Diameter-Dependent Optical Absorption and Excitation Energy Transfer from Encapsulated Dye Molecules toward Single-Walled Carbon Nanotubes

Abstract

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.

Carbon Nanotubes for Photovoltaics: From Lab to Industry

“…In a related direction, endohedral filling of the SWCNTs with dye molecules may further extend the light harvesting capability of these solar cells, and photoinduced energy transfer from the organic dye to the s‐SWCNTs has already been observed with PL and photocurrent spectroscopy. [ 89 ] Molecules including quaterthiophene (4T), [ 90 ] squarylium dye (SQ), [ 89a,91 ] p,p′‐dimethylaminonitrostilbene (DANS), [ 92 ] and ferrocenylthiocarbonyl based dyes [ 93 ] have all been placed inside a SWCNT. However, these all require a minimum diameter of SWCNT (≈1.1 nm), [ 91,92 ] known as the sieving diameter, which places them outside the diameter range accessible to C 60 as an acceptor.…”

“…[ 89 ] Molecules including quaterthiophene (4T), [ 90 ] squarylium dye (SQ), [ 89a,91 ] p,p′‐dimethylaminonitrostilbene (DANS), [ 92 ] and ferrocenylthiocarbonyl based dyes [ 93 ] have all been placed inside a SWCNT. However, these all require a minimum diameter of SWCNT (≈1.1 nm), [ 91,92 ] known as the sieving diameter, which places them outside the diameter range accessible to C 60 as an acceptor. Furthermore, whilst dye filling will increase the visible/UV light absorption of the nanotube, it is important to remember that large diameter SWCNTs in combination with nonfullerene acceptors would already capture most of the incident light in the visible and IR regions.…”

Confinement of Dyes inside Boron Nitride Nanotubes: Photostable and Shifted Fluorescence down to the Near Infrared

“…Because of efficient energy transfer processes between dyes and SWCNT hosts ( E g < 1 eV), it became apparent that the dye fluorescence is readily quenched in most, if not all, of the nanohybrids with carbon nanotubes. [ 22,23 ] Hence, we turn our attention to the boron nitride nanotube (BNNT), which has a large bandgap ( E g ≈ 5.5 eV) [ 24,25 ] and hence high optical transparency over a wide range of wavelengths. In the context of life science, large diameter BNNTs ( d ≈ 50 nm) have been studied as cargo for drug delivery [ 26 ] and the toxicity in vivo and in vitro of different BNNTs is currently investigated in the field.…”

Structure of inorganic nanocrystals confined within carbon nanotubes

“…Their cylindrical shape and chemical structure (honeycomb carbon lattice) confer the material unique properties with potential applications in biomedicine [1,2], catalysis [3], nanocomposites [4] or electronics [5]. Their range of application can be further expanded by the formation of hybrid materials via endohedral filling [6][7][8][9] or external decoration [10,11]. The encapsulation at the nanoscale, which is the focus of the present review, allows tuning the properties of both the guest species that can undergo modifications of their space configuration, crystalline structure or the atomic ratio of their constituting elements [7] and the host, which electronic and optical properties can also be impacted due to the interaction between the new encapsulated material and the walls of the nanotubes [8,9].…”

“…Their range of application can be further expanded by the formation of hybrid materials via endohedral filling [6][7][8][9] or external decoration [10,11]. The encapsulation at the nanoscale, which is the focus of the present review, allows tuning the properties of both the guest species that can undergo modifications of their space configuration, crystalline structure or the atomic ratio of their constituting elements [7] and the host, which electronic and optical properties can also be impacted due to the interaction between the new encapsulated material and the walls of the nanotubes [8,9]. When discrete molecules of a material are confined inside the nanotubes their intermolecular interactions can be modified, compared to their bulk counterpart, leading to the formation of new nanostructures, resulting from rearrangements or chemical reactions between the confined species.…”