidomain structures that achieve new functions. Here, we develop methods to design multidomain proteins entirely from scratch and achieve the premier de novo design of an allosterically regulated phenol oxidase that responds to the binding of a synthetic porphyrin., We describe the de novo design of an allosterically regulated protein, which comprises two tightly coupled domains. One domain is based on the DF (Due Ferri in Italian or two-iron in English) family of de novo proteins, which have a diiron cofactor that catalyzes a phenol oxidase reaction, while the second domain is based on PS1 (Porphyrin-binding Sequence), which binds a synthetic Zn-porphyrin (ZnP). The binding of ZnP to the original PS1 protein induces changes in structure and dynamics, which we expected to influence the catalytic rate of a fused DF domain when appropriately coupled. Both DF and PS1 are four-helix bundles, but they have distinct bundle architectures. To achieve tight coupling between the domains, they were connected by four helical linkers using a computational method to discover the most designable connections capable of spanning the two architectures. The resulting protein, DFP1 (Due Ferri Porphyrin), bound the two cofactors in the expected manner. The crystal structure of fully reconstituted DFP1 was also in excellent agreement with the design, and it showed the ZnP cofactor bound over 12 Å from the dimetal center. Next, a substrate-binding cleft leading to the diiron center was introduced into DFP1. The resulting protein acts as an allosterically modulated phenol oxidase. Its Michaelis–Menten parameters were strongly affected by the binding of ZnP, resulting in a fourfold tighter Km and a 7-fold decrease in kcat. These studies establish the feasibility of designing allosterically regulated catalytic proteins, entirely from scratch.

Significance In contrast to conventional electronics, spintronics devices exploit the electron spin as an additional degree of freedom. The chirality-induced spin selectivity (CISS) effect, in which chiral molecules act as spin filters in electron transport, provides a pathway to control spins in molecules. We describe an approach that integrates both spin-polarizing and spin-propagating functionality into organic structures that feature low charge transport resistances. Binding chiral ligands to molecular wires controls polarized spin handedness, regulates spin currents, generates large NIR rotational strengths, and provides a mechanism to flip the favored spin orientation for spin transmission through chiral organic molecules. This work points the way to materials that provide both high spin selectivity and large-magnitude spin currents via the CISS mechanism.

Understanding factors that underpin the signs and magnitudes of electron spin-spin couplings in biradicaloids, especially those that are integrated into highly delocalized electronic structures, promises to inform the design of molecular spintronic systems. Using steady-state and variable temperature electron paramagnetic resonance (EPR) spectroscopy, we examine spin dynamics in symmetric, strongly π-conjugated bis[(porphinato)copper] (bis[PCu]) systems and probe the roles played by atom-specific macrocycle spin density, porphyrin-to-porphyrin linkage topology, and orbital symmetry on the magnitudes of electronic spin-spin couplings over substantial Cu-Cu distances. These studies examine the following: (i) meso-to-meso-linked bis[PCu] systems having oligoyne spacers, (ii) meso-to-meso-bridged bis[PCu] arrays in which the PCu centers are separated by a single ethynyl unit or multiple 5,15-diethynyl(porphinato)zinc(II) units, and (iii) the corresponding β-to-β-bridged bis[PCu] structures. EPR data show that, for β-to-β-bridged systems and meso-to-meso-linked bis[PCu] structures having oligoyne spacers, a through σ-bond coupling mechanism controls the average exchange interaction (Javg). In contrast, PCu centers separated by a single ethynyl or multiple 5,15-diethynyl(porphinato)zinc(II) units display a phenomenological decay of ln[Javg] versus Cu-Cu σ-bond separation number of ∼0.115 per bond, half as large as for these other compositions, congruent with the importance of π-mediated spin-spin coupling. These disparities derive from effects that trace their origin to the nature of the macrocycle-macrocycle linkage topology and the relative energy of the Cu dx2-y2 singly occupied molecular orbital within the frontier orbital manifold of these electronically delocalized structures. This work provides insight into approaches to tune the extent of spin exchange interactions and distance-dependent electronic spin-spin coupling magnitudes in rigid, highly conjugated biradicaloids.

Significance The main hurdle that prevents earth-abundant iron-based complexes from replacing environmentally unfriendly and expensive heavy metal [e.g., Ru(II), Os(II), Ir(III)] complexes in solar-energy conversion applications is the typical ultrashort (femtosecond timescale) charge-transfer state lifetime of Fe(II) chromophores. We provide a design roadmap to a generation of efficient iron-based photosensitizers and present an Fe(II) complex archetype, FeNHCPZn, which features a profoundly extended metal-to-ligand charge-transfer (3MLCT) lifetime and a large transition-dipole moment difference between its ground and metal-to-ligand charge-transfer states. This supermolecular design promotes superior visible photon harvesting over classic metal complexes while assuring a triplet excited-state oxidation potential appropriate for charge injection into the conduction bands of common semiconductor electrode materials, highlighting its photosensitizing utility in dye-sensitized solar-cell architectures., Exploiting earth-abundant iron-based metal complexes as high-performance photosensitizers demands long-lived electronically excited metal-to-ligand charge-transfer (MLCT) states, but these species suffer typically from femtosecond timescale charge-transfer (CT)-state quenching by low-lying nonreactive metal-centered (MC) states. Here, we engineer supermolecular Fe(II) chromophores based on the bis(tridentate-ligand)metal(II)-ethyne-(porphinato)zinc(II) conjugated framework, previously shown to give rise to highly delocalized low-lying 3MLCT states for other Group VIII metal (Ru, Os) complexes. Electronic spectral, potentiometric, and ultrafast pump–probe transient dynamical data demonstrate that a combination of a strong σ-donating tridentate ligand and a (porphinato)zinc(II) moiety with low-lying π*-energy levels, sufficiently destabilize MC states and stabilize supermolecular MLCT states to realize Fe(II) complexes that express 3MLCT state photophysics reminiscent of their heavy-metal analogs. The resulting Fe(II) chromophore archetype, FeNHCPZn, features a highly polarized CT state having a profoundly extended 3MLCT lifetime (160 ps), 3MLCT phosphorescence, and ambient environment stability. Density functional and domain-based local pair natural orbital coupled cluster [DLPNO-CCSD(T)] theory reveal triplet-state wavefunction spatial distributions consistent with electronic spectroscopic and excited-state dynamical data, further underscoring the dramatic Fe metal-to-extended ligand CT character of electronically excited FeNHCPZn. This design further prompts intense panchromatic absorptivity via redistributing high-energy absorptive oscillator strength throughout the visible spectral domain, while maintaining a substantial excited-state oxidation potential for wide-ranging photochemistry––highlighted by the ability of FeNHCPZn to photoinject charges into a SnO2/FTO electrode in a dye-sensitized solar cell (DSSC) architecture. Concepts enumerated herein afford opportunities for replacing traditional rare-metal–based emitters for solar-energy conversion and photoluminescence applications.

A new series of strongly coupled oscillators based upon (porphinato)Pd, (porphinato)Pt, and bis(terpyridyl)ruthenium(II) building blocks is described. These RuPPd, RuPPt, RuPPdRu, and RuPPtRu chromophores feature bis(terpyridyl)Ru(II) moieties connected to the (porphinato)metal unit via an ethyne linker that bridges the 4'-terpyridyl and porphyrin macrocycle meso-carbon positions. Pump-probe transient optical data demonstrate sub-picosecond excited singlet-to-triplet-state relaxation. The relaxed lowest-energy triplet (T1) excited states of these chromophores feature absorption manifolds that span the 800-1200 nm spectral region, microsecond triplet-state lifetimes, and large absorptive extinction coefficients [e(T1 → Tn) > 4 × 104 M-1 cm-1]. Dynamic hyperpolarizability (βλ) values were determined from hyper-Rayleigh light scattering (HRS) measurements carried out at several incident irradiation wavelengths over the 800-1500 nm spectral region. Relative to benchmark RuPZn and RuPZnRu chromophores which showed large βHRS values over the 1200-1600 nm range, RuPPd, RuPPt, RuPPdRu, and RuPPtRu displayed large βHRS values over the 850-1200 nm region. Generalized Thomas-Kuhn sum (TKS) rules and experimental hyperpolarizability values were utilized to determine excited state-to-excited state transition dipole terms from experimental electronic absorption data and thus assessed frequency-dependent βλ values, including two- and three-level contributions for both βzzz and βxzx tensor components to the RuPPd, RuPPt, RuPPdRu, and RuPPtRu hyperpolarizability spectra. These analyses qualitatively rationalize how the βzzz and βxzx tensor elements influence the observed irradiation wavelength-dependent hyperpolarizability magnitudes. The TKS analysis suggests that supermolecules related to RuPPd, RuPPt, RuPPdRu, and RuPPtRu will likely feature intricate dependences of experimentally determined βHRS values as a function of irradiation wavelength that derive from substantial singlet-triplet mixing, and complex interactions among multiple different β tensor components that modulate the long wavelength regime of the nonlinear optical response.

High quantum yield NIR fluorophores are rare. Factors that drive low emission quantum yields at long wavelength include the facts that radiative rate constants increase proportional to the cube of the emission energy, while nonradiative rate constants increase in an approximately exponentially with decreasing S0–S1 energy gaps (in accordance with the energy gap law). This work demonstrates how the proquinoidal BTD building blocks can be utilized to minimize the extent of excited-state structural relaxation relative to the ground-state conformation in highly conjugated porphyrin oligomers, and shows that 4-ethynylbenzo[c][1,2,5]thiadiazole (E-BTD) units that terminate meso-to-meso ethyne-bridged (porphinato)zinc (PZnn) arrays, and 4,7-diethynylbenzo[c][1,2,5]thiadiazole (E-BTD-E) spacers that are integrated into the backbone of these compositions, elucidate new classes of impressive NIR fluorophores. We report the syntheses, electronic structural properties, and emissive characteristics of neoteric PZn-(BTD-PZn)n, PZn2-(BTD-PZn2)n, and BTD-PZnn-BTD fluorophores. Absolute fluorescence quantum yield (ϕf) measurements, acquired using a calibrated integrating-sphere-based measurement system, demonstrate that these supermolecules display extraordinary ϕf values that range from 10–25% in THF solvent, and between 28–36% in toluene solvent over the 700–900 nm window of the NIR. These studies underscore how the regulation of proquinoidal conjugation motifs can be exploited to drive excited-state dynamical properties important for high quantum yield long-wavelength fluorescence emission., Incorporation of proquinoidal BTD building blocks into conjugated porphyrin oligomers minimizes the extent of excited-state structural relaxation relative to the ground-state conformation, elucidating new classes of impressive NIR fluorophores.

Purpose A nanoscintillator-based fiber-optic dosimeter (nanoFOD) was developed to measure real-time dose rate during high-dose-rate (HDR) brachytherapy. A trial was designed to prospectively test clinical feasibility in gynecologic implants. Methods and Materials A clinical trial enrolled women undergoing vaginal cylinder HDR brachytherapy. The nanoFOD was fixed to the cylinder alongside two thermoluminescent dosimeters (TLDs). Treatment was delivered and real-time dose rates captured by the nanoFOD. The nanoFOD and TLD positions were identified in CT images and used to extract the treatment planning system (TPS) calculated dose. The nanoFOD and TLD cumulative doses were compared with the TPS. Results Nine women were enrolled for 30 fractions, and real-time data were available in 27 treatments. The median ratio of nanoFOD/TPS dose was 1.00 (IQR 0.94–1.02), with a TLD/TPS ratio of 1.01 (IQR 0.98–1.04). Of the nanoFOD dose measurements, 63% were within 5% of the TPS, 26% between 5 and 10% of the TPS, and the remaining 11% between 10 and 20% of the TPS dose. Of the TLD measurements, 70% were within 5% of the TPS, 22% between 5 and 10% of the TPS, and 7% between 10 and 20% of the TPS dose. Conclusions Real-time dose-rate measurements during HDR brachytherapy were feasible using the nanoFOD and cumulative dose per fraction showed reasonable agreement to TLD and TPS doses. Additional studies to determine dose thresholds that would yield a low false alarm rate and ongoing device development efforts to improve localization of the scintillator in CT images are needed before this detector should be used to inform clinical decisions.

Gauging free carrier generation (FCG) in optically excited, charge-neutral single-walled carbon nanotubes (SWNTs) has important implications for SWNT-based optoelectronics that rely upon conversion of photons to electrical current. Earlier investigations have largely provided only qualitative insights into optically triggered SWNT FCG, due to the heterogeneous nature of commonly interrogated SWNT samples and the lack of direct, unambiguous spectroscopic signatures that could be used to quantify charges. Here, employing ultrafast pump–probe spectroscopy in conjunction with chirality-enriched, length-sorted, ionic-polymer-wrapped SWNTs, we develop a straightforward approach for quantitatively evaluating the extent of optically driven FCG in SWNTs. Owing to the previously identified trion transient absorptive hallmark (Tr+11 → Tr+nm) and the rapid nature of trion formation dynamics ( ns), we correlate FCG with trion formation dynamics. Experiment...

Summary Electron-transport-layer-free (ETL-free) device architectures are promising designs for perovskite photovoltaics because they offer simpler configurations, low cost, and convenience for versatile optoelectronics. However, the development of ETL-free photovoltaics is hindered by their low performance. Herein, we reveal that a low electron-injection rate at the ETL-free interface is responsible for the performance loss. Moreover, we demonstrate that improving carrier lifetimes in the perovskite films can remedy the poor carrier extraction at interfaces, enabling carrier collection efficiency in ETL-free photovoltaics to approach that in ETL-containing devices. Using perovskite films with microsecond carrier lifetimes, we obtained ETL-free devices with a power conversion efficiency (PCE) of 19.5%, nearly eliminated hysteresis, and good stability. Such a PCE value is comparable to that (20.7%) of the analogous ETL-containing photovoltaics. These results offer opportunities for ETL-free architecture designs in the perovskite photovoltaics family. More importantly, this research provides a general approach to improving the performance of photovoltaics with low-injection-rate interfaces.

De novo protein design offers the opportunity to test our understanding of how metalloproteins perform difficult transformations. Attaining high-resolution structural information is critical to understanding how such designs function. There have been many successes in the design of porphyrin-binding proteins; however, crystallographic characterization has been elusive, limiting what can be learned from such studies as well as the extension to new functions. Moreover, formation of highly oxidizing high-valent intermediates poses design challenges that have not been previously implemented: (1) purposeful design of substrate/oxidant access to the binding site and (2) limiting deleterious oxidation of the protein scaffold. Here we report the first crystallographically characterized porphyrin-binding protein that was programmed to not only bind a synthetic Mn-porphyrin but also maintain binding site access to form high-valent oxidation states. We explicitly designed a binding site with accessibility to dioxygen units in the open coordination site of the Mn center. In solution, the protein is capable of accessing a high-valent Mn(V)-oxo species which can transfer an O atom to a thioether substrate. The crystallographic structure is within 0.6 A of the design and indeed contained an aquo ligand with a second water molecule stabilized by hydrogen bonding to a Gln side chain in the active site, offering a structural explanation for the observed reactivity.

The rapid growth of electronic waste must be curtailed to prevent accumulation of environmentally and biologically toxic materials, which are essential to traditional electronics. The recent proliferation of transient electronics has focused predominantly on biocompatibility, and studies reporting material recapture have only demonstrated reuse of conducting materials. Meanwhile, the ideal solution to the electronic waste epidemic-recapture and reuse of all materials-has been largely neglected. Here we show complete recyclability of all materials in printed, all-carbon electronics using paper substrates, semiconducting carbon nanotubes, conducting graphene, and insulating crystalline nanocellulose. The addition of mobile ions to the dielectric produced significant improvements in switching speed, subthreshold swing, and among the highest on-current for printed transistors. These devices evinced superlative stability over 6 months, after which they are shown to be controllably decomposed for complete recycling of materials and re-printing of devices with similar performance to baseline devices. The printing of all-carbon, recyclable electronics presents a new path toward green electronics with potential to mitigate the environmental impact of electronic waste. We anticipate all-carbon, recyclable electronics to be a watershed, facilitating internet-of-everything applications, such as ubiquitous sensors for continuous monitoring of diseases or environmental conditions, while preserving carbon neutrality in the device lifecycle., 16 pages, 3 figures

A series of new π-stacked compounds, 1,8-bis(2′,5′-dimethoxybenzene-1′-yl)naphthalene (1), 1,4-bis(8′-(2″,5″-dimethoxybenzene-1″-yl)naphthalen-1′-yl)benzene (2), and 1,8-bis(4′-(8″-(2‴,5‴-dimethoxy...

Photoluminescent sp3 defect states introduced to single wall carbon nanotubes (SWCNTs) through low-level covalent functionalization create new photophysical behaviors and functionality as a result of defect sites acting as exciton traps. Evaluation of relaxation dynamics in varying dielectric environments can aid in advancing a more complete description of defect-state relaxation pathways and electronic structure. Here, we exploit helical wrapping polymers as a route to suspending (6,5) SWCNTs covalently functionalized with 4-methoxybenzene in solvent systems including H2O, D2O, methanol, dimethylformamide, tetrahydrofuran, and toluene, spanning a range of dielectric constants from 80 to 3. Defect-state photoluminescence decays were measured as a function of emission wavelength and solvent environment. Emission decays are biexponential, with short lifetime components on the order of 65 ps and long components ranging from around 100 to 350 ps. Both short and long decay components increase as emission wavel...

The trion, a three-body charge-exciton bound state, offers unique opportunities to simultaneously manipulate charge, spin, and excitation in one-dimensional single-walled carbon nanotubes (SWNTs) at room temperature. Effective exploitation of trion quasi-particles requires fundamental insight into their creation and decay dynamics. Such knowledge, however, remains elusive for SWNT trion states, due to the electronic and morphological heterogeneity of commonly interrogated SWNT samples, and the fact that transient spectroscopic signals uniquely associated with the trion state have not been identified. Here, we prepare length-sorted SWNTs and precisely control charge-carrier-doping densities to determine trion dynamics using femtosecond pump–probe spectroscopy. Identification of the trion transient absorptive hallmark enables us to demonstrate that trions (i) derive from a precursor excitonic state, (ii) are produced via migration of excitons to stationary hole-polaron sites, and (iii) decay in a first-order manner. Importantly, under appropriate carrier-doping densities, exciton-to-trion conversion in SWNTs can approach 100% at ambient temperature. Our findings open up possibilities for exploiting trions in SWNT optoelectronics, ranging from photovoltaics and photodetectors to spintronics.

We report the synthesis and excited-state dynamics of a bis[p-ethynyldithiobenzoato]Pd(II)-bridged bis[(porphinato) zinc(II)] complex (PZn–Pd(edtb)2–PZn) that exhibits unusual solvent dielectric (e)-dependent excited-state relaxation behavior. In nonpolar toluene solvent, PZn–Pd(edtb)2–PZn manifests an ultrafast S1 → T1 intersystem crossing time constant (τISC ≈ 2 ps), a broad, high-oscillator strength T1 → Tn transient absorption manifold (λmax(T1 → Tn) = 940 nm), and a near unity triplet-state formation quantum yield (ΦT ≈ 1; τT = 2.2 μs). In contrast, in moderately polar solvents (e.g., dichloromethane (DCM) or THF), the S1 → T1 intersystem crossing quantum yield is significantly suppressed (ΦT ≈ 0.2; τF ≈ 60 ps in DCM). Comparative femtosecond transient absorption studies in DCM and mixed DCM/toluene solvent systems reveal a new low-energy stimulated emission signal, the λmaxem of which is highly sensitive to solvent polarity. The lack of spectral signatures for radical species, and the emergence of intense stimulated emission indicate an additional low energy electronically excited-state (S*), populated via S1-state relaxation, that also possesses substantial singlet character. As solvent polarity is progressively increased, the energy of S* progressively decreases, eventually becoming lower than the S1 state and providing an excited-state relaxation channel that bypasses T1 state formation. These data show that the nature of the PZn–Pd(edtb)2–PZn excited-state dynamics is strongly influenced by the solvent dielectric, and that this Pd(II)-based linker motif offers new opportunities to engineer excited-state spin distributions and lifetimes in strongly conjugated chromophore assemblies.

Elucidating structure–function relationships that determine the photophysics of nanomaterials that upconvert high-power, near-infrared (NIR) excitation to shorter wavelength NIR, visible, and UV emission requires both compositional characterization and experimental designs that rigorously define laser excitation conditions and the manner in which emitted photons are collected. Presented herein are laser power-dependent, total-emitted radiant flux (watts), and absolute quantum yield measurements of homogeneous, solution-phase 28 nm [NaYF4; Yb (15%), Er (2%)] upconversion nanocrystals (UCNCs) determined using a multidetector integrating sphere spectroscopy system. These studies compare for the first time quantitative total radiant flux and absolute quantum yield measurements of UCNCs determined as a function of laser power density for both 970 nm continuous-wave (CW) and 976 nm pulsed Ti-sapphire (140 fs pulse width, 80 MHz) laser excitation. This study illustrates that at intensities in the range 35–225 W/...

If we truly understand proteins, we should be able to design functional proteins purposefully from scratch. While the de novo design of proteins has seen many successes1–11, no small molecule ligand- or organic cofactor-binding protein has been designed entirely from first principles to achieve i) a unique structure and ii) a predetermined binding-site geometry with sub-Å accuracy. Such achievements are prerequisites for the design of proteins that control and enable complex reaction trajectories, where the relative placements of cofactors, substrates, and protein side chains must be established within the length scale of a chemical bond. Here, we develop and test a strategy for design of small molecule-binding proteins, based on the concept that the entire protein contributes to establishing the binding geometry of a ligand12–15. Hence, what are traditionally considered as separate sectors – the hydrophobic core and ligand-binding site – we treat as an inseparable unit. We utilize flexible backbone sequence design of a parametrically defined protein template to simultaneously pack the protein interior both proximal to and remote from the ligand-binding site. Thus, tight interdigitation of core side chains quite removed from the binding site structurally restrains the first- and second-shell packing around the ligand. We apply this principle to the decades-old problem of structural non-uniqueness in de novo-designed heme-binding proteins16. We designed a novel protein, PS1, which binds a highly electron-deficient, non-natural porphyrin at temperatures up to 100 °C. The high-resolution structure of holo-PS1 is in sub-Å agreement with the design. The structure of apo-PS1 retains the remote core packing of the holo, predisposing a flexible binding region for the desired ligand-binding geometry. Our results reveal the unification of core packing and binding site definition as an essential principle of ligand-binding protein design.

Spin and conformational dynamics in symmetric alkyne-bridged multi[copper(II) porphyrin] structures have been studied in toluene solution at variable temperature using steady-state electron paramagnetic resonance (EPR) spectroscopy. Comparison of the dimer EPR spectra to those of Cu porphyrin monomers shows evidence of an isotropic exchange interaction (Javg) in these biradicaloid structures, manifested by a significant line broadening in the dimer spectra. The extent line broadening depends on molecular structure and temperature, suggesting Javg is modulated by conformational dynamics that impact the torsional angle distribution between the porphyrin–porphyrin least-squares planes. Computational simulation of the experimental EPR spectra, using a developed algorithm for J modulation in flexible organic biradicals, supports this hypothesis. Comparison of ethyne and butadiyne alkyne bridges reveals remarkable sensitivity to orbital interactions between the spacer and the metal, reflected in measurements of...

Challenging photochemistry demands high-potential visible-light-absorbing photo-oxidants. We report (i) a highly electron-deficient Ru(II) complex (eDef-Rutpy) bearing an E1/20/+ potential more than 300 mV more positive than that of any established Ru(II) bis(terpyridyl) derivative, and (ii) an ethyne-bridged eDef-Rutpy−(porphinato)Zn(II) (eDef-RuPZn) supermolecule that affords both panchromatic UV–vis spectral domain absorptivity and a high E1/20/+ potential, comparable to that of Ce(NH4)2(NO3)6 [E1/2(Ce3+/4+) = 1.61 V vs NHE], a strong and versatile ground-state oxidant commonly used in organic functional group transformations. eDef-RuPZn exhibits ∼8-fold greater absorptive oscillator strength over the 380–700 nm range relative to conventional Ru(II) polypyridyl complexes, and impressive excited-state reduction potentials (1E–/* = 1.59 V; 3E–/* = 1.26 V). eDef-RuPZn manifests electronically excited singlet and triplet charge-transfer state lifetimes more than 2 orders of magnitude longer than those typi...

Compared to conventional core-shell structures, core-shell free nanoparticles with multiple functionalities offer several advantages such as minimal synthetic complexity and low production cost. In this paper, we present the synthesis and characterization of Nd3+ doped Na(Gd0.5Lu0.5)F4 as a core-shell free nanoparticle system with three functionalities. Nanocrystals with 20 nm diameter, high crystallinity and a narrow particle size distributions were synthesized by the solvothermal method and characterized by various analytical techniques to understand their phase and morphology. Fluorescence characteristics under near infrared (NIR) excitation at 808 nm as well as X-ray excitation were studied to explore their potential in NIR optical and X-ray imaging. At 1.0 mol% Nd concentration, we observed a quantum yield of 25% at 1064 nm emission with 13 W/cm2 excitation power density which is sufficiently enough for imaging applications. Under 130 kVp (5 mA) power of X-ray excitation, Nd3+ doped Na(Gd0.5Lu0.5)F4 shows the characteristic emission bands of Gd3+ and Nd3+ with the strongest emission peak at 1064 nm due to Nd3+. Furthermore, magnetization measurements show that the nanocrystals are paramagnetic in nature with a calculated magnetic moment per particle of ~570 μB at 2T. These preliminary results support the suitability of the present nanophosphor as a multimodal contrast agent with three imaging features viz. optical, magnetic and X-ray.

Perovskite photovoltaics have attracted remarkable attention recently due to their exceptional power conversion efficiencies (PCE). State-of-the-art perovskite absorbers typically require thermal annealing steps for high film quality. However, the annealing process adds cost and reduces yield for device fabrication and may also hinder application in tandem photovoltaics and flexible/ultra-low-cost optoelectronics. Herein, we report an additive-based room-temperature process for realizing high-quality methylammonium lead iodide films with micron-sized grains (>2 μm) and microsecond-range carrier lifetimes (τ1 = 931.94 ± 89.43 ns; τ2 = 320.41 ± 43.69 ns). Solar cells employing such films demonstrate 18.22% PCE with improved current–voltage hysteresis and stability without encapsulation. Further, we reveal that room-temperature-processed perovskite film grain size strongly depends on the precursor aggregate size in the film-deposition solution and that additive-based tuning of aggregate properties enables enlarging grains to the micron scale. These results offer a new pathway for more versatile, cost-effective perovskite processing.

While the influence of proquinoidal character upon the linear absorption spectrum of low optical bandgap π-conjugated polymers and molecules is well understood, its impact upon excited-state relaxation pathways and dynamics remains obscure. We report the syntheses, electronic structural properties, and excited-state dynamics of a series of model highly conjugated near-infrared (NIR)-absorbing chromophores based on a (porphinato)metal(II)-proquinoidal spacer-(porphinato)metal(II) (PM-Sp-PM) structural motif. A combination of excited-state dynamical studies and time-dependent density functional theory calculations: (i) points to the cardinal role that excited-state configuration interaction (CI) plays in determining the magnitudes of S1 → S0 radiative (kr), S1 → T1 intersystem crossing (kISC), and S1 → S0 internal conversion (kIC) rate constants in these PM-Sp-PM chromophores, and (ii) suggests that a primary determinant of CI magnitude derives from the energetic alignment of the PM and Sp fragment LUMOs (ΔEL). These insights not only enable steering of excited-state relaxation dynamics of high oscillator strength NIR absorbers to realize either substantial fluorescence or long-lived triplets (τT1 > μs) generated at unit quantum yield (ΦISC = 100%), but also crafting of those having counter-intuitive properties: for example, while (porphinato)platinum compounds are well known to generate non-emissive triplet states (ΦISC = 100%) upon optical excitation at ambient temperature, diminishing the extent of excited-state CI in these systems realizes long-wavelength absorbing heavy-metal fluorophores. This work highlights approaches to: (i) modulate low-lying singlet excited-state lifetime over the picosecond-to-nanosecond time domain, (ii) achieve NIR fluorescence with quantum yields up to 25%, (iii) tune the magnitude of S1–T1 ISC rate constant from 109 to 1012 s−1 and (iv) realize T1-state lifetimes that range from ∼0.1 to several μs, for these model PM-Sp-PM chromophores, and renders new insights to evolve bespoke photophysical properties for low optical bandgap π-conjugated polymers and molecules based on proquinoidal conjugation motifs.

Octopolar D2-symmetric chromophores, based on the MPZnM supermolecular motif in which (porphinato)zinc(II) (PZn) and ruthenium(II) polypyridyl (M) structural units are connected via ethyne linkages, were synthesized. These structures take advantage of electron-rich meso-arylporphyrin or electron-poor meso-(perfluoroalkyl)porphyrin macrocycles, unsubstituted terpyridyl and 4′-pyrrolidinyl-2,2′;6′,2″-terpyridyl ligands, and modulation of metal(II) polypyridyl-to-(porphinato)zinc connectivity, to probe how electronic and geometric factors impact the measured hyperpolarizability. Transient absorption spectra obtained at early time delays (tdelay < 400 fs) demonstrate fast excited-state relaxation, and formation of a highly polarized T1 excited state; the T1 states of these chromophores display expansive, intense T1 → Tn absorption manifolds that dominate the 800–1200 nm region of the NIR, long (μs) triplet-state lifetimes, and unusually large NIR excited absorptive extinction coefficients [ε(T1 → Tn) ∼ 105 M–1 cm–1]. Dynamic hyperpolarizability (βλ) values were determined from hyper-Rayleigh light scattering (HRS) measurements, carried out at multiple incident irradiation wavelengths spanning the 800–1500 nm spectral domain. The measured βHRS value (4600 ± 1200 × 10–30 esu) for one of these complexes, RuPZnRu, is the largest yet reported for any chromophore at a 1500 nm irradiation wavelength, highlighting that appropriate engineering of strong electronic coupling between multiple charge-transfer oscillators provides a critical design strategy to realize octopolar NLO chromophores exhibiting large βHRS values at telecom-relevant wavelengths. Generalized Thomas–Kuhn sum (TKS) rules were utilized to compute the effective excited-state-to-excited-state transition dipole moments from experimental linear-absorption spectra; these data were then utilized to compute hyperpolarizabilities as a function of frequency, that include two- and three-state contributions for both βzzz and βxzx tensor components to the RuPZnRu hyperpolarizability spectrum. This analysis predicts that the βzzz and βxzx tensor contributions to the RuPZnRu hyperpolarizability spectrum maximize near 1550 nm, in agreement with experimental data. The TKS analysis suggests that relative to analogous dipolar chromophores, octopolar supermolecules will be likely characterized by more intricate dependences of the measured hyperpolarizability upon irradiation wavelength due to the interactions among multiple different β tensor components., Coupling of multiple charge-transfer oscillators generates D2-symmetric octopolar NLO chromophores that exhibit large βHRS values at telecom-relevant wavelengths.

The direction of electron flow in molecular optoelectronic devices is dictated by charge transfer between a molecular excited state and an underlying conductor or semiconductor. For those devices, controlling the direction and reversibility of electron flow is a major challenge. We describe here a single-molecule photodiode. It is based on an internally conjugated, bichromophoric dyad with chemically linked (porphyrinato)zinc(II) and bis(terpyridyl)ruthenium(II) groups. On nanocrystalline, degenerately doped indium tin oxide electrodes, the dyad exhibits distinct frequency-dependent, charge-transfer characters. Variations in the light source between red-light (∼1.9 eV) and blue-light (∼2.7 eV) excitation for the integrated photodiode result in switching of photocurrents between cathodic and anodic. The origin of the excitation frequency-dependent photocurrents lies in the electronic structure of the chromophore excited states, as shown by the results of theoretical calculations, laser flash photolysis, and steady-state spectrophotometric measurements.

Efficient photosynthetic energy conversion requires quantitative, light-driven formation of high-energy, charge-separated states. However, energies of high-lying excited states are rarely extracted, in part because the congested density of states in the excited-state manifold leads to rapid deactivation. Conventional photosystem designs promote electron transfer (ET) by polarizing excited donor electron density toward the acceptor (“one-way” ET), a form of positive design. Curiously, negative design strategies that explicitly avoid unwanted side reactions have been underexplored. We report here that electronic polarization of a molecular chromophore can be used as both a positive and negative design element in a light-driven reaction. Intriguingly, prudent engineering of polarized excited states can steer a “U-turn” ET—where the excited electron density of the donor is initially pushed away from the acceptor—to outcompete a conventional one-way ET scheme. We directly compare one-way vs. U-turn ET strategies via a linked donor–acceptor (DA) assembly in which selective optical excitation produces donor excited states polarized either toward or away from the acceptor. Ultrafast spectroscopy of DA pinpoints the importance of realizing donor singlet and triplet excited states that have opposite electronic polarizations to shut down intersystem crossing. These results demonstrate that oppositely polarized electronically excited states can be employed to steer photoexcited states toward useful, high-energy products by routing these excited states away from states that are photosynthetic dead ends.

A recently proposed oxidative damage protection mechanism in proteins relies on hole hopping escape routes formed by redox-active amino acids. We present a computational tool to identify the dominant charge hopping pathways through these residues based on the mean residence times of the transferring charge along these hopping pathways. The residence times are estimated by combining a kinetic model with well-known rate expressions for the charge-transfer steps in the pathways. We identify the most rapid hole hopping escape routes in cytochrome P450 monooxygenase, cytochrome c peroxidase, and benzylsuccinate synthase (BSS). This theoretical analysis supports the existence of hole hopping chains as a mechanism capable of providing hole escape from protein catalytic sites on biologically relevant timescales. Furthermore, we find that pathways involving the [4Fe4S] cluster as the terminal hole acceptor in BSS are accessible on the millisecond timescale, suggesting a potential protective role of redox-active cofactors for preventing protein oxidative damage.

Many biochemical processes, such as charge hopping or protein folding, can be described by an average timescale to reach a final state, starting from an initial state. Here, we provide a pedagogical treatment of the mean first-passage time (MFPT) of a physical process, which depends on the number of intervening states between the initial state and the target state. Our aim in this tutorial review is to provide a clear development of the mean first-passage time formalism and to show some of its practical utility. The MFPT treatment can provide a useful link between microscopic rates and the average timescales often probed by experiment.

We provide a direct measure of the change in effective dielectric constant (ε(S)) within a protein matrix after a photoinduced electron transfer (ET) reaction. A linked donor-bridge-acceptor molecule, PZn-Ph-NDI, consisting of a (porphinato)Zn donor (PZn), a phenyl bridge (Ph), and a naphthalene diimide acceptor (NDI), is shown to be a "meter" to indicate protein dielectric environment. We calibrated PZn-Ph-NDI ET dynamics as a function of solvent dielectric, and computationally de novo designed a protein SCPZnI3 to bind PZn-Ph-NDI in its interior. Mapping the protein ET dynamics onto the calibrated ET catalogue shows that SCPZnI3 undergoes a switch in the effective dielectric constant following photoinduced ET, from ε(S) ≈ 8 to ε(S) ≈ 3.

Photoluminescent sp

Realizing chromophores that simultaneously possess substantial near-infrared (NIR) absorptivity and long-lived, high-yield triplet excited states is vital for many optoelectronic applications, such as optical power limiting and triplet–triplet annihilation photon upconversion (TTA-UC). However, the energy gap law ensures such chromophores are rare, and molecular engineering of absorbers having such properties has proven challenging. Here, we present a versatile methodology to tackle this design issue by exploiting the ethyne-bridged (polypyridyl)metal(II) (M; M = Ru, Os)-(porphinato)metal(II) (PM′; M′ = Zn, Pt, Pd) molecular architecture (M-(PM′)n-M), wherein high-oscillator-strength NIR absorptivity up to 850 nm, near-unity intersystem crossing (ISC) quantum yields (ΦISC), and triplet excited-state (T1) lifetimes on the microseconds time scale are simultaneously realized. By varying the extent to which the atomic coefficients of heavy metal d orbitals contribute to the one-electron excitation configurati...

In this paper, we report a detailed computational and experimental investigation of the structural, electronic and dynamic properties of undoped and Er3+-doped Y2O2S phosphors by using computational crystal field (CF) calculations and electronic density of states by density functional theory (DFT), combined with optical measurements including excitation spectra, emission spectra from X-ray, ultraviolet and near infrared (NIR) excitations, and quantum yield determination under ultraviolet and NIR excitations. Emission decays and quantum yields of the visible and NIR bands were measured for different Er3+ doping concentrations in the Er3+-doped Y2O2S phosphors. Results show that green (550 nm) and red (667 nm) emission intensity and the respective ratio of these emission intensities depend on both the excitation wavelength and the Er3+ doping concentration. Although the total emission efficiency does not appreciably depend on the excitation wavelength, the excitation wavelength that provided the highest efficiency was found to be 250 nm in these Er3+-doped Y2O2S phosphors with both 1% and 10% Er doping concentrations.

A design strategy for (porphinato)zinc-based fluorophores that possess large near infrared fluorescence quantum yields is described. These fluorophores are based on a (5,15-diethynylporphinato)zinc(II) framework and feature symmetric donor or acceptor units appended at the meso-ethynyl positions via benzo[c][1,2,5]thiadiazole moieties. These (5,15-bis(benzo[c][1′,2′,5′]thiadiazol-4′-ylethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (4), (5,15-bis[4′-(N,N-dihexylamino) benzo[c][1′,2′,5′]thiadiazol-7′-ylethynyl]-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (5), (5,15-bis([7′-(4″-n-dodecyloxyphenylethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (6), (5,15-bis([7′-([7″-(4″ ′-n-dodecyloxyphenyl)benzo[c][1″,2″,5″]thiadiazol-4″-yl]ethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (7), 5,15-bis ([7′-(4″-N,N-dihexylaminophenylethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (8), and (5,15-bis([7′-(4″-N,N-dihexylaminophenylethenyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (9) chromophores possess red-shifted absorption and emission bands that range between 650 and 750 nm that bear distinct similarities to those of the chlorophylls and structurally related molecules. Interestingly, the measured radiative decay rate constants for these emitters track with the integrated oscillator strengths of their respective x-polarized Q-band absorptions, and thus define an unusual family of high quantum yield near infrared fluorophores in which emission intensity is governed by a simple Strickler–Berg dependence.

Motivated by the goal of developing a fully biodegradable optical contrast agent with translational clinical potential, a nanoparticle delivery vehicle was generated from the self-assembly of poly(ethylene-glycol)-block-poly(trimethylene carbonate-co-caprolactone) (PEG-b-TCL) copolymers. Cryogenic transmission electron microscopy verified that PEG-b-TCL-based micelles were formed at low solution temperatures (~ 38 °C). Detailed spectroscopic experiments validated facile loading of large quantities of the high emission dipole strength, tris(porphyrin)-based fluorophore PZn3 within their cores, and the micelles displayed negligible in vitro and in vivo toxicities in model systems. The pharmacokinetics and biodistribution of PZn3-loaded PEG-b-TCL-based micelles injected intravenously were determined via ex vivo near-infrared (NIR) imaging of PZn3 emission in microcapillary tubes containing minute quantities of blood, to establish a novel method for minimally invasive pharmacokinetic monitoring. The in vivo circulatory half-life of the PEG-b-TCL-based micelles was found to be ~19.6 h. Additionally, longitudinal in vivo imaging of orthotopically transplanted breast tumors enabled determination of micelle biodistribution that correlated to ex vivo imaging results, demonstrating accumulation predominantly within the tumors and livers of mice. The PEG-b-TCL-based micelles quickly extravasated within 4T1 orthotopic mammary carcinomas, exhibiting peak accumulation at ~48 h following intravenous tail-vein injection. In summary, PEG-b-TCL-based micelles demonstrated favorable characteristics for further development as in vivo optical contrast agents for minimally invasive imaging of breast tumors.

Compared to conventional core-shell structures, core-shell free nanoparticles with multiple functionalities offer several advantages such as minimal synthetic complexity and low production cost. In this paper, we present the synthesis and characterization of Nd3+ doped Na(Gd0.5Lu0.5)F4 as a core-shell free nanoparticle system with three functionalities. Nanocrystals with 20 nm diameter, high crystallinity and a narrow particle size distributions were synthesized by the solvothermal method and characterized by various analytical techniques to understand their phase and morphology. Fluorescence characteristics under near infrared (NIR) excitation at 808 nm as well as X-ray excitation were studied to explore their potential in NIR optical and X-ray imaging. At 1.0 mol% Nd concentration, we observed a quantum yield of 25% at 1064 nm emission with 13 W/cm2 excitation power density which is sufficiently enough for imaging applications. Under 130 kVp (5 mA) power of X-ray excitation, Nd3+ doped Na(Gd0.5Lu0.5)F4 shows the characteristic emission bands of Gd3+ and Nd3+ with the strongest emission peak at 1064 nm due to Nd3+. Furthermore, magnetization measurements show that the nanocrystals are paramagnetic in nature with a calculated magnetic moment per particle of ~570 μB at 2T. These preliminary results support the suitability of the present nanophosphor as a multimodal contrast agent with three imaging features viz. optical, magnetic and X-ray.

We report the synthesis, transient absorption, FT Raman, resonance Raman, time-resolved resonance Raman, and transient resonance Raman spectra of pseudo-D 2 h symmetric [5,15-bis[(4‘-nitrophenyl)ethynyl]-10,20-diphenylporphinato]copper(II) (I) and electronically asymmetric [5-[4‘-(dimethylamino)phenyl]ethynyl]-15-[(4‘‘-nitrophenyl)ethynyl]-10,20-diphenylporphinato]copper(II) (II), which bears both electron-releasing and electron-withdrawing groups conjugated directly to the porphyrin periphery. The spectroscopic results suggest extensive electronic communication between the 5- and 15-arylethynyl groups and the porphyrin core. Relative to the parent compound, (tetraphenylporphinato)copper(II) (CuTPP), the arylethynyl substituents increase the lifetime of the excited trip-multiplet states. CuTPP, as well as compounds I and II, however, shows similar solvent-dependent dynamics: the trip-multiplet lifetimes are longer in a noncoordinating solvent such as benzene than in a coordinating solvent such as THF. Th...

The influence of electronic symmetry on triplet state delocalization in linear zinc porphyrin oligomers is explored by electron paramagnetic resonance techniques. Using a combination of transient continuous wave and pulse electron nuclear double resonance spectroscopies, it is demonstrated experimentally that complete triplet state delocalization requires the chemical equivalence of all porphyrin units. These results are supported by density functional theory calculations, showing uneven delocalization in a porphyrin dimer in which a terminal ethynyl group renders the two porphyrin units inequivalent. When the conjugation length of the molecule is further increased upon addition of a second terminal ethynyl group that restores the symmetry of the system, the triplet state is again found to be completely delocalized. The observations suggest that electronic symmetry is of greater importance for triplet state delocalization than other frequently invoked factors such as conformational rigidity or fundamental length-scale limitations.

We report the first direct cyclic voltammetric determination of the valence and conduction band energy levels for noncovalently modified (6,5) chirality enriched SWNTs [(6,5) SWNTs] in which an aryleneethynylene polymer monolayer helically wraps the nanotube surface at periodic and constant morphology. Potentiometric properties as well as the steady-state and transient absorption spectroscopic signatures of oxidized (6,5) SWNTs were probed as a function of the electronic structure of the aryleneethynylene polymer that helically wraps the nanotube surface, the solvent dielectric, and nanotube hole polaron concentration. These data: (i) highlight the utility of these polymer-SWNT superstructures in experiments that establish the potentiometric valence and conduction band energy levels of semiconducting carbon nanotubes; (ii) provide a direct measure of the (6,5) SWNT hole polaron delocalization length (2.75 nm); (iii) determine steady-state and transient electronic absorptive spectroscopic signatures that are uniquely associated with the (6,5) SWNT hole polaron state; and (iv) demonstrate that modulation of semiconducting polymer frontier orbital energy levels can drive spectral shifts of SWNT hole polaron transitions as well as regulate SWNT valence and conduction band energies.