Stable Cis Research Articles

Stability of a photosurfactant-laden viscous liquid thread under illumination

This paper investigates the effects of a light-actuated photosurfactant on the canonical problem of the linear stability of a viscous thread surrounded by a dynamically passive fluid. A model consisting of the Navier–Stokes equations and a set of molar concentration equations is presented that capture light-induced switching between two stable surfactant isomer states, trans and cis. These two states display significantly different interfacial properties, allowing for some external control of the stability behaviour of the thread via incident light. Normal modes are used to generate a generalized eigenvalue problem for the growth rate which is solved with a hybrid analytical and numerical method. The results are validated with appropriate analytical solutions of increasing complexity, beginning with a solution to a clean interface, then analytical solutions for one insoluble surfactant, one soluble surfactant and a special case of two photosurfactants with a spatially uniform undisturbed state. Presenting each of these cases allows for a holistic discussion of the effect of surfactants in general on the stability of a liquid thread. Finally, the numerical solutions in the presence of two photosurfactants that display radially non-uniform undisturbed states are presented, and details of the impact of the illumination on the linear stability of the thread are discussed.

Geometry-induced Oligomerization of Fluorine-substituted Phenylazothiazole Photoswitches.

Photoswitches are molecules that can absorb light of specific wavelengths and undergo a reversible transformation between their trans and cis isomeric forms. In phenylazo photoswitches, it is common for the less stable cis (Z) isomer to convert back to the more stable trans (E) isomer either through photochemical or thermal means. In this research, we designed new derivatives of phenylazothiazole (PAT) photoswitches, PAT-Fn, which feature fluorine substituents on their phenyl component. These derivatives can reversibly isomerize under visible light exposure with the enrichment of E and Z isomers at photostationary state (PSS). Surprisingly, we observed an unconventional phenomenon when these PAT-Fn (n ≧2) photoswitches were in their cis isomeric state in the absence of light. Instead of the anticipated transformation from cis to trans isomer, these compounds converted to an oligomeric compound. Our detailed experimental investigation and theoretical calculations, indicated the crucial role of fluorine substituents and the distinctive geometric arrangement of the cis isomer in driving the unexpected oligomerization process originating from the cis isomeric state.

Isomerization dynamics of a novel cis/trans‐only merocyanine

AbstractMerocyanines (MC) usually adopt ring opened zwitterionic structures that are interconvertible with their ring‐closed spiropyran photoisomers. By methylating the phenolate oxygen, and thereby blocking the ring‐closure reaction, a cis/trans‐only MC photoswitch was obtained, yielding a perfect candidate for a detailed examination of the cis/trans isomerization mechanism for this class of compounds. This photoswitch displays outstanding properties including excellent photoreaction quantum yields and photoswitching turnovers. Due to the central polymethine bridge of MC, in principle eight cis (C)/trans/(T) isomers are possible. Density Functional Theory (DFT) calculations revealed the CCT and TTT‐isomers of the studied compound as most stable cis and trans ground state isomers, respectively. UV/vis transient absorption studies combined with conical intersection computations with the complete active space self‐consistent field (CASSCF) method show that both trans/cis‐ and cis/trans‐photoisomerizations are initiated by a rotation of the central doubled bond fragment. A hot ground state species is then formed, which undergoes a second isomerization. Thus, the cis/trans reaction proceeds via a CCT‐CTT‐TTT sequence and the reverse reaction via TTT‐TCT‐CCT.

A Complete Unveiling of the Mechanism and Chirality in Photoisomerization of Arylazopyrazole 3pzH: Combined Electronic Structure Calculations and AIMS Dynamic Simulations.

The arylazopyrazole 3pzH as a novel photoswitch exhibits quantitative switching and high thermal stability. In this work, combined electronic structure calculations and ab initio multiple spawning (AIMS) dynamic simulations were performed to systemically investigate the cis ↔ trans photoisomerization mechanism and the chiral preference after photoexcitation of 3pzH to the first excited singlet state (S1). Unlike most of the azoheteroarene photoswitches reported previously, many twisted and T-shaped cis isomers were found to be stable for 3pzH in the S0 state, owing to the moderate interaction between the hydrogen atom and π electrons of the aromatic ring. Two twisted cis isomers with different chirality ((M)-Z1 and (P)-Z1), the most stable T-shaped cis isomer ((T)-Z2), and the most stable planar trans isomer (E2) were selected as the initial structures to carry out the AIMS nonadiabatic dynamic simulations. Following excitation to the S1 state, all of the cis isomers decayed to conical intersection (CI) regions via the same bicycle pedal mechanism, while the evolution of the trans isomers to their CI regions was achieved via rotation around the N═N bond. More importantly, chiral preferences were found for the twisted cis isomers in the S1 state through the AIMS dynamic simulations due to the steric effect and static electronic repulsion. Notably, chirality was also observed in S1 isomerization starting from the planar E2 isomer because of the dynamic effect. After the nonadiabatic transition to the S0 state, the bicycle pedal mechanism was found to play a crucial role in cis ↔ trans photoisomerization. The simulated photoisomerization productivities were generally consistent with past experimental observations. Our calculations not only uncover the underlying reason for the excellent photoswitching properties of 3pzH but also enrich the knowledge of photoisomerization for azoheteroarene photoswitches, which will surely benefit their rational design.

Coordination of Al(C6F5)3 vs. B(C6F5)3 on group 6 end-on dinitrogen complexes: chemical and structural divergences.

The coordination of the Lewis superacid tris(pentafluorophenyl)alane (AlCF) to phosphine-supported, group 6 bis(dinitrogen) complexes [ML2(N2)2] is explored, with M = Cr, Mo or W and L = dppe (1,2-bis(diphenylphosphino)ethane), depe (1,2-bis(diethylphosphino)ethane), dmpe (1,2-bis(dimethylphosphino)ethane) or 2 × PMe2Ph. Akin to tris(pentafluorophenyl)borane (BCF), AlCF can form 1 : 1 adducts by coordination to one distal nitrogen of general formula trans-[ML2(N2){(μ-η1:η1-N2)Al(C6F5)3}]. The boron and aluminium adducts are structurally similar, showing a comparable level of N2 push-pull activation. A notable exception is a bent (BCF adducts) vs. linear (AlCF adducts) M-N-N-LA motif (LA = Lewis acid), explained computationally as the result of steric repulsion. A striking difference arose when the formation of two-fold adducts was conducted. While in the case of BCF the 2 : 1 Lewis pairs could be observed in equilibrium with the 1 : 1 adduct and free borane but resisted isolation, AlCF forms robust 2 : 1 adducts trans-[ML2{(μ-η1:η1-N2)Al(C6F5)3}2] that isomerise into a more stable cis configuration. These compounds could be isolated and structurally characterized, and represent the first examples of trinuclear heterometallic complexes formed by Lewis acid-base interaction exhibiting p and d elements. Calculations also demonstrate that from the bare complex to the two-fold aluminium adduct, substantial decrease of the HOMO-LUMO gap is observed, and, unlike the trans adducts (1 : 1 and 1 : 2) for which the HOMO was computed to be a pure d orbital, the one of the cis-trinuclear compounds mixes a d orbital with a π* one of each N2 ligands. This may translate into a more favourable electrophilic attack on the N2 ligands instead of the metal centre, while a stabilized N2-centered LUMO should ease electron transfer, suggesting Lewis acids could be co-activators for electro-catalysed N2 reduction. Experimental UV-vis spectra for the tungsten family of compounds were compared with TD-DFT calculations (CAM-B3LYP/def2-TZVP), allowing to assign the low extinction bands found in the visible spectrum to unusual low-lying MLCT involving N2-centered orbitals. As significant red-shifts are observed upon LA coordination, this could have important implications for the development of visible light-driven nitrogen fixation.

Rotational Fingerprints of Vinylketene for Astronomical Observations

A high degree of isomerism in the realm of interstellar molecules stimulates systematic astronomical investigations of members of different families of isomers. Among them, vinyl-bearing compounds have kindled considerable interest due to recent detections of vinylamine, vinylacetylene, and vinylcyanoacetylene. Herein, we open the possibility to search for vinylketene in the interstellar space by means of its rotational transitions. The pure rotational spectrum of the title molecule was recorded in the frequency regions 195–218 and 293–324 GHz and an improved and extended set of spectroscopic parameters has been obtained for the most stable trans conformer. In addition, rotational signatures and molecular constants for the less stable cis form are reported for the first time. We provide a catalog of precise transition frequencies and intensities of vinylketene to the astronomical community and pave the way toward interstellar explorations of C4H4O isomer family.

Subtle hydrogen bond preference and dual Franck-Condon activity - the interesting pairing of 2-naphthol with anisole.

The hydrogen-bonded complexes between 2-naphthol (or β-naphthol) and anisole are explored by detecting their IR absorption in the OH stretching range as well as their UV absorption by means of laser-induced fluorescence and resonance-enhanced two-photon UV ionisation. For the more stable cis and the metastable trans conformations of the OH group in 2-naphthol, hydrogen bonding to the oxygen atom of anisole is consistently detected in different supersonic jet expansions. Alternative hydrogen bonding to the aromatic ring of anisole remains elusive, although the majority of state-of-the-art hybrid DFT functionals with London dispersion correction and - less surprisingly - MP2 wavefunction theory predict it to be slightly more stable at zero-point level, unless three-body dispersion correction is added to the B3LYP-D3(BJ) approach. This changes at the CCSD(T) level, which forecasts an energy advantage of 1-3 kJ mol-1 for the classical hydrogen bond arrangement even after including (DFT) zero-point energy contributions. The UV and IR spectra of the cis complex exhibit clear evidence for intensity redistribution of the primary OH stretch oscillator to combination states with the same low-frequency intermolecular bending mode by Franck-Condon-type vertical excitation mechanisms. This rare case of dual (vibronic and vibrational) Franck-Condon activity of a low-frequency mode invites future studies of homologues where aromatic ring docking of the OH group may be further stabilised, e.g. through anisole ring methylation.

Highly Conjugated Bis(benzo[b]phosphole)‐P‐oxides: Synthesis and Electrochemical, Optical, and Computational Studies

AbstractThe first examples of a π‐conjugated benzo[b]phosphole P‐oxide in which two phosphole P‐oxide units are connected by a carbon‐carbon double bond are described. The molecules are synthesized as E isomers with respect to the carbon‐carbon double bond and exist as stable cis and trans isomers (chiral and meso one respectively) relatively to the two stereogenic P atoms. The optical and electrochemical properties of both isomers have been investigated by experiment and computations.

Cis-trans isomerization of dimethyl 2,3-dibromofumarate.

The isomerization of dimethyl 2,3-dibromofumarate in chloroform solutions was investigated by the combination of nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations. The bromination of dimethyl acetylenedicarboxylate leading to dimethyl 2,3-dibromofumarate produces the trans isomer initially, which however converts into the more stable cis isomer. The conversion from trans to cis is spontaneous and greatly accelerated by light.

Selective Isomerization via Transient Thermodynamic Control: Dynamic Epimerization of trans to cis Diols.

Traditional approaches to stereoselective synthesis require high levels of enantio- and diastereocontrol in every step that forms a new stereocenter. Here, we report an alternative approach, in which the stereochemistry of organic substrates is selectively edited without further structural modification, a strategy with the potential to allow new classes of late-stage stereochemical manipulation and provide access to rare or valuable stereochemical configurations. In this work, we describe a selective epimerization of cyclic diols enabled by hydrogen atom transfer photocatalysis and boronic acid mediated transient thermodynamic control, selectively generating less stable cis products from the otherwise favored trans isomers. A range of substitution patterns and ring sizes are amenable to selective isomerization, including stereochemically complex polyols such as estriol, as well as syn to anti epimerization of acyclic vicinal diols. Moreover, this strategy has enabled the divergent epimerization of saccharide anomers, providing access to distinct sugar isomers from α- or β-configured glycosides.

Molecule alters circadian clock via light trigger

A light-activated molecule can reversibly shift the length of the circadian clock’s cycle in living cells and tissues ( Nat. Commun. 2021, DOI: 10.1038/s41467-021-23301-x ). The tool provides a targeted, noninvasive way to study how the clock affects cellular physiology, says Ben Feringa , a chemist at the University of Groningen who co-led the work. The clock, a signaling system that is found in nearly all organisms, keeps cells’ functions tied to a daily cycle. The team used an azobenzene moiety, which changes conformation from the stable trans isomer to the less stable cis isomer when exposed to light. The cis isomer gradually reverts to trans on its own, or it can be converted photochemically. The researchers added an azobenzene switch to a molecule called longdaysin. Longdaysin slows the clock by interfering with the action of a key regulator of the circadian clock. Violet light (400 nm) activates longdaysin in

Spectroscopy, Dynamics, and Hydration of S-Nitrosylated Myoglobin.

S-Nitrosylation, the covalent addition of NO to the thiol side chain of cysteine, is an important post-transitional modification that can alter the function of various proteins. The structural dynamics and vibrational spectroscopy of S-nitrosylation in the condensed phase are investigated for the methyl-capped cysteine model system and for myoglobin. Using conventional point charge and physically more realistic multipolar force fields for the -SNO group, it is found that the SN- and NO-stretch and the SNO-bend vibrations can be located and distinguished from the other protein modes for simulations of MbSNO at 50 K. The finding of stable cis- and trans-MbSNO agrees with experimental findings on other proteins as is the observation of buried -SNO. For MbSNO the observed relocation of the EF loop in the simulations by ∼3 Å is consistent with the available X-ray structure, and the conformations adopted by the -SNO label are in good overall agreement with the X-ray structure. Despite the larger size of the -SNO group compared with -SH, MbSNO recruits more water molecules in the first two hydration shells due to stronger electrostatic interactions. Similarly, when comparing the hydration between the A- and H-helices, they differ by up to 30% between WT and MbSNO. This suggests that local hydration can also be significantly modulated through nitrosylation.

Heteroleptic trivalent chromium in coordination chemistry: Novel building blocks for addressing old challenges in multimetallic luminescent complexes

Tailored heteroleptic trivalent chromium complexes combine kinetic inertness and structural control with tuneable photophysical properties, all aspects which are crucial for the design of a next gereneration of cheap (supra)molecular light-converting assemblies and devices. • Photoactive Cr(III) complexes as an alternative to precious Ru(II) complexes. • Lability-induced Cr(III) complexes as precursors for heteroleptic complexes. • Inert Cr(III)N 6 complexes might be exploited in metallo-supramolecular structures. • Cr(III)N 6 sensitizers can be programmed for providing long NIR excited state lifetimes. Although less famous than low-spin trivalent cobalt found in [Co III (NH 3 ) 6− x Cl x ]Cl 3− x ( x ≤ 3), which was exploited by Alfred Werner during the early part of the 20th century for establishing the basic rules of coordination chemistry, related trivalent chromium complexes exhibit comparable kinetic inertness, a rare property along the 3d-transition series. The associated slow isomerisation processes are compatible with the isolation of well-defined heteroleptic complexes. Some subtle energetic differences between Cr III -X (X = halide, pseudo-halide, cyanide, solvent) and Cr-N bonds can be exploited for preparing stable and inert cis / trans -[Cr(N ∩ N) 2 X 2 ] + and fac / mer -[Cr(N ∩ N ∩ N)X 3 ] primary heteroleptic complexes incorporating multidentate nitrogen-containing chelate ligands. The use of these building blocks within the frame of the ‘complex-as-ligand’ strategy, or via the labilization of the remaining Cr-X bonds pave the way for the design of discrete polymetallic assemblies in which the photophysically appealing [Cr III N 6 ] chromophores could find applications as functional light-converting devices.

Molecular dynamics investigation of the structural flexibility of H2O2 and H2S2 in response to medium polarity

Hydrogen peroxide (H2O2) and hydrogen persulfide (H2S2) are the simplest members of the peroxide and persulfide families, and both are signaling molecules that regulate several biological functions. Rotation about the O–O and S–S bonds impacts the strength of these molecules as H-bond donors or acceptors and tunes their polarity and stability by converting the polar equilibrium skewed structure (ϕHOOH ~ 112°, ϕHSSH ~ 91°) to the nonpolar less stable trans (ϕ = 180°) or the most polar and least stable cis (ϕ = 0°) conformers. The change in geometry in response to the structure and polarity of the microenvironment is an important feature that would influence how these molecules interact with or permeate through biological systems. Consistent with larger energy barriers for rotation about the S–S bond, quantum chemical calculations with MP2(full)/6–311++G(3df,3pd) reveal that when interacting with a single water, ethanol, or n-pentane molecule in the gas phase, the geometry of H2S2 is more rigid (ϕHSSH = 91 ± 3°) than that of H2O2 (ϕHOOH = 112 ± 8°). Molecular dynamics simulations of a single H2O2 or H2S2 in liquid water (ε = 80), ethanol (ε = 25), or n-pentane (ε = 2) reveal that, compared to the gaseous monomer, H2O2 maintains a more polar geometry in ethanol and water. Interestingly, the distribution of ϕHOOH significantly shifts towards the nonpolar conformation as solvent polarity decreases; the fraction of structures with ϕHOOH ≥ 160° is 0.10, 0.14, and 4.30% in water, ethanol, and n-pentane, respectively. The high-energy cis conformation of H2O2 was negligible in all solvents, especially in n-pentane. The equilibrium geometry of H2S2 is hardly influenced by solvent polarity and both cis and trans conformations are essentially absent in the three solvents. In contrast to rigid H2S2, H2O2 is thus a flexible molecule whose geometry depends on the environment polarity, a property that enables stabilizing H2O2 in different microenvironments and possibly plays a role in how biological systems discriminate between H2O2 and the rigid and polar close analog, H2O.

Additivity of retention of diastereoisomeric and enantiomeric arylphthalides, aryl(arylene)phthalides and aryldiphthalides of dyadic and triadic composition

For the first time, four series of new phthalide-containing heteroaromatic compounds were separated by reverse phase HPLC: OYO, OYS, SYS; OYOYO, OYOYS, SYOYS; SYSYS, SYSYO, OYSYO; OYYO, OYYS, SYYS, (where O – diphenyloxide, S – diphenylsulfide, Y – phthalide group). A fundamental difference was established in the chromatographic behavior of diaryl(arylene)diphthalides, built on the principle of “head-to-tail”, and diaryldiphthalides with a structure of “head-to-head”. The meso and chiral diastereoisomers of the former were eluted by one peak, while the latter existed in solution in the forms of stable cis (racemic form) and trans (meso form) rotamers with different retention times. It was shown that to calculate the retention times of related diarylphthalides, diaryl(arylene)phthalides, diastereoisomeric and enantiomeric diaryldiphthalides of an asymmetric structure, the half-sum rule can be applied according to which: tR(A-X-B)≈[(tR(A-X-A)+tR(B-X-B)]/2. For diaryl(arylene)diphthalides of a triadic structure, a modified additive scheme for calculating retention times is proposed, including multiplication and division operations: tR(A-A-A) = tR(A-A-B) × tR(A-B-B)/tR(B-B-B).

Visible Light Mediated Bidirectional Control over Carbonic Anhydrase Activity in Cells and in Vivo Using Azobenzenesulfonamides.

Two azobenzenesulfonamide molecules with thermally stable cis configurations resulting from fluorination of positions ortho to the azo group are reported that can differentially regulate the activity of carbonic anhydrase in the trans and cis configurations. These fluorinated probes each use two distinct visible wavelengths (520 and 410 or 460 nm) for isomerization with high photoconversion efficiency. Correspondingly, the cis isomer of these systems is highly stable and persistent (as evidenced by structural studies in solid and solution state), permitting regulation of metalloenzyme activity without continuous irradiation. Herein, we use these probes to demonstrate the visible light mediated bidirectional control over the activity of zinc-dependent carbonic anhydrase in solution as an isolated protein, in intact live cells and in vivo in zebrafish during embryo development.

Cis- and trans-Ligand Effects on the Inverse trans-Influence in [UVI(O)(L)Cl4]0/- (L = Unidentate Ligand) Complexes.

A comprehensive exploration of the inverse trans-influence (ITI) phenomenon in a series of cis-[UVI(O)(L)Cl4]0/- and trans-[UVI(O)(L)Cl4]0/- complexes involving a wide variety of neutral and anionic unidentate ligands L, using relativistic density functional theory, threw light on the still-intriguing physics of ITI, elucidated its origin, and deployed the ligands L in cis- and trans-ITI sequences (ladders). ITI is produced for the complete set of L in both series of [U(O)(L)Cl4]0/- complexes, but this is not reflected in the thermodynamic stability of the [U(O)(L)Cl4]0/- isomers. In effect the hard and strong σ-donor anionic ligands stabilize the trans isomers, but the opposite is true for the soft σ-donor/π-donor neutral and anionic ligands that stabilize the cis isomers. According to the ITI%(U-L) metrics the hard strong σ-donor anionic ligands exert stronger ITI than the soft σ-donor/π-donor neutral ones, while according to the ITI%(U-O) metrics ITI is produced only for the more stable trans-[U(O)(L)Cl4]0/- isomers involving the anionic ligands. In contrast the neutral ligands in the more stable cis-[U(O)(L)Cl4]0/- isomers produce the normal cis influence (CI). Furthermore, the more electronegative ligands produce stronger ITI. ITI%(U-O) cis- and trans-philicity ladders are also built for both series of complexes employing the isotropic σiso(SO) 17O NMR shielding constants as a sensitive metric of the ITI phenomenon. The NMR ITI%(U-O) metrics are consistent with the ITI%(U-O) ones illustrating that the isotropic 17O NMR shifts are sensitive metrics of the covalency of the multiple U-O bonding mode and, hence, of the ITI phenomenon. Interestingly the 2σ BD(U-O) natural bond orbitals play a key role in tuning the bond length and covalency of the U-O bond through the 2σ(U≡O) → 2σ*(U≡O) hyperconjugative interactions. The assessment of the magnitude of the ITI in the [UVI(O)(L)Cl4]0/- complexes and the recognition of the factors affecting ITI dispose a guide to experimentalists working in the area of uranium chemistry to develop strategies for stabilizing uranium-ligand linkages.

Clinically isolated syndrome, oligoclonal bands and multiple sclerosis

AbstractObjectiveClinically isolated syndrome (CIS) is a first demyelinating episode targeting the central nervous system. It can later fulfill the diagnostic criteria for multiple sclerosis (MS) or remain as a single event with no further clinical or paraclinical evidence of disease. Given the difficulty of predicting the long‐term course of the disease at the moment of the first episode, we intended to examine clinical and laboratory features associated with MS conversion, underlining the prognostic value of oligoclonal bands (OCBs) determination.MethodsWe analyzed patients with an episode compatible with CIS (not fulfilling the 2010 McDonald criteria) as the first manifestation of MS (according to the same criteria), observed in our MS clinic (n = 82).ResultsFrom our cohort, 76.8% of patients converted to MS. OCBs were present at baseline in 68.0% of MS patients, but also in 73.7% of stable CIS patients (P = .77). After stratification of the results by treatment, there was also no statistically significant association between the presence of OCBs and conversion to MS. Additionally, positive OCBs did not predict earlier conversion to MS.ConclusionsOur study outlines the high prevalence of positive OCBs in patients with CIS, even in those who, until now, do not fulfill the 2010 diagnostic criteria for MS. This raises questions about the early assumption of MS diagnosis based on OCB status. A very hasty diagnosis could result in chronic treatment initiation and a possibly lifelong stigma in patients who might never develop new lesions or have a second attack.

Kinetically unstable 2–isocyanophenol isolated in cryogenic matrices: Vibrational excitation, conformational changes and spontaneous tunneling

Monomers of 2-isocyanophenol were generated in low-temperature solid Ar and N2 matrices by UV-irradiation of benzoxazole and characterized by infrared (IR) spectroscopy. Near–IR narrowband excitation of the first OH-stretching overtone of 2–isocyanophenol isolated in an N2 matrix converted the most stable cis into the higher-energy trans conformer. Interconversions between these conformers also occurred when the sample was vibrationally excited by the full, or filtered, broadband light of the IR spectrometer source, notably, with different isomerization rate constants. A spontaneous trans → cis decay, via H–tunneling, was observed for N2 matrix kept in dark. In an Ar matrix, only the cis conformer was observed.

Synthesis of carbon nanohoops containing thermally stable cis azobenzene

Cycloparaphenylenes (CPPs) have been praised for their size-tunable HOMO/LUMO gap and associated electronic and optical properties, and have generated significant interest for small-molecule electronics. Another fascinating but less-explored prospect for CPPs involves exploiting their hollow geometry. With a rigid pore of tunable size and high electron density arising from the inward facing π-orbitals, CPPs are ideal for electron-poor guests. [10]CPP in particular has shown very high binding affinity for fullerene C60. The ability to reverse this encapsulation by external stimuli is an important next step. Herein we report the design and synthesis of two CPPs containing thermally stable cis azobenzene moieties in the conjugated framework, their behavior upon irradiation, and computational results evaluating their potential as photoswitchable fullerene hosts.