1,4-Diiodobenzene is a biochemical reagent that can be used as a biological material or organic compound for life science related research.1,4-Diiodobenzene was used in total synthesis of martinellic acid, a naturally occurring bradykinin receptor antagonist. It is used as a precursor in the preparation of martinellic acid and 1,4-bis(p-R-phenylethynyl)benzenes.

Ultrafast photodissociation dynamics of 1,4-diiodobenzene

The photodissociation dynamics of 1,4-diiodobenzene is investigated using ultrafast time-resolved photoelectron spectroscopy. Following excitation by laser pulses at 271 nm, the excited-state dynamics is probed by resonance-enhanced multiphoton ionization with 405 nm probe pulses. A progression of Rydberg states, which come into resonance sequentially, provide a fingerprint of the dissociation dynamics of the molecule. The output beam is split, with 90% seeding an optical parametric amplifier (OPA) (Coherent, OPerA Solo) that generates the pump pulse (4.58 eV, 0.05 eV FWHM, 2.4 μJ pulse energy) and 10% upconverted to the second harmonic using a β-barium borate (BBO) crystal as the probe pulse (3.06 eV, 0.04 eV FWHM, 8.0 μJ pulse energy). Both beams are focused perpendicularly onto a molecular beam created by heating solid 1,4-diiodobenzene to 140 °C to generate ～14 Torr of vapor which is seeded in 1.1 bars of He gas. The present investigation probes the photodissociation dynamics of 1,4-Diiodobenzene using time-resolved pump-probe photoelectron spectroscopy. Following excitation at 271 nm, the dynamics of it is probed by multiphoton ionization via molecular Rydberg states using 405 nm photons. [1]

A Shimadzu UV-1700 double-beam scanning spectrometer (20 W, halogen lamp) was used to obtain the UV-visible absorption spectrum of 1,4-diiodobenzene from 190 nm to 400 nm. A small amount of a solid sample was placed in the bottom of a sealed quartz cuvette with a path length of 1 cm, and the pressure was allowed to equilibrate before measurement of the vapor. Upon excitation with a 4.58 eV laser pulse, 1,4-diiodobenzene is found to dissociate via an ultrafast indirect dissociation pathway. The initially excited 5B1 and 6B1 bound states decay into the repulsive 3B1 and 2B1 states with a 33 ± 4 fs time constant. As the molecule travels down the repulsive surfaces, the probe laser pulse comes into resonance with molecular Rydberg states in a sequential fashion.

Sterically crowded 1,4-diiodobenzene as a precursor

A bulky 1,4-Diiodobenzene having four adjacent para-tBu-C6H4 group (Ar') substituents (1) was used to prepare the di-hypervalent iodine compound 1,4-[I(OAc)2]2-2,3,5,6-Ar'4-C6 (2). Despite the steric encumbrance of the iodine center by the flanking aryl substituents, compound 2 undergoes ready cyclization under mild conditions (excess CF3COOH at 55 °C, 30 min) to afford a dicyclic di-iodonium di-triflate salt. The single crystal structures of compounds 2 was examined and compared to the formerly characterized precursor 1. The para-tert-butyl groups on these compounds also render the compounds more soluble than multifunctional hypervalent iodine (HVI) compounds. HVI compounds having multiple iodine(III) centers are increasingly of interest for applications as recyclable reagents, materials precursors, and as Lewis acids.[2]

Femtosecond photodissociation dynamics of 1,4-diiodobenzene

Scientists present a multifaceted investigation into the initial photodissociation dynamics of 1,4-diiodobenzene (DIB) following absorption of 267 nm radiation. We combine ultrafast time-resolved photoelectron spectroscopy and X-ray scattering experiments performed at the Linac Coherent Light Source (LCLS) to study the initial electronic excitation and subsequent rotational alignment, and interpret the experiments in light of Complete Active Space Self-Consistent Field (CASSCF) calculations of the excited electronic landscape. The initially excited state is found to be a bound 1B1 surface, which undergoes ultrafast population transfer to a nearby state in 35 ± 10 fs. The internal conversion most likely leads to one or more singlet repulsive surfaces that initiate the dissociation. This initial study is an essential and prerequisite component of a comprehensive study of the complete photodissociation pathway(s) of 1,4-Diiodobenzene at 267 nm. Assignment of the initially excited electronic state as a bound state identifies the mechanism as predissociative, and measurement of its lifetime establishes the time between excitation and initiation of dissociation, which is crucial for direct comparison of photoelectron and scattering experiments.[3]

References

[1]Stankus B, Zotev N, Rogers DM, Gao Y, Odate A, Kirrander A, Weber PM. Ultrafast photodissociation dynamics of 1,4-diiodobenzene. J Chem Phys. 2018 May 21;148(19):194306. doi: 10.1063/1.5031787. PMID: 30307219.

[2]Li G, Smith R, Gembicky M, Rheingold AL, Protasiewicz JD. Sterically crowded 1,4-diiodobenzene as a precursor to difunctional hypervalent iodine compounds. Chem Commun (Camb). 2022 Jan 25;58(8):1159-1162. doi: 10.1039/d1cc06486j. PMID: 34981095.

[3]Stankus B, Budarz JM, Kirrander A, Rogers D, Robinson J, Lane TJ, Ratner D, Hastings J, Minitti MP, Weber PM. Femtosecond photodissociation dynamics of 1,4-diiodobenzene by gas-phase X-ray scattering and photoelectron spectroscopy. Faraday Discuss. 2016 Dec 16;194:525-536. doi: 10.1039/c6fd00135a. PMID: 27711844.