The Effect of Protonation on the Optical Properties of Conjugated Fluorene–Pyridine Copolymers

Abstract

A series of conjugated alternating and statistical copolymers of fluorene and pyridine are synthesized and characterized. The compounds under investigation, namely poly[2,7-(9,9-dihexylfluorenyl)-alt-(2,6-pyridinyl)] and poly[2,7-(9,9-dihexylfluorenyl)-stat-(2,6-pyridinyl)], are prepared by a Suzuki-type cross-coupling reaction starting from commercially available materials utilizing the recently described catalyst trans-bis(dicyclohexylamine) palladiumdiacetate (''DAPCy''). The target compounds are investigated by nuclear magnetic resonance and infrared spectroscopy, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, thermal analysis, UV-Vis absorption spectroscopy, and luminescence measurements in solution and in the solid state. Special emphasis is placed on studying the consequences of protonation on the photophysical properties of the described materials. Achieving a concise microscopic understanding of the effects of protonation on the absorption and luminescence characteristics is crucial for potential applications in, e.g., optical sensors. To that aim, the results of the systematic studies of the photophysical properties are explained by quantum mechanical calculations.

Optical and electrochemical properties of polyfluorenes with pyridine–triphenylamine bipolar unit

“…In addition, the lowest energy absorption band is assigned to an ICT complex . The absorption maxima are comparable with those of PFs containing only 2,6‐pyridinyl, or TPA, , moieties in the main chain, but P1 and P2 exhibit a shoulder at 434 nm, in addition. The low intensities of these peaks indicate a weak oscillator strength of the ICT absorption bands and hence a small probability for the S o → 1 CT transition.…”

“…The redshift of the emission upon protonation has also been observed for other Py-containing polymers. 36,43 This emission may be attributed to the stabilization of the charge transfer state as the electronacceptor properties of Py are enhanced upon protonation. This is reasonable since only protonation of Py is expected.…”

Highly Efficient Color‐Stable Deep‐Blue Multilayer PLEDs: Preventing PEDOT:PSS‐Induced Interface Degradation

“…It is known from literature that polymers containing pyridine units,27 vinylene units28 or distinct end‐chain groups29 may be prone to degrade in an acidic environment. Therefore all copolymers have been tested for the possible influence of PEDOT:PSS to the emissive spectrum, and in particular that of the PSS‐rich phase at the interface.…”

pH‐responsive fluorescence chemical sensor constituted by conjugated polymers containing pyridine rings

“…In a previous study, Slugovc et al . reported that polyfluorene containing a pyridine ring showed pH‐dependent photoluminescence quenching and red‐shift of the emission peaks by charge transfer from fluorene units to pyridine units due to the protonation of the pyridine rings in solution . Thus, changes of fluorescence spectra suggested that the decrease of the fluorescence intensity could be attributed to the intra‐molecular charge transfer from the electron‐donor phenylene ethynylene units to the electron‐acceptor protonated pyridine units upon pH change.…”

“…These results indicated that the control of and changes of the spectroscopic properties of PPyPE could be achieved by protonation of pyridine units in the polymer (38,39). (40). Thus, changes of fluorescence spectra suggested that the decrease of the fluorescence intensity could be attributed to the intra-molecular charge transfer from the electron-donor phenylene ethynylene units to the electronacceptor protonated pyridine units upon pH change.…”