An Investigation of Triplet States, Radical Ions, and Triplet Excimers Produced by Laser Photoexcitation of Phenyldibenzophosphole in Fluid Solutions and Rigid Media

Abstract

Phenyldibenzophosphole (PDP), which is the phosphorus analogue of N-phenylcarbazole, yields excited singlet states, triplet states, radical cations, and anions, as well as excimeric species upon laser photoexcitation in fluid solutions or in rigid media such as polystyrene films. Delayed fluorescence occurs concurrently either by T-T annihilation or by the E-type process of thermally induced reverse intersystem crossing depending upon the solvent and the transient population of triplets. In solvents of high dielectric constant such as N,Ndimethylformamide (DMF) or ethanol/glycerol(30/70 V/V) (EtOH/glycerol), transient absorption signals due to triplet states and to radical cations and anions are observed. The purposeful introduction of electron donors or acceptors enhances the transient signals due to cations or anions, respectively, when D M F is the solvent. In EtOH/glycerol triplet excimers are produced by ion recombination, but in rigid media it appears that exciton migration and trapping a t excimer forming sites take place.

Some Photophysical Properties of Electronically Excited Phenyldibenzophosphole in Rigid Polymer Matrices

“…Both spectra contain the same features consisting of a shoulder at 370 nm, an emission maximum at 395 nm, a shoulder near 430 nm, a second peak at 470 nm, and an additional structure at 500 nm. Dilute solutions of PDP in frozen methyltetrahydrofuran (MTHF) glasses recorded in earlier work 15 produce a zero-zero phosphorescence band near 430 nm and a λ max at 470 nm. We conclude, therefore, that the extra bands at 370 and 395 nm are related to delayed fluorescence of PDP.…”

“…Removing residual ketonic impurities from polystyrene is known to be extremely difficult, and these residues luminesce at 15 K with origin near 390 nm and a peak near 420 nm. It must be pointed out that we erroneously characterized such a spectrum as being due to PDP in an earlier publication …”

“…It must be pointed out that we erroneously characterized such a spectrum as being due to PDP in an earlier publication. 15 Triplet states from these ketonic residues are produced in each excitation pulse, but when PDP is present in as little as 2% w/w, the ketonic triplets are completely quenched. The emission at 395 nm in Figures 1 and 2 was examined carefully because some of its features are similar to this impurity luminescence.…”

“…In earlier work on fluid solutions of PDP, 15 time resolution from a few hundred nanoseconds to several milliseconds was used, showing that the photophysics of PDP has the same dependence upon solvent dielectric constant as carbazolyl; that is, ionic processes predominate in high dielectric media and neutral excited states are the major species in low dielectrics. On the other hand, the lifetime of the PDP triplet, even in frozen matrices at 77 K was found to be on the order of 10 µs, but the apparatus used at that time was not suited for measuring longer time events.…”

Triplet Energy Migration in Poly(4-methacryloylbenzophenone-co-methyl methacrylate) Films: Temperature Dependence and Chromophore Concentration Dependence

“…Laser Photolysis. Transient absorption spectra and decays of BP X films were obtained by the laser photolysis system whose details have already been reported . Sample excitation was made by the 308-nm light (XeCl gas) pulse of a Questek Model 2110 excimer laser.…”