Photochemical Behavior of Single-Walled Carbon Nanotubes in the Presence of Propylamine

Influence of local strain caused by cycloaddition on the band gap control of functionalized single-walled carbon nanotubes

Fine control of the band gap of single-walled carbon nanotubes (SWNTs) has been achieved by the functionalization with dibromoalkanes, namely, 1,3-dibromopropane (1a), 1,4-dibromobutane (1b), 1,5-dibromopentane (1c), and 1,8-bis(bromomethyl)naphthalene (1d). Red-shifted photoluminescence (PL) peaks observed at 1215–1242 nm were assigned to the local band gaps of the chemically functionalized SWNTs 2a, 2b, 2c, and 2d, respectively. Density functional theory (DFT) and time-dependent DFT calculations for 2a–2d suggest that “local strain” induced by cycloaddition plays an important role in tuning the local band gap energies of functionalized SWNTs.

The local strain at the addition is cited as another factor controlling the emission wavelength of functionalized SWNTs.

Control of near infrared photoluminescence properties of single-walled carbon nanotubes by functionalization with dendrons

Single-walled carbon nanotubes (SWNTs) were functionalized by reacting them with sodium naphthalenide and dendrons to control their photoemission in the near-IR region. The functionalized SWNTs were characterized by absorption, Raman, and photoluminescence (PL) spectroscopy. The degree of functionalization of the SWNTs decreased with the increasing bulkiness of the dendrons used. After functionalization, new red-shifted PL peaks could be observed at ∼1110 and ∼1210 nm where the intensities were drastically enhanced by the thermal treatment. The relative peak intensity of to that of increased with the increasing bulkiness of the dendrons. Density functional theory (DFT) calculations of the functionalized SWNTs with dendrons suggest that the adducts with less bulky hydroalkylated substitution are stable in Clar structures and the addition positions predominantly determine the PL peak positions.

Tuning of the photoluminescence and up-conversion photoluminescence properties of single-walled carbon nanotubes by chemical functionalization

Single-walled carbon nanotubes (SWNTs) were subjected to alkylation using alkyl bromide and alkyl dibromide, and the photoluminescence (PL) properties of the resulting alkylated SWNTs were characterized. Two new PL peaks were observed along with the intrinsic PL peak at 976 nm when alkyl bromide was used (SWNT-Bu: ∼1095 and 1230 nm, SWNT-Bn: 1104 and 1197 nm). In contrast, the use of α,α'-dibromo-o-xylene as an alkyl dibromide primarily resulted in only one new PL peak, which was observed at 1231 nm. The results revealed that the Stokes shift of the new peaks was strongly influenced by the addition patterns of the substituents. In addition, the time-resolved PL decay profiles of the alkylated SWNTs revealed that the PL peaks possessing a larger Stokes shift had longer exciton lifetimes. The up-conversion PL (UCPL) intensity of the alkylated SWNTs at excitation wavelengths of 1100 and 1250 nm was estimated to be ∼2.38 and ∼2.35 times higher than that of the as-dispersed SWNTs, respectively.

Control of the photoluminescence properties of single-walled carbon nanotubes by alkylation and subsequent thermal treatment

Alkylation and subsequent thermal treatment of SWNTs induces a new bright PL peak in the NIR region.