Electronic Energy Relaxation in a Photoexcited Fully Fused Edge-Sharing Carbon Nanobelt

Abstract

Carbon nanobelts are cylindrical molecules composed of fully fused edge-sharing arene rings. Because of their aesthetically appealing structures, they acquire unusual optoelectronic properties that are potentially suitable for a range of applications in nanoelectronics and photonics. Nevertheless, the very limited success of their synthesis has led to their photophysical properties remaining largely unknown. Compared to that of carbon nanorings (arenes linked by single bonds), the strong structural rigidity of nanobelts prevents significant deformations away from the original high-symmetry conformation and, therefore, impacts their photophysical properties. Herein, we study the photoinduced dynamics of a successfully synthesized belt segment of (6,6)CNT (carbon nanotube). Modeling this process with nonadiabatic excited state molecular dynamics simulations uncovers the critical role played by the changes in excited state wave function localization on the different types of carbon atoms. This allows a detailed description of the excited state dynamics and spatial exciton evolution throughout the nanobelt scaffold. Our results provide detailed information about the excited state electronic properties and internal conversion rates that is potentially useful for designing nanobelts for nanoelectronic and photonic applications.

Infinitene: Computational Insights from Nonadiabatic Excited State Dynamics

“…Adiabatic excited state energies, gradients, and NACR are calculated on-the-fly by means of the collective electronic oscillators (CEO) approach , at the configuration interaction single (CIS) level of theory using the semiempirical Hamiltonian Austin model 1 (AM1) . Previous studies have tested this approach for a number of similar carbon based molecules where we have found semiquantitative agreement with experimental data and a higher level of electronic structure methods. ,,,,− …”

“…Distinct absorption peaks in the UV region (250–400 nm) are attributed to contributions of multiple independent states that are joined in bands according to their proximity in energy owing to inhomogeneous density of excited states. The presence of energy gaps between these bands suggests long-lived states during the nonradiative relaxation from the high-energy photoexcitation. , …”

“…The presence of energy gaps between these bands suggests long-lived states during the nonradiative relaxation from the high-energy photoexcitation. 39,40 We start our NEXMD simulation after an initial photoexcitation at the maximum of the high-energy band (284 nm) by running 300 independent trajectories sampling rich conformational space of the molecule at ambient conditions (see Methods section). For this trajectory ensemble, the internal conversion process is monitored by the evolution of excited state populations grouped according to different sets of absorption bands and averaged across the entire ensemble as shown in Figure 1b.…”

“…A detailed description of the internal conversion process that takes place after photoexcitation of infinitene requires atomistic ab initio nonadiabatic excited state molecular dynamics simulations. − We make use of the NEXMD software package , that has been previously extensively used for the simulation of similar carbon nanohoops. − These simulations allow the analysis of relaxation pathways involved in the electronic and vibrational energy relaxation and redistribution that follow photoexcitation.…”

Exciton-vibrational dynamics induces efficient self-trapping in a substituted nanoring

“…[46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] These methods have been previously applied to simulate the photoinduced electronic energy relaxation and redistribution in CPPs and related nanohoops. 61,62 Particularly, the NEXMD (Nonadiabatic EXcited-state Molecular Dynamics) software package 44 has been extensively applied to a variety of CPPs, 5,8 and related nanohoops, 26,63 nanobelts 64 and nanocages. 65 These previous investigations have revealed that structural modifications introduced in CPPs by various substitutions and insertions induce changes in the relative efficiency of the internal conversion process involving dynamical changes of the structures such the local planarization of the chain and concomitant changes in the specific exciton spatial localization (self-trapping) 53 occurring during the excited-state dynamics.…”