Effects of π-Conjugation Attenuation on the Photophysics and Exciton Dynamics of Poly(p-phenylenevinylene) Polymers Incorporating 2,2‘-Bipyridines

Abstract

The effect of π-conjugation attenuation on the photophysics and exciton dynamics of two conjugated polymers 1 and 2 are examined in solution. The structures of polymers 1 and 2 have 2,2′-bipyridyl-5-vinylene units that alternate with one and three 2,5-bis(n-decyloxy)-1,4-phenylenevinylene monomer units, respectively. The photophysics and exciton dynamics of polymers 1 and 2 were compared to those of the homopolymer, poly(2,5-bis(2′-ethylhexyloxy)-1,4-phenylenevinylene) (BEH-PPV). A series of changes in the photophysics of polymers 1 and 2 were found as a result of π-conjugation attenuation. These changes include blue shifts in absorption and emission spectra, spectral diffusion in stimulated emission, enhancement in photoluminescence quantum yields and lifetimes, and increases in photoinduced absorption intensities and lifetimes. These changes are systematically more pronounced in polymer 1 than in polymer 2 and are correlated with π-conjugation attenuation in the polymers due to twisting of the 2,2′-bipyridine groups about the 2,2′ single bond. An exciton dynamics model involving an ensemble of initial exciton states localized on oligomeric segments within the polymer with different conjugation lengths is proposed to describe the observed differences between polymers 1 and 2 and BEH-PPV. When the electronic coupling between these segments is strong, the polymer displays characteristics that are close to those of a one-dimensional semiconductor. However, when these couplings are weakened by groups, such as the 2,2′-bipyridine that attenuate π-conjugation, the polymer displays properties of an ensemble of oligomers.

Hierarchical assembly of light-emitting polymer nanofibers in helical morphologies

“…͑a͒ Fluorescence micrograph of a YEP helix loop: The highlighted fiber segments, labeled as "A," "B," and "C" are individually investigated. [28][29][30] The emission BS is indeed characteristic of molecular systems exhibiting less dense packing and reduced overlaps between different conjugated segments. Scale bar= 2 m. ͑b͒-͑d͒ PL ʈ ͑continuous lines͒ and PL Ќ ͑dotted lines͒ spectra by segment "A" ͑b͒, "B" ͑c͒, and "C" ͑d͒, respectively.…”

Macromolecules Containing Bipyridine and Terpyridine Metal Complexes: Towards Metallosupramolecular Polymers

“…Chen et al studied the effects of p conjugation on the photophysics and excitation dynamics of these polymers. [107] Relative to the homopolymers, they demonstrated blue shifts in their absorption and emission spectra, spectral diffusion in stimulated emission, and enhancement in their photoluminescence quantum yields and lifetimes. The ionochromic effects and structures of the metalated polymers were recently published.…”

A fluorescent chemosensor based on optically active 2,2′‐binaphtho‐20‐crown‐6 for metal ions

“…Conjugated polymers incorporating molecular recognition moieties can make use of the high sensitivity of these polymers to external structural perturbations and to electron density changes within the conjugated polymer backbone when they interact with metal ions to form complexes 13–16. The available sensitive detection methods employed for selective sensing of metal ions involve the design of ‘off–on’‐type fluorescent chemosensors based on the photo‐induced electron transfer and energy migration mechanism within the conjugated polymer main‐chain backbone 11, 12, 17–19…”