Photolysis of a Benzyne Precursor Studied by Time-Resolved FTIR Spectroscopy

The 266 nm laser flash photolysis of phtaloyl peroxide (<b>2</b>) in liquid acetonitrile solution at room temperature has been investigated. Upon 266 nm laser irradiation, <b>2</b> is effectively photodecarboxylated leading to the formation of <i>o</i>-benzyne (<b>1</b>) and two equivalents of CO₂, yet a small fraction of photolyzed <b>2</b> follows a different pathway leading to 6-oxocyclohexa-2,4-dienylideneketene (<b>3</b>) and one equivalent of CO₂. Compound <b>3</b> is kinetically reactive and reacts in the microsecond time scale following a first-order kinetic law. The presence of <b>1</b> in the photolysis experiment is confirmed by trapping experiments with methyl 1-methylpyrrole-2-carboxylate (<b>6</b>). The Diels–Alder reaction between <b>1</b> and <b>6</b> occurs under the selected experimental conditions on a time scale shorter than 100 ms

Femtosecond UV-pump mid-IR probe spectroscopy of the ultrafast photodissociation of azide radicals from an azidoiron(III) complex

The ultrafast photolysis of the cation complex [(cyclam-ac)FeN3]+ is studied by femtosecond spectroscopy with ultraviolet excitation and mid-infrared probing. Immediately after UV absorption, the excited complex undergoes internal conversion and azide dissociation within 2 ps. The subsequent vibrational relaxation in the electronic ground state and geminate recombination of the fragments take place on time scales of 13 and 20 ps, respectively

Femtosecond UV-pump mid-IR probe spectroscopy of the ultrafast photodissociation of azide radicals from an azidoiron(III) complex

The ultrafast photolysis of the cation complex [(cyclam-ac)FeN3]+ is studied by femtosecond spectroscopy with ultraviolet excitation and mid-infrared probing. Immediately after UV absorption, the excited complex undergoes internal conversion and azide dissociation within 2 ps. The subsequent vibrational relaxation in the electronic ground state and geminate recombination of the fragments take place on time scales of 13 and 20 ps, respectively

The Photochemical Route to Octahedral Iron(V). Primary Processes and Quantum Yields from Ultrafast Mid-Infrared Spectroscopy

Recently, the complex cation [(cyclam-ac)­Fe^III(N₃)]⁺ has been used in solid matrices under cryogenic conditions as a photochemical precursor for an octahedral iron nitride containing the metal at the remarkably high oxidation state +5. Here, we study the photochemical primary events of this complex cation in liquid solution at room temperature using femtosecond time-resolved mid-infrared (fs-MIR) spectroscopy as well as step-scan Fourier-transform infrared spectroscopy, both of which were carried out with variable-wavelength excitation. In stark contrast to the cryomatrix experiments, a photooxidized product cannot be detected in liquid solution when the complex is excited through its putative LMCT band in the visible region. Instead, only a redox-neutral dissociation of azide anions is seen under these conditions. However, clear evidence is found for the formation of the highly oxidized iron nitride product when the photolysis is carried out in liquid solution with UV light. Yet, the photooxidation must compete with photoreductive Fe–N bond cleavage leading to azide radicals and an iron­(II) complex. Both, redox-neutral and photoreductive Fe–N bond breakage as well as photooxidative N–N bond breakage occur on a time scale well below a few hundred femtoseconds. The majority of fragments suffer from geminate recombination back to the parent complex on a time scale of 10 ps. Upper limits of the primary quantum yield for photooxidation are derived from the fs-MIR data, which increase with increasing energy of the photolysis photon

Femtosecond two-photon ionization of fluid NH3 at 9.3 eV

Liquid and supercritical ammonia (NH3) is photo-ionized at an energy of 9.3 eV with 100-fs duration pulses at a wavelength of 266 nm. The ionization involves two photons and generates fully solvated electrons via the conduction band of the solvent within the time resolution of the experiment. The dynamics of their ensuing geminate recombination is followed in real time with femtosecond near-infrared (IR) probe pulses. The recombination mechanism can be understood as an ion-pair mediated reaction. The electron survival probability is found to be in quantitative agreement with the classical Onsager theory for the initial recombination of ions