Strong main-chain length-dependence for the β-phase formation of oligofluorenes

Abstract

Poly-/oligofluorenes are promising luminescent materials applicable in organic light emitting diodes, lasers, etc. In particular, the β-phase structure, in which the fluorene main chain adopts a planar conformation with extended conjugation, shows characteristic optical properties. In this study, we have synthesized oligo(9,9'-dioctylfluorenes) whose chain lengths (n) are n = 9, 12, 15, 18, 21, 24 and 27 mers.Interestingly, the β-phase formation of the oligofluorenes is observed remarkably for oligofluorenes with n > 15, which is confirmed by the UV/vis and fluorescence spectroscopy. This study elucidates the structure-property relationship required to design high performance fluorene-based materials. Such a chainlength-dependent optical property provides useful information for utilizing the materials in many applications.

Questions of Mirror Symmetry at the Photoexcited and Ground States of Non-Rigid Luminophores Raised by Circularly Polarized Luminescence and Circular Dichroism Spectroscopy: Part 1. Oligofluorenes, Oligophenylenes, Binaphthyls and Fused Aromatics

“…Oligo- and polyfluorenes bearing alkyl chains in the 9,9-positions of the fluorene ring are known to be excellent emitters with a high PLQY of greater than 0.9 at ambient temperature, even in solution [ 81 , 82 , 83 ]. The C 2v -symmetrical fluorene ring has V-shaped topology in a planar geometry and can be regarded as a twistable biphenyl derivative (Ph2).…”

Origin of the Anisotropy and Structure of Ellipsoidal Poly(fluorene) Nanoparticles

“…Additionally, the extended conjugation length of β-phase regions causes a red-shift of the absorption wavelength as opposed to the amorphous phase, revealed by a sharp absorption peak at around 440 nm (Figure 1.4a). 10,45 These optical properties are also visible in the fluorescence emission.…”

“…Investigations on the optical properties of poly(fluorene) materials, for example by fluorescence measurements, gave insights on length and conformation of the conjugated backbone. 9,10 As a detailed understanding of the processes involved in polymer chain arrangement enables an improved control over particle morphologies and optoelectrical material properties, the investigation of nanoscale materials based on poly(fluorene) is of high interest.…”

Poly(9‐undecyl‐9‐methyl‐fluorene) and poly(9‐pentadecyl‐9‐methyl‐fluorene): Synthesis, solution structure, and effect of side chain asymmetry on aggregation behavior

“…Considering specifically PF8, its phase behavior can be controlled by a variety of parameters including: solvent quality as illustrated by Kitts and Vanden Bout, mixing a poor with a good solvent as shown by Lu and coworkers, and the polymer molecular weight as indicated by Vanden Bout and coworkers and by detailed studies of oligofluorenes by Fytas, Nakashima, and coworkers . Poorer solvents and higher molecular weight polymers promote the β phase and aggregation.…”

“…13,14 Considering specifically PF8, its phase behavior can be controlled by a variety of parameters including: solvent quality as illustrated by Kitts and Vanden Bout, 15 mixing a poor with a good solvent as shown by Lu and coworkers, 16,17 and the polymer molecular weight as indicated by Vanden Bout and coworkers 18 and by detailed studies of oligofluorenes by Fytas, Nakashima, and coworkers. 19,20 Poorer solvents and higher molecular weight polymers promote the β phase and aggregation. More generally, for linear side chain PFs, the same behavior can be controlled by the side chain length 21,22 and by the polymer concentration, [23][24][25] with smaller side chain length and higher polymer concentrations promoting the tendency to aggregate, even in the good solvent toluene.…”