Laser flash photolysis studies and magnetic field effect on a new heteroexcimer between N-ethylcarbazole and 1,4-dicyanobenzene in homogeneous and heterogeneous media

Abstract

The electron transfer (ET) process between a fluorophore (N-ethylcarbazole) and a quencher (1,6dicyanobenzene) has been studied by absorption, steady-state and time-resolved fluorescence and laser flash photolysis techniques in homogeneous and micellar media. The effect of a magnetic field on the ET process of this system has also been carried out by flash photolysis. The results reflect the following unique features of this system. The reduction potentials of the acceptor and the donor are such that the exciplex formation is possible by ET, moreover, as the charge separation is small a weak exciplex is formed even in a highly polar solvent, e g . acetonitrile (MeCN). Thus, the exciplex formation and solvent-separated ion pair (SSIP) formation in MeCN take place simultaneously. The experimentally obtained bimolecular quenching constant, k, , from the Stern-Volmer plot, agrees satisfactorily with theoretically calculated k, for an ET reaction applying Marcus theory. The exciplex formation inside the micellar medium enables us to study the magnetic field effect (MFE) on this exciplex system. The simultaneous occurrence of the exciplex and radical ion pair in MeCN as well as the formation of the exciplex within the micellar environment, most probably for the first time, ensure a special characteristic of this exciplex system. Another novel feature is the abnormal behaviour of this system in benzene, which has also been discussed here.

Lifetime Quenching of the Fluorophore: A Signature of Magnetic Field Maximization

“…The fluorescence lifetimes of ECZ in BZ, EA, THF and ACN are very close to each other, e.g. 7.5, 7.2, 7.3 and 7.2 ns, respectively, as reported earlier (25,26); however, it increases by about 1 ns in DMF. Because a smaller amount of DMF is added to a larger volume of THF to maintain the desired polarity range that is quite low here, the lifetime of ECZ remains almost the same in the mixed solvents of THFDMF.…”

“…The extent of dielectric enrichment depends on the Z, the index of preferential solvation by where p is the solute molecules dipole moments, M and 6 are the solvent mean molecular weights and densities, respectively, Af(D),,* = f(D1) -f(D2) where DI and D2 are the dielectric constants of the solvent where D1 < D2 and r is the distance from the solute dipole center. Thus, where p is greater then Z will be more, and dielectric enrichment should be profound for Py-DMA, as the dipole moment of the exciplex is greater compared to ECZ-DCB (25).…”

Magnetic Field Effect: A Tool for Identification of Spin State in a Photoinduced Electron-Transfer Reaction

“…Therefore, if an equilibrium exists between singlet and triplet RIPs, formation of different types of products are possible. During last two decades it has been observed that the application of a low magnetic field (MF) on this ET process − has remarkable potential in identification of original spin states of the RIPs as well as in controlling the production of cage/escape products by modulating the spin states, i.e., by disturbing the existing equilibrium between the singlet and triplet states. If it is assumed that RIPs are formed initially in the singlet state, equilibrium will exist between a singlet and three degenerate triplet states.…”

Simultaneous Occurrence of Energy Transfer and Photoinduced Electron Transfer in Interactions of Hen Egg White Lysozyme with 4‐Nitroquinoline‐1‐Oxide

“…Laser flash photolysis study. The transient absorption spectra of lysozyme–4NQO system was measured by nanosecond laser flash photolysis (Applied Photophysics) using a Nd:YAG laser (Lab series, Model Lab 150, Spectraphysics) that was described earlier (22). The sample was excited with a 266 nm laser pulse with FWHM = 8 ns.…”