Emission from charge recombination during the pulse radiolysis of 9-cyano-10-phenylethynylanthracenes with donor and acceptor substituents

摘要

Emission from 9-cyano-10-phenylanthracene and 9-cyano-10-phenylethynylanthracenes having donor and acceptor substituents (RA = PA, PEA, OEA, NEA, and DEA) was studied with the time-resolved fluorescence measurement during the pulse radiolysis of RAs in benzene (Bz). PA and DEA showed only monomer emission, while other RAs (PEA, OEA, and NEA) showed both monomer and excimer emissions with much lower intensities. On the basis of the steady-state and transient absorption and emission measurements, the formation of RA in the singlet excited state ((1)RA*) can be attributed to the charge recombination between RA radical cation and anion (RA(center dot+) and RA(center dot-), respectively) which are initially generated from the radiolytic reaction in Bz. It is expected that for PA with a twisted geometry, the charge recombination between PA(center dot+) and PA(center dot-) occurs to give (1)PA* during the pulse radiolysis in Bz. For PEA and OEA, pi-stacking interaction is possible for the formation of an encounter complex during the charge recombination between RA(center dot+) and RA(center dot-). For NEA, it is expected that NEA(center dot+) and NEA(center dot-) collide neck-to-neck to generate the excimer due to the twisted geometry. For DEA, a considerably twisted structure is assumed to give (1)DEA* with strong ICT character but not (1)(DEA)(2)* because of the bulky donor substituent.