Triplet-triplet annihilation in a poly(fluorene)-derivative

Abstract

We report on measurements of phosphorescence (Ph) and delayed fluorescence (DF) in poly(2,7-(9,9-bis(2-ethylhexyl)fluorene)) (PF2/6) present as dilute solid solution, as well as in bulk films. From combined experimental investigations of the time and intensity dependence of DF and Ph, as well as the temperature dependence of DF, we are able to show that DF in PF2/6, both in solution and film, is dominated by triplet-triplet annihilation (TTA). As a consequence of the intrachain diffusion and, hence, relaxation of triplets, the kinetics of the bimolecular reaction show a turnover from dispersive to nondispersive regime as borne out by the DF decay. This is in accord with theoretical predictions of TTA in disordered solids. From the transition to equilibrium kinetics, we are able to estimate the width of the density of states of triplets to 40 meV in good agreement with the width of the inhomogeneous broadenend S0←T1 transition of PF2/6.

The contribution of triplet–triplet annihilation to the lifetime and efficiency of fluorescent polymer organic light emitting diodes

“…The consequence of such a high density of triplet excited states in conjugated polymers has been studied previously, where it was found that the triplet decay is dominated by their mutual 2011) bimolecular annihilation (TTA), 22,23 resulting in the production of emissive singlet excitons. Figure 3(a) shows the time resolved electroluminescence during the turn off of the prototypical device.…”

Singlet Generation from Triplet Excitons in Fluorescent Organic Light-Emitting Diodes

“…For the triplet signal, either triplet transient absorption [90,101] or phosphorescence [85] could be used. However, both require large excitation densities to yield appropriate signal-to-noise ratios, which also causes migration activated TTA a major quenching channel [102,103]. The situation becomes (relatively) worse at higher temperature, because triplet mobility increases-at room temperature triplet excitons decay essentially only by TTA, without any phosphorescence emission [49,104].…”

Temperature dependence of the exciton dynamics inDCM2:Alq3

“…(PBPMSi), σ = 94 meV [22]; and for poly(2,7-(9,9-bis(2-ethylhexyl)fluorene)) (PF2/6), σ = 40meV [12]. In contrast, DCM2:Alq 3 films possess considerably less disorder as reflected in their narrow DOS.…”

“…Previous work has reported on the temperature dependence of triplet exciton transport in benzophenone glass [11], intrachain triplet diffusion and TTA in both solution and bulk films of a poly(fluorene) derivative [12], and triplet energy transfer in conjugated polymers [13][14][15]. While the dynamics of singlet excitons vs. temperature were explored in neat Alq 3 [16], to our knowledge the temperature dependence of emissive singlet and non-emissive triplet states has yet to be systematically studied in an efficient small molecule fluorescent guest-host system.…”