Spiroconjugation-Enhanced Intramolecular Charge-Transfer State Formation in a Polyspirobifluorene Homopolymer

Abstract

In this work we demonstrate the complex excited-state behavior of polyspirobifluorene in the solid state, which, due to the interaction of the spiroconjugated side group, readily forms a charge-transfer (CT) excited state of lower energy than the singlet exciton. The polymer is compared to standard polyfluorene materials using pump-probe and field-assisted pump-probe spectroscopy. It has been found that the small energy barrier between the singlet exciton and the CT state allows for population of the emissive singlet state at room temperature giving rise to a long tail in the singlet lifetime compared to an apparent single-exponential lifetime at low temperature. It is proposed that in devices the CT state is populated on charge recombination before the singlet states are excited by electron transfer from the CT state.

(2,1‐a)‐Indenofluorene Derivatives: Syntheses, X‐ray Structures, Optical and Electrochemical Properties

“…[27] Other similar red shift between spiro and nonspiro derivatives have been also reported in the literature and notably assigned to spiroconjugation. [49,65,66] Consequently, the larger red shift observed in the absorption spectra between (2,1-a)-IF and (2,1-a)-DSF-IF (16-17 nm), similar to that observed by Ohe and co-workers (19 nm), may be assigned to the specific face-to-face arrangement of the two spirofluorene units. Indeed, the electronic influence on the indenofluorene core of a cofacial fluorene p-dimer as found in (2,1-a)-DSF-IF, should be different than that of two non-directly interacting fluorene units as found in (1,2-…”

Structure–property relationship of 4-substituted-spirobifluorenes as hosts for phosphorescent organic light emitting diodes: an overview

“…First, the E T of SBF has been reported at 2.87 eV being slightly lower than that of its building block fluorene (E T =2.92 eV). 81 The slight conjugation between the two fluorene units in SBF (called spiroconjugation) 91,[98][99][100][101][102] decreases the E T of SBF by ca 0.05 eV compare to fluorene. 81,91 All the PHC derivatives exclusively built on ortho linkages possess a similar E T , measured at 2.77 eV for 4-Ph-SBF and close to 2.80 eV for the oligo-SBFs, 4,4'-(SBF) 2 , 4,4'-(SBF) 3 , 4,4'-(SBF) 4 or 4,4'-(SBF) 5 .…”

The Use of Substituted Iridium Complexes in Doped Polymer Electrophosphorescent Devices: The Influence of Triplet Transfer and Other Factors on Enhancing Device Performance

“…Finally, T h is the population of triplets on the host; it is assumed that in the time regime of the build-up of the polymer triplets, there is no decay of the polymer triplets. [22] 2. Results and Discussion…”