Photolysis Of Azide Research Articles

Optimization of fluorinated phenyl azides as universal photocrosslinkers for semiconducting polymers

Fluorinated phenyl azides (FPA) enable photo-structuring of π-conjugated polymer films for electronic device applications. Despite their potential, FPAs have faced limitations regarding their crosslinking efficiency, and more importantly, their impact on critical semiconductor properties, such as charge-carrier mobility. Here, we report that azide photolysis and photocrosslinking can achieve unity quantum efficiencies for specific FPAs. This suggests preferential nitrene insertion into unactivated C‒H bonds over benzazirine and ketenimine reactions, which we attribute to rapid interconversion between the initially formed hot states. Furthermore, we establish a structure‒activity relationship for carrier mobility quenching. The binding affinity of FPA crosslinker to polymer π-stacks governs its propensity for mobility quenching in both PM6 and PBDB-T used as model conjugated polymers. This binding affinity can be suppressed by FPA ring substitution, but varies in a non-trivial way with π-stack order. Utilizing the optimal FPA, photocrosslinking enables the fabrication of morphology-stabilized, acceptor-infiltrated donor polymer networks (that is, PBDB-T: ITIC and PM6: Y6) for solar cells. Our findings demonstrate the exceptional potential of the FPA photochemistry and offer a promising approach to address the challenges of modelling realistic molecular interactions in complex polymer morphologies, moving beyond the limitations of Flory‒Huggins mean field theory.

Investigating the formation of metal nitride complexes employing a tetradentate bis-carbene bis-phenolate ligand

The synthesis of MnV and CrV nitride complexes of a pro-radical tetradentate bis-phenol bis-N-heterocyclic carbene ligand H2LC2O2 were investigated. Employing either azide photolysis of the MnIII precursor complex MnLC2O2(N3) or...

Metal-Organic Framework Thin Films as Ideal Matrices for Azide Photolysis in Vacuum.

Studies on reactions in solutions are often hampered by solvent effects. In addition, detailed investigation on kinetics is limited to the small temperature regime where the solvent is liquid. Here, we report the in situ spectroscopic observation of UV-induced photochemical reactions of aryl azides within a crystalline matrix in vacuum. The matrices are formed by attaching the reactive moieties to ditopic linkers, which are then assembled to yield metal-organic frameworks (MOFs) and surface-mounted MOFs (SURMOFs). These porous, crystalline frameworks are then used as model systems to study azide-related chemical processes under ultrahigh vacuum (UHV) conditions, where solvent effects can be safely excluded and in a large temperature regime. Infrared reflection absorption spectroscopy (IRRAS) allowed us to monitor the photoreaction of azide in SURMOFs precisely. The in situ IRRAS data, in conjunction with XRD, MS, and XPS, reveal that illumination with UV light first leads to forming a nitrene intermediate. In the second step, an intramolecular rearrangement occurs, yielding an indoloindole derivative. These findings unveil a novel pathway for precisely studying azide-related chemical transformations. Reference experiments carried out for solvent-loaded SURMOFs reveal a huge diversity of other reaction schemes, thus highlighting the need for model systems studied under UHV conditions.

Photochemical Synthesis of a Stable Terminal Uranium(VI) Nitride.

Terminal uranium nitrides have so far proven impossible to isolate by photolysis of azides. Here we report the second ever example of an isolated terminal uranium(VI) nitride. We show that the terminal nitride [NBu4][U(OSi(OtBu)3)4(N)], 3, can be prepared upon photolysis with UV light of the U(IV) azide analogue. This is achieved by careful tailoring of the azide precursor and of the reaction conditions. Complex 3 is stable under ambient conditions but reacts readily with electrophiles (H+ and CO).

Imidoylnitrenes R'C(═NR)-N, Nitrile Imines, 1H-Diazirines, and Carbodiimides: Interconversions and Rearrangements, Structures, and Energies at DFT and CASPT2 Levels of Theory.

The structures, energies, and rearrangements of imidoylnitrenes H-C(═NH)-N, H2N-C(═NH)-N, Ph-C(═NH)-N, H-C(═NPh)-N, and MeO-C(═NCN)-N (10a-e) are investigated at DFT and CASPT2 levels of theory. Imidoylnitrenes are potentially formed by pyrolysis or photolysis of azides, tetrazoles (6, 6'), or sydnones. Unlike most acylnitrenes, the imidoylnitrenes 10 have triplet ground states. The first excited states are the open-shell singlets (OSSs), lying between ca. 4 and 20 kcal mol-1 above the triplets at the CASPT2 level. The second excited states are the closed-shell singlets (CSSs), lying >50 kcal mol-1 higher in energy. The OSS imidoylnitrenes can ring-close to 1H-diazirines 9 with very low activation energies (2-12 kcal mol-1), and the 1H-diazirines can then rearrange to nitrile imines 8 with activation energies of 37-48 kcal mol-1. Conversely, nitrile imines generated directly by pyrolysis or photolysis of 2,5-substituted tetrazoles 6 can rearrange to 1H-diazirines 9 and imidoylnitrenes 10 with activation energies of 37-60 kcal mol-1. Finally, the imidoylnitrenes 10 can rearrange to carbodiimides 11 with modest activation barriers of 12-20 kcal mol-1. Calculated vibrational data, UV-vis spectra, and spin densities in the triplet states are also reported, and zero-field splitting parameters |D/hc| in the range 0.9-1 cm-1 and nonzero |E/hc| values are predicted.

Capturing Conformation‐Dependent Photoreactivity of Crystalline 3‐Azido‐1,3‐diphenylisobutyrophenone

AbstractSolid‐state photolysis of 3‐azido‐1,3‐diphenyl‐isobutyrophenone 1 results in selective formation of isobutyrophenone 2 and benzonitrile 3. X‐ray structure analysis of azide 1 demonstrates that the conformer (1Cr) adopted for packing in the crystal lattice has the carbonyl moiety perpendicular to the α‐phenyl group (Ph‐C=O torsional angle of 85°). Laser flash photolysis of azide 1 nanocrystals allows direct detection of the lowest excited triplet ketone (TK) of 1Cr (λmax≈475 nm). Thus, in crystals, 1 is proposed to react via the TK state to cleave the Cβ−Cγ bond. Time‐dependent density functional theory (TD‐DFT) calculations verify that the energy of the TK of 1Cr is 79 kcal mol−1 above the ground state (S0), and thus TK has sufficient energy for cleavage of the Cβ−Cγ bond to form products 2 and 3, further supporting this solid‐state reaction mechanism.

Direct Observation of 4-Phenoxyphenylnitrenium Ion: A Transient Absorption and Transient Resonance Raman Study

Femtosecond (fs) and nanosecond (ns) transient absorption (TA) and single pulse transient resonance Raman spectroscopic investigation of the intermediates after laser photolysis of 4-phenoxyphenyl azide in acetonitrile and mixed aqueous solution is reported. fs-TA results show that the singlet 4-phenoxyphenylnitrene was produced immediately after photolysis of the azide. Then, the singlet nitrene underwent intersystem crossing (ISC) and ring expansion to generate triplet nitrene and ketenimine in acetonitrile with t = 346 ps or protonation in mixed aqueous solution with t = 37 ps, respectively, a little slower than the counterparts of the methoxy one (108 and 5.4 ps for ISC and protonation processes, respectively). The transient Raman spectrum combined density functional theory (DFT) calculation predicting the structure and vibrational frequencies suggested that phenoxyphenylnitrenium ion has a comparable quinoidal character to that of methoxy- and ethoxy-phenylnitrenium ions. All of these results indicated that the phenoxy substitution has some impact on the reactivity of phenylnitrene but a slight influence on the structure of phenylnitrenium ion.

Modulating Solubility and Enhancing Reactivity of Photo-Cross-Linkable Poly(styrene sulfonyl azide-alt-maleic anhydride) Thin Films

To formalize our understanding of indiscriminate grafting chemistries as they pertain to cross-linkable polymers and emerging patterning technologies, we designed a new polymer, poly(styrene sulfonyl azide-alt-maleic anhydride) (PSSMA). By modulating its solubility, it can be deposited into smooth, ultrathin films atop polar and nonpolar polymers. Upon heating above 120 °C or exposure to UV light, highly reactive nitrene intermediates are generated from the azide groups which form covalent adducts and cross-link the PSSMA. Azide photolysis and polymer gelation were studied in the context of a statistical model to gain insight into the network outcomes of nitrenes in a polymer film. For every azide group converted to a nitrene in ambient atmosphere, it has an 11% likelihood of grafting to another chain and a 5% chance of causing a scission. These values can be increased over 3-fold by reducing the O2 content by 85%. Alternatively, the effects of quenching by ground-state O2 can be mitigated by adding Michler’s ketone (MK) to the film. PSSMA/MK blend films possess a 39% (±13) likelihood for grafting and 29% (±10) for scission. The higher ratio of scission to grafting is a consequence of the sensitized azides producing triplet-state nitrenes, which favor hydrogen abstraction. These broadly generalizable considerations will be useful to others who wish to maximize light sensitivity in related polymer systems.

Triplet sensitized photolysis of a vinyl azide: direct detection of a triplet vinyl azide and nitrene.

Photolysis of vinylazide 1, which has a built-in acetophenone triplet sensitizer, in argon-saturated toluene results in azirine 2, whereas irradiation in oxygen-saturated toluene yields cyanide derivatives 3 and 4. Laser flash photolysis of azide 1 in argon-saturated acetonitrile shows formation of vinylnitrene 1c, which has a λmax at ∼300 nm and a lifetime of ∼1 ms. Vinylnitrene 1c is formed with a rate constant of 4.25 × 10(5) s(-1) from triplet 1,2-biradical 1b. Laser flash photolysis of 1 in oxygen-saturated acetonitrile results in 1c-O (λmax = 430 nm, τ ≈ 420 μs acetonitrile). Density functional theory (DFT) calculations were used to aid in the characterization of the intermediates formed upon irradiation of azide 1 and to validate the proposed mechanism for its photoreactivity.

Thermolysis of 3-Azido-N-Phenylthieno-[2,3-b]pyridine-2-Carboxamides

Annelated 1,4-diazepines are of interest as they are often compounds possessing different forms of biological and pharmacological activity [1]. Many methods for the synthesis of diazepines have been reported up until now, but the search for novel methods still of interest for scientific community. One of the known methods for closing a diazepine ring is the intramolecular transformation of aromatic azides. The formation of the diazepine ring occurs via photolysis of azides [2] or by an intramolecular cycloaddition of the azide group at a carbon–carbon multiple bond [3-6]. Continuing our study on the synthesis of 1,4-diazepines condensed with a thienopyridine fragment [7] we have developed a method for the preparation of polycyclic 1,4-diazepine derivatives based on the thermal decomposition of thieno[2,3-b]pyridine azides 2a-c. We have selected the N-phenyl-substituted tertiary 3-aminothieno[2,3-b]pyridine-2-carboxamides 1a-c as starting materials and carried out successive diazotization and azide formation reactions to give the corresponding azides 2a-c.

Sensitized photolysis of stearic acid azide

In an IR-spectroscopic study of the sensitized photolysis of stearic acid azide in a solution of benzene, it was found that the introduction of Michler’s ketone into the system decreased the efficiency of isocyanate formation by a factor of about 10. It was hypothesized that the azide photolysis in the presence of Michler’s ketone can be explained by the formation of a complex of the acyl azide with the ketone in a triplet excited state, a displacement of electron density from the acyl azide group, and its degradation with the formation of a triplet acylnitrene, which is incapable of rearranging into isocyanate.

Aromatic polyethers with 2,6-bis(4-azidotetrafluorobenzylidene)cyclohexanone side fragments and styryl groups in the backbone

140 Aromatic polyethers (APEs) with perfluorophe nylene fragments in the backbone have a number of valuable properties such as high thermal and chemical stabilities, good mechanical and insulating properties, and low water absorption. Therefore, these polymers are promising for aerospace industry and microelec tronics [1–3]. We suggested that APEs of this type containing additionally 2,6 bis(4 azidotetrafluorobenzylide ne)cyclohexanone fragments and styryl groups in the backbones of the macromolecules may present practi cal interest as binders of thermally stable negative pho toresists. Note that new styryl containing bisphenols that have been recently synthesized [4] are suitable as building blocks in the design and synthesis of APE, which are promising, in our opinion, for the produc tion of such photoresists. However, such APEs have not yet been reported. In this work, we propose for the first time a strategy for the synthesis of azide containing APEs with styryl groups in the macromolecule backbones. We per formed a facile and convenient synthesis of such unsaturated polymers by exhaustive esterification of APEs containing carboxyl side groups by 2,6 bis(4 azidotetrafluorobenzylidene) 4 (2 hydroxyethyl)cyc lohexanone (bisazide OH). In addition, thermal transformations of the synthesized polymers and their photochemical curing induced by the products of photolysis of azide containing fragments were stud ied, and the systems were evaluated as negative photo resists.

Functionalization of carbon nanotubes and other nanocarbons by azide chemistry

Abstract Following the conventional carbon allotropes of diamond and graphite, fullerene, carbon nanotubes (CNTs) and graphene as 0D, 1D and 2D graphitic macromolecules have been discovered recently in succession, declaring the unlimited potential of carbon-based nanomaterials and nanotechnology. Although CNTs exhibit significant potential applications in advanced materials and other fields due to their extraordinary mechanical strength and electrical/thermal conductivity properties, their low solubility, poor wettability and bad dispersibility in common solvents and solid matrices have limited their processing and applications. Thus, the attempt to achieve wettable/processable CNTs by functionalization has attracted increasing attention in both scientific and industrial communities. In recent years, azide chemistry has been demonstrated as a powerful means to covalently modify CNTs. It consists of two major approaches: click chemistry and nitrene chemistry, which both involve the usage of various azide compounds. The former one is based on highly reactive and stereospecifical Cu(I) catalyzed azide-alkyne cycloaddition reaction; the latter one is based on the electrophilic attack to unsaturated bonds of CNTs with nitrenes as reactive intermediates formed from thermolysis or photolysis of azides. In this mini-review paper, the azide chemistry to functionalize CNTs is highlighted and the corresponding functionalization routes to build CNT-based complex structures are also discussed. Besides, covalent functionalizations of other graphitic nanomaterials such as fullerence and graphene, via azide chemistry, are commented briefly.

Uranium azide photolysis results in C–H bond activation and provides evidence for a terminal uranium nitride

Uranium nitride [U[triple bond]N](x) is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U[triple bond]N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U-N=N=N) precursor. The transient U[triple bond]N fragment is reactive and undergoes insertion into a ligand C-H bond to generate new N-H and N-C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C(6)F(5))(3). These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C-H bonds.

Triplet-sensitized photolysis of alkoxycarbonyl azides in solution and matrices

Photolysis of azides 1– 4 in methanol, which have a built-in intramolecular triplet sensitizer, yields mainly carbamates 5– 8. Laser flash photolysis of 1– 4 shows formation of their triplet-excited ketone, which decays by intramolecular energy transfer to form triplet nitrenes 1n– 4n. Irradiating 1– 3 in matrices yields isocyanic acid, whereas photolysis of 4 forms isocyanate 4i. The depletion rate of the azide bands between 2100 and 2200 cm −1 is different than the rate of formation for the isocyanic acid bands at ∼2265 cm −1; thus, the formation of isocyanic acid is a stepwise process. Irradiating 1 in matrices produces an absorption band due to nitrene 1n ( λ max ∼ 343 nm), which is depleted upon further irradiation, whereas the absorption due to 4-acetyl benzaldehyde ( λ max ∼ 280 nm) increases with prolonged irradiation. We propose that formation of isocyanic acid in matrices must come from secondary photolysis of nitrenes 1n– 3n. This mechanism is further supported by calculation, which show that the estimated transition state for 1n– 4n to fall apart to yield alkoxy and cyanato radicals is only ∼34 kcal/mol above the ground state of the triplet nitrenes and thus the cleavage can take place photochemically. Thus, nitrenes 1n– 4n can be formed selectively, but these intermediates are highly photosensitive and undergo secondary photolysis in matrices.

The Rules Governing the Formation of Silver Azide Photolysis Products

Irradiation of silver azide at λ = 365 nm (I > 1 × 1015 quantum cm−2 s−1) in a vacuum (1 × 10−5 Pa) leads to an increase in the rate of photolysis and photoinduced current and the appearance of a new long-wave region of spectral sensitivity. The photolysis products, silver metal and gaseous nitrogen, are formed in a stoichiometric ratio on the surface of silver azide. The rate constants for silver azide photolysis were determined. Measurements of contact potential difference, current—voltage characteristics, photoelectromotive force, and photocurrent showed that AgN3(A1)—Ag (photolysis product) microheterogeneous systems were formed in silver azide photolysis. The limiting stage of silver azide photolysis is the diffusion of interstitial silver cations to the (TnAgm)0 neutral center.

Ultrafast Spectroscopic and Matrix Isolation Studies of p-Biphenylyl, o-Biphenylyl, and 1-Naphthylnitrenium Cations

p-biphenylyl, o-biphenylyl, and 1-naphthyl azides were deposited in argon at low temperature in the presence and absence of HCl. In the absence of HCl, the known electronic and vibrational spectra of the corresponding triplet nitrenes, azirines, and didehydroazepines were observed, whereas in the presence of HCl, photolysis of these azides produces new electronic spectra assigned to the corresponding nitrenium cations. For p-biphenylyl azide the resulting spectrum of the nitrenium ion is very similar to the previously observed solution-phase spectrum of this species. The vibrational spectrum of this cation was recorded for the first time. Spectroscopic evidence for the previously unknown o-biphenylylnitrenium cation and 1-naphthylnitrenium cation are provided. The spectra of p- and o-biphenylylnitrenium cations and 1-naphthylnitrenium cation are well reproduced by CASSCF and CASPT2 calculations. The same nitrenium cations were detected in solution by femtosecond time-resolved laser flash photolysis of the appropriate azides in 88% formic acid. The transient spectra of the nitrenium cations recorded in solution are in good agreement with the spectra obtained in HCl matrices. The rates of formation of these cations equal the rates of decay of the singlet nitrenes in 88% formic acid and are as follows: p-biphenylyl (taugrowth = 11.5 ps), o-biphenylyl (taugrowth = 7.7 ps), and 1-naphthylnitrenium cations (taugrowth = 8.4 ps). The decay lifetimes of p- and o-biphenylylnitrenium cations are 50 and 27 ns, respectively. The decay lifetimes of 1-naphthylnitrenium cation is 860 ps in 88% formic acid.

The Cl to NCl branching ratio in 248-nm photolysis of chlorine azide

The primary reaction products from 248-nm chlorine azide photolysis are identified in a collision-free experiment. In contrast to all previous reports, the radical channel producing Cl + N 3 (95 ± 3%) is seen to dominate the photochemistry. The molecular channel producing NCl + N 2 (5 ± 3%) was also observed.

Photolysis of Compressed Sodium Azide (NaN3) as a Synthetic Pathway to Nitrogen Materials

The potential syntheses of pure nitrogen materials may involve photolysis of azide compounds. In this work, compressed solid samples of NaN3 were photolyzed in gem anvil cells at pressures up to 5.0 GPa. Reaction rates and mechanisms for the photolytic processes were studied using single-shot time-resolved (microsecond scale) absorption spectroscopy. Two broad absorption bands due to reaction intermediates were observed at 300 and 700 nm. Tentative assignments of the reaction intermediates and their reaction rates were used to help elucidate the potential for high-pressure syntheses of novel nitrogen structures. Finally, recovered products were analyzed with infrared and Raman vibrational spectroscopy.

Photocrosslinking reaction of vinyl‐functional polyphenylsilsesquioxane sensitized with aromatic bisazide compounds

AbstractPhotochemical reactions of aromatic azide groups were applied for a novel photosensitive silicone ladder polymer, that is, partially vinyl‐substituted polyphenylsilsesquioxane sensitized with aromatic bisazide compounds as a photocrosslinker. The photocrosslinking reaction in this system was investigated from the viewpoint of the efficiency of the photocrosslinker, that is, the ratio of the photocrosslinker consumed for crosslinking. The numbers of photodecomposed azide groups and crosslinks in the polymer were determined by Fourier transform infrared measurements. At a higher bisazide concentration, the predominant reaction of nitrenes formed as the intermediary radical by the photolysis of azide was a coupling reaction that could not contribute to the gelation of the polymer. The ratio of the bisazide compound consumed for crosslinking showed the highest value at its concentration of 3 wt % and decreased with the addition of a larger amount. The semiempirical molecular orbital calculations were applied to the theoretical analysis of the photoreaction of nitrenes using phenylnitrene as a model structure. The calculation results indicated that the coupling reaction of nitrenes should proceed more easily than the photocrosslinking reaction in N2 atmosphere, and the fact that the oxidation of nitrenes should proceed exclusively in the atmosphere including O2 agreed with the experimental results. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4196–4205, 2001