Photoinduced Nonadiabatic\nDynamics of a Single-Walled\nCarbon Nanotube-Porphyrin Complex

Single-walled carbon nanotubes (SWCNTs) have gained a\nlot of attention\nin the past few decades due to their promising optoelectronic properties.\nIn addition, SWCNTs can form complexes that have good chemical stability\nand transport properties with other optical functional materials through\nnoncovalent interactions. Elucidating the detailed mechanism of these\ncomplexes is of great significance for improving their optoelectronic\nproperties. Nevertheless, simulating the photoinduced dynamics of\nthese complexes accurately is rather challenging since they usually\ncontain hundreds of atoms. To save computational efforts, most of\nthe previous works have ignored the excitonic effects by employing\nnonadiabatic carrier (electron and hole) dynamics simulations. To\nproperly consider the influence of excitonic effects on the photoinduced\nultrafast processes of the SWCNT-tetraphenyl porphyrin (H2TPP) complex\nand to further improve the computational efficiency, we developed\nthe nonadiabatic molecular dynamics (NAMD) method based on the extended\ntight binding-based simplified Tamm–Dancoff approximation (sTDA-xTB),\nwhich is applied to study the ultrafast photoinduced dynamics of the\nnoncovalent SWCNT-porphyrin complex. In combination with statically\nelectronic structure calculations, the present work successfully reveals\nthe detailed microscopic mechanism of the ultrafast excitation energy\ntransfer process of the complex. Upon local excitation on the H2TPP\nmolecule, an ultrafast energy transfer process occurs from H2TPP (SWCNT-H2TPP*)\nto SWCNT (SWCNT*-H2TPP) within 10 fs. Then, two slower processes corresponding\nto the energy transfer from H2TPP to SWCNT and hole transfer from\nH2TPP to SWCNT take place in the 1 ps time scale. The sTDA-xTB-based\nelectronic structure calculation and NAMD simulation results not only\nmatch the previous experimental observations from static and transient\nspectra but also provide more insights into the detailed information\non the complex’s photoinduced dynamics. Therefore, the sTDA-xTB-based\nNAMD method is a powerful theoretical tool for studying the ultrafast\nphotoinduced dynamics in large extended systems with a large number\nof electronically excited states, which could be helpful for the subsequent\ndesign of SWCNT-based functional materials.