Formation and decay of pyrene radical cation and pyrene dimer radical cation in the absence and presence of cyclodextrins during resonant two-photon ionization of pyrene and sodium 1-pyrene sulfonate

摘要

Formation and decay of pyrene radical cation and pyrene dimer radical cation during resonant two-photon ionizations (T'PI) of pyrene (Py) and sodium 1-pyrene sulfomite (NaPySA) in the absence and presence of cyclodextrins were studied with visible and near IR transient absorption measurement using 355-nm laser flash photolysis technique.Ionization of Py and 1-pyrene sulfonate anion (PySA~-) occurred within the laser flash (5 ns) to give Py radical cation (Py~(centre not)) and PySA~- radical cation (Py~(centre not-)SA~-) having Py~(centre not-) chromophore.Dimerizations of Py':and Py and of Py~(centre not-)SA~- and PySA~- were observed to give the dimer radical cations (Py_2~(centre not) and Py_2~(centre not-) (SA~-)_2) based on time-resolved measurements of the charge resonance (CR) band.The TPI of PySA was also examined in the presence of beta- and gamma-cyclodextrins (betaCD and gammaCD,respectively).Py_2~(centre not-)(SA~-)_2 in the cavity of two gammaCDs having fully overlapped structure showed the CR band around 1700 nm,while Py_2~(centre not-)(SA~-)_2 in the cavity of two PCD having partially and fully overlapped structures indicated the CR bands around 1500 or 1700 nm.respectively.On the basis of formation and decay rates of Py_2~(centre not-)(SA~-)_2.bimolecular formation of Py_2~(centre not-)(SA~-)_2 and the neutralization are inhibited in the cavities of CDs.Selective formation of the fully overlapped structure of Py_2~(centre not-)(SA~-)_2 in the cavity of two yCDs within a laser flash is explained by direct TPI of two PySA s with the parallel structure of two Py chromophores in two PySA s in the cavity of two gammaCDs.