Triplet states in derivatives of polyfluorene and polyspirobifluorene

Abstract

Studies of the triplet excitons in polyspirobifluorene have been carried out principally the techniques of photo induced absorption and gated emission. Specifically the nature of the origin of the delayed emission has been investigated. In dilute solutions delayed fluorescence is attributed to intrachain triplet-triplet annihilation, whereas in thin films the delayed fluorescence is shown to originate from both inter and intra chain annihilation processes. In dilute solutions the use of time resolved photo induced absorption has proven the production of triplets via intersystem crossing. In addition in dilute solutions the observation of triplet-triplet annihilation in the absence of singlet-singlet annihilation has shown that the singlet excitons are relatively immobile along the chains compared with the triplet excitons. In addition to the triplet studies of PSBF, investigations were made into oligomers of the polyfluorene derivative Pf 2/6. Absorption and photo induced absorption studies have shown that the triplet exciton is intrinsically confined to approximately 5 repeat units of the polymer, whereas the singlet occupies a considerably larger conjugation length of approximately 25 units. In another derivative, PFO the effect of the presence of the P-phase on the photo induced absorption spectra has been investigated for both poor solvents and in films. Principally a shifted photoinduced absorption spectrum is observed along with the features for the amorphous polymer, in addition the low luminescence of the P-phase allows a higher transition of the triplet to be observed. Finally we have shown that it is possible to manipulate the rate of guest host triplet back transfer between the phosphor and the polymer host in an organic phosphor doped polymer system by exploiting the short range nature of Dexter energy transfer. Derivatives of Ir(PPY)3 with bulky side groups were shown to have a reduced rate of back transfer in comparison to the unsubstituted Ir(PPY)3 complex.