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Ultrafast excited-state dynamics of nanoscale near-infrared emissive polymersomes.

ABSTRACT: Formed through cooperative self-assembly of amphiphilic diblock copolymers and electronically conjugated porphyrinic near-infrared (NIR) fluorophores (NIRFs), NIR-emissive polymersomes (50 nm to 50 microm diameter polymer vesicles) define a family of organic-based, soft-matter structures that are ideally suited for deep-tissue optical imaging and sensitive diagnostic applications. Here, we describe magic angle and polarized pump-probe spectroscopic experiments that: (i) probe polymersome structure and NIRF organization and (ii) connect emitter structural properties and NIRF loading with vesicle emissive output at the nanoscale. Within polymersome membrane environments, long polymer chains constrain ethyne-bridged oligo(porphinato)zinc(II) based supermolecular fluorophore (PZn n ) conformeric populations and disperse these PZn n species within the hydrophobic bilayer. Ultrafast excited-state transient absorption and anisotropy dynamical studies of NIR-emissive polymersomes, in which the PZn n fluorophore loading per nanoscale vesicle is varied between 0.1-10 mol %, enable the exploration of concentration-dependent mechanisms for nonradiative excited-state decay. These experiments correlate fluorophore structure with its gross spatial arrangement within specific nanodomains of these nanoparticles and reveal how compartmentalization of fluorophores within reduced effective dispersion volumes impacts bulk photophysical properties. As these factors play key roles in determining the energy transfer dynamics between dispersed fluorophores, this work underscores that strategies that modulate fluorophore and polymer structure to optimize dispersion volume in bilayered nanoscale vesicular environments will further enhance the emissive properties of these sensitive nanoscale probes.

SUBMITTER: Duncan TV

PROVIDER: S-EPMC2737527 | biostudies-other | 2008 Jul

REPOSITORIES: biostudies-other

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Ultrafast excited-state dynamics of nanoscale near-infrared emissive polymersomes.

Duncan Timothy V TV Ghoroghchian P Peter PP Rubtsov Igor V IV Hammer Daniel A DA Therien Michael J MJ

Journal of the American Chemical Society 20080709 30

Formed through cooperative self-assembly of amphiphilic diblock copolymers and electronically conjugated porphyrinic near-infrared (NIR) fluorophores (NIRFs), NIR-emissive polymersomes (50 nm to 50 microm diameter polymer vesicles) define a family of organic-based, soft-matter structures that are ideally suited for deep-tissue optical imaging and sensitive diagnostic applications. Here, we describe magic angle and polarized pump-probe spectroscopic experiments that: (i) probe polymersome structu ...[more]

PMID: 18611010

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Project description:While the influence of proquinoidal character upon the linear absorption spectrum of low optical bandgap ?-conjugated polymers and molecules is well understood, its impact upon excited-state relaxation pathways and dynamics remains obscure. We report the syntheses, electronic structural properties, and excited-state dynamics of a series of model highly conjugated near-infrared (NIR)-absorbing chromophores based on a (porphinato)metal(ii)-proquinoidal spacer-(porphinato)metal(ii) (PM-Sp-PM) structural motif. A combination of excited-state dynamical studies and time-dependent density functional theory calculations: (i) points to the cardinal role that excited-state configuration interaction (CI) plays in determining the magnitudes of S1 ? S0 radiative (kr), S1 ? T1 intersystem crossing (kISC), and S1 ? S0 internal conversion (kIC) rate constants in these PM-Sp-PM chromophores, and (ii) suggests that a primary determinant of CI magnitude derives from the energetic alignment of the PM and Sp fragment LUMOs (?EL). These insights not only enable steering of excited-state relaxation dynamics of high oscillator strength NIR absorbers to realize either substantial fluorescence or long-lived triplets (?T1 > ?s) generated at unit quantum yield (?ISC = 100%), but also crafting of those having counter-intuitive properties: for example, while (porphinato)platinum compounds are well known to generate non-emissive triplet states (?ISC = 100%) upon optical excitation at ambient temperature, diminishing the extent of excited-state CI in these systems realizes long-wavelength absorbing heavy-metal fluorophores. This work highlights approaches to: (i) modulate low-lying singlet excited-state lifetime over the picosecond-to-nanosecond time domain, (ii) achieve NIR fluorescence with quantum yields up to 25%, (iii) tune the magnitude of S1-T1 ISC rate constant from 109 to 1012 s-1 and (iv) realize T1-state lifetimes that range from ?0.1 to several ?s, for these model PM-Sp-PM chromophores, and renders new insights to evolve bespoke photophysical properties for low optical bandgap ?-conjugated polymers and molecules based on proquinoidal conjugation motifs.

Dataset Information

Ultrafast excited-state dynamics of nanoscale near-infrared emissive polymersomes.

Publications

Ultrafast excited-state dynamics of nanoscale near-infrared emissive polymersomes.

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