Strong π-π interaction of porphyrins on (6,5) carbon nanotubes with full surface coverage: Ab-initio calculations

Abstract

The stability, electronic, and optical properties of (6,5) single-walled carbon nanotubes (CNTs) functionalized with free-base tetraphenylporphyrin (TPP) molecules through π-stacking interactions are studied by ab-initio calculations. The stability and optical response of the CNT-TPP compounds for increasing CNT-surface coverage are investigated. Our results show that four TPP molecules forming a ring around the CNT is the most stable configuration, showing strong binding energies of about 2.5 eV/TPP. However, this binding energy can increase even more after additional molecules assemble side by side along the CNT, favoring the formation of a full single layer of TPP, as experimentally suggested. The strong π-π attractive forces induce molecular distortions that move the TPP higher-occupied molecular orbital levels inside the CNT bandgap, changing the optical response of the TPP molecules stacked on the CNT.

Single- and double-wall carbon nanotubes fully covered with tetraphenylporphyrins: Stability and optoelectronic properties from ab initio calculations

“…This CNT has a diameter of 7.7Å and can host up to four molecules around the perimeter, as previously established 22 . To describe the CNT periodicity along z, we use a supercell with a volume of (30 × 30 × a 0 )Å 3 , where a 0 is the CNT lattice constant, of 41.327Å.…”

“…3(a). This behavior can be explained for the position of the TPP HOMO levels which coincide with the CNT valence band maximum, inducing the rising of these levels inside the CNT band gap, as previously discussed for the (6,5)-4TPP compound 22 . Regarding the double-wall CNTs fully covered with TPP molecules, we observe essentially the same electronic properties than those of the single-wall CNT, unless a small shift to lower energies which is more pronounced for the semiconducting CNT species, as shown Figs.…”

“…For the metallic compounds (10,10)-5TPP and (10,10)@(5,5)-5TPP, we observe a similar behavior. Previously, we reported calculations for the TPP adsorption on the semiconducting (6,5) CNT, of 7.7Å in diameter, considering different concentrations of adsorbed molecules 22 . The most stable compound is found for a configuration of four TPPs covering the CNT perimeter, with a binding energy of 2.45 eV/TPP.…”

Ultrafast photochemistry of free-base porphyrin: a theoretical investigation of B → Q internal conversion mediated by dark states

“…[8][9][10][11][12][13] The electronic properties of these heterocyclic tetrapyrrolic pigments also play a key role in the formation of aggregates 14 and their functionalization in the context of lightharvesting, e.g. in solar cells, or as potential agents in photodynamic therapy 3,[15][16][17][18][19][20] . been investigated extensively, both experimentally and theoretically [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] .…”

Organic Molecular Tuning of Many-Body Interaction Energies in Air-Suspended Carbon Nanotubes

“…The interactions between the organic molecules and CNTs are considered to be less perturbative compared to covalent modification, and therefore the outstanding properties of CNTs can be preserved. Organic molecules such as porphyrin and phthalocyanine couple to nanotubes through π-π interactions to modify the charge density of CNTs, while the emission energy is reduced due to the molecular screening [10][11][12][13]. Furthermore, there are unique exciton dynamics at the organic molecule/CNT interface including energy and charge transfer [13][14][15][16][17].…”