The
hollow cores and well-defined diameters of single-walled carbon
nanotubes (SWCNTs) allow for creation of one-dimensional hybrid structures
by encapsulation of various molecules. Absorption and near-infrared
photoluminescence-excitation (PLE) spectroscopy reveal that the absorption
spectrum of encapsulated 1,3-bis[4-(dimethylamino)phenyl]-squaraine
dye molecules inside SWCNTs is modulated by the SWCNT diameter, as
observed through excitation energy transfer (EET) from the encapsulated
molecules to the SWCNTs, implying a strongly diameter-dependent stacking
of the molecules inside the SWCNTs. Transient absorption spectroscopy,
simultaneously probing the encapsulated dyes and the host SWCNTs,
demonstrates this EET, which can be used as a route to diameter-dependent
photosensitization, to be fast (sub-picosecond). A wide series of
SWCNT samples is systematically characterized by absorption, PLE,
and resonant Raman scattering (RRS), also identifying the critical
diameter for squaraine filling. In addition, we find that SWCNT filling
does not limit the selectivity of subsequent separation protocols
(including polyfluorene polymers for isolating only semiconducting
SWCNTs and aqueous two-phase separation for enrichment of specific
SWCNT chiralities). The design of these functional hybrid systems,
with tunable dye absorption, fast and efficient EET, and the ability
to remove all metallic SWCNTs by subsequent separation, demonstrates
potential for implementation in photoconversion devices.
Single-wall carbon nanotubes (SWCNTs) possess unique electronic and optical properties that depend strongly on their exact chiral structure. Recent progress in the structure sorting of specific SWCNT chiralities, with increasing chiral purity[1], demands an effective characterization methodology to be developed to accurately determine the chiral composition of any SWCNT chirality. Very often, optical spectroscopy is used to assess the chiral composition of a sample, but absorption cross-sections, PL quantum efficiencies and Raman cross-sections are all depending on the exact chiral structure,[2] and can be strongly influenced by other factors such as the specific internal and external environment of the SWCNTs.[3] In this work, we systematically compare the chirality distribution obtained from 3 different optical spectroscopic techniques, i.e. absorption, wavelength-dependent Raman and fluorescence-excitation spectroscopy with the chirality distribution obtained from high-resolution transmission electron microscopy for both chirality-sorted and unsorted SWCNT samples. This combined approach demonstrates the importance of using a multi-technique characterization strategy for a reliable determination of SWCNT chirality distribution.[4]
[1] J.A. Fagan, Nanoscale Adv. 1, 3307 (2019) and references therein
[2] V.N. Popov, Nano Lett. 4, 1795 (2004)
[3] S. Cambré et al, Angew. Chem. – Int Ed. 50, 2764 (2011); ACS nano 6, 2649 (2012)
[4] A. Castan et al, Carbon 171, 968 (2021)
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