Star‐like polyfluorenes based on 2,4,6,8, 10,12‐hexabenzyl‐2,4,6,8,10,12‐hexaazaisowurtzitane caged‐core: toward non‐aggregating, blue‐light‐emitting polymers

Zhao, Qian-jin; Wu, Wenhui

doi:10.1002/pat.1548

Cited by 3 publications

(1 citation statement)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The photophysical and electronic properties of various p-conjugated oligomers and polymers sensitively depend on their conformations and packing structures in condensed phases (solutions, films, and amorphous solids). For example, it has been demonstrated that oligothiophene ( n T, n = 6) aggregates exhibited a blue-shift in absorption spectra relative to the isolated molecule, probably due to the increase in the twisted structures and the decrease in the effective conjugation length (ECL). − On the contrary, most polyfluorenes (PFs), which are famous for their strong luminescence and facile color-tuning via structural modifications, were observed to undergo a small red-shift about 1–18 nm in absorption spectra of films relative to those of solutions. − How do you explain the different trends in spectra shifts upon aggregation for n Ts and PFs? This work aims to present a general picture for understanding the (red or blue) shift in adsorption spectra from the (increasing or reducing) contents of planar-conjugated conformations through a systematic study on the absorption spectra of PFs.…”

Section: Introductionmentioning

confidence: 99%

Role of Planar Conformations in Aggregation Induced Spectral Shifts of Supermolecular Oligofluorenols in Solutions and Films: A Combined Experimental and MD/TD-DFT Study

et al. 2015

View full text Add to dashboard Cite

The supramolecular approach of fluorenol polymers brings about excellent self-assembly behavior to fabricate organogels and superstructured thin films through highly directional noncovalent interactions. To understand the aggregation effects on electronic structures, the packing structures and the UV/vis absorption spectra of oligofluorenols (PFOHn, n = 1/3-8), with and without OC8H17 side chains, were studied experimentally and theoretically in crystal, amorphous solids, and solutions, respectively. For the ground state in vacuum the steric repulsion between two adjacent fluorenol units renders the PFOH oligomers twisted in a helix conformation, while the molecular aggregation favors the appearance of planar π-conjugated structures. In comparison with the crystal packing, the content of planar conformation (with the torsion angle less than 20°) is increased in amorphous solids. The hydroxyl groups in oligofluorenols facilitate the formation of hydrogen bonding networks. The red shift in absorption spectra was observed in a systematic experimental study of unsubstituted and substituted oligofluorenols with the increasing concentration both in toluene and chloroform solutions. The subsitituted oligofluorenol R-PFOH1 with only one OC8H17 side chain exhibited a shoulder peak at 430-440 nm, which is different from PFOH1 without side chain and 3R-PFO1 with three OC8H17 side chain. Time-dependent density functional theory (TDDFT) calculations, which were carried out on conformation ensembles taken from a series of molecular dynamics (MD) simulations, revealed that the increase in the content of planar π-conjugated conformations is correlated to the red shift in the absorption spectra upon increasing the solution concentrations. The aggregation-induced red-shift in absorption spectra of oligofluorenols, as well as the blue-shift for oligothiophenes, was rationalized in a unified way from the increased (and reduced) content of planar conformations in molecular aggregates.

show abstract