Implications of relaxation dynamics of collapsed conjugated polymeric nanoparticles for light-harvesting applications

Abstract

The conjugated polymer-based nanostructures have been explored extensively from energy harvesting to healthcare applications due to their unique photophysical properties. This perspective includes the mechanism of the formation of polymer...

Ultrafast Relaxation Dynamics of Conjugated Polymer Nanoparticles by Tuning Their Interchain Interactions

“…The interchain interactions between individual chromophoric subunits dominate the intrachain interactions after the formation of PNPs from the pristine polymer. 9,57 The effective conjugation length is governed by these interactions. The difference in the absorption spectra indicates the difference in packing, coiling, and conformational orientation of the polymer chains in P 1 , P 2 , and P 3 , which was evident from the MD simulation results.…”

“…7,8,15,19−24 The polymeric chains stay far apart in suitable solvents, which is their extended form, and polymer chains can coil together, forming a collapsed state in polar solvents. 2,9,25 The photophysical properties significantly differ due to interchain interactions, which eventually control the excitedstate decay kinetics. 9,20,25,26 The electronic excitation in the collapsed state is not confined to a single chromophoric subunit and is coherently delocalized over many chromophoric units.…”

“…Semiconducting conjugated polymers are attractive for efficient designing of organic photovoltaics because of their multi-chromophoric nature, large absorption cross-section, and good photo-stability. − The understanding of the complex excited-state relaxation dynamics of conjugated polymers is important for designing an efficient solar energy harvester. − They contain multiple quasi-localized chromophores (chromophoric sub-units) with a different degree of delocalized π-electrons. − After absorbing photons, the transition of a delocalized electron occurs from the ground to the excited state. ,,− The excited-state properties of these systems largely depend on the spatial orientation of these chromophoric sub-units and the conformational dynamics of polymer chains, which control their intra- and inter-chain interactions. ,,,− The polymeric chains stay far apart in suitable solvents, which is their extended form, and polymer chains can coil together, forming a collapsed state in polar solvents. ,, The photophysical properties significantly differ due to interchain interactions, which eventually control the excited-state decay kinetics. ,,, The electronic excitation in the collapsed state is not confined to a single chromophoric sub-unit and is coherently delocalized over many chromophoric units. , It is known as the incoherent hopping process instead of coherent exciton motion. − The competition between intrachain exciton motion and interchain hopping is nicely depicted in conjugated polymer films in J-aggregates . Hu et al have reported remarkable changes in the photophysical properties in the collapsed state of the poly­[2-methoxy-5-(2-ethylhexyloxy)-1,4 phenylenevinylene] (MEH-PPV) polymer due to interchain interaction .…”

“…The collapsed state of a conjugated polymer can be crystalline or amorphous, or a mixture of both the domains can co-exist. In an aqueous medium, most of the hydrophobic polymer chains coil together and form polymer nanoparticles (PNPs), which is a manifestation of the amorphous collapsed state. , The PNPs have a broad range of applications encompassing photovoltaics, organic light-emitting diodes, white light generation, singlet oxygen generation, bio-imaging, and photo-catalysis because of their low toxicity, bio-compatibility, and photo-stability along with superior optical and electronic properties. ,,− …”

Deciphering the Relaxation Mechanism of Red-Emitting Carbon Dots Using Ultrafast Spectroscopy and Global Target Analysis

“…Reisner and co-workers have realized as many as 398 μmol of photocatalytic H 2 production per gram of C-dots per hour in the presence of a nickel co-catalyst . Significant efforts have been devoted to the synthesis and applications of C-dots; however, the study of the excited-state relaxation of C-dots using ultrafast spectroscopy and global and target analysis is less explored, which is essential for the development of efficient light-harvesting systems. − Wang et al have proposed an intrinsic dark state and a surface-related emissive state, which relaxes independently in the case of a carbon nanodot . On the contrary, previous works report the excitation transfer from the core to surface with various time scales ranging from 400 fs to 10 ps. , Yang and co-workers have demonstrated a detailed interplay between the core and surface in the excited state. , Wen et al have identified the time scale for various processes for the excited state of C-dots such as surface trapping (400 fs), optical phonon scattering (<5 ps), acoustic phonon scattering (50 ps), and excitonic recombination (1.5 ns) .…”