Nonradiative Excited‐State Decay via Conical Intersection in Graphene Nanostructures

Abstract

Chemical groups are known to tune the luminescent efficiencies of graphene-related nanomaterials, but some species, including the epoxide group (À COCÀ ), are suspected to act as emissionquenching sites. Herein, by performing nonadiabatic excitedstate dynamics simulations, we reveal a fast (within 300 fs) nonradiative excited-state decay of a graphene epoxide nanostructure from the lowest excited singlet (S 1 ) state to the ground (S 0 ) state via a conical intersection (CI), at which the energy difference between the S 1 and S 0 states is approximately zero. This CI is induced after breaking one CÀ O bond at the À COCÀ moiety during excited-state structural relaxation. This study ascertains the role of epoxide groups in inducing the nonradiative recombination of the excited electron-hole, providing important insights into the CI-promoted nonradiative deexcitations and the luminescence tuning of relevant materials. In addition, it shows the feasibility of utilizing nonadiabatic excited-state dynamics simulations to investigate the photophysical processes of the excited states of graphene nanomaterials. Computational DetailsThe ground-and excited-state properties were studied by density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively, as implemented by the Gaussian 09[a] S.

Interplay of molecular dynamics and radiative decay of a TADF emitter in a glass-forming liquid

“…17 We note that the change in thermal energy is modest over this range because the temperature decreased by only 33% relative to its initial value at 300 K. If the rate of non-radiative decay k NR changed significantly with temperature due to changes in phonon-assisted relaxation processes, then the corresponding influence on the PL intensities would be opposite to the observed decrease with decreasing temperature. 49–52 While we cannot eliminate the possible influence of temperature dependent changes in non-radiative decay, we can conclude that the emissive properties of NAI-DMAC in solution are dominated by the molecular dynamics of the solvent and their influence on the structural dynamics of the emitter. Therefore, the slope of the line obtained from the ln(Int) versus 1/ T data in the 300 to 200 K range is dominated by the temperature dependence of diffusive motion of mTHF and its influence on k R .…”

“…This marked reduction of PL intensity at lower temperature is counter to common temperature dependent emission behaviors that typically exhibit increased PL intensity at lower temperatures. [49][50][51][52] Such typical behavior arises from thermal occupation of low frequency vibrational modes that allow access to non-radiative relaxation pathways such as conical intersections, leading to lower intensity emission at elevated temperatures. 50,53 The observation here of lower PL intensity at lower temperature cannot be explained by this phonon-assisted non-radiative decay mechanism because it exhibits the opposite trend.…”

Revealing and Tuning the Photophysics of C=N Containing Photothermal Molecules: Excited State Dynamics Simulations

“…A total duration time of 400 fs was applied unless the S 1 –S 0 gap becomes ≤0.2 eV. Following the literature, such a very small S 1 –S 0 gap was taken as a sign of approaching a CI region, due to the typical drawbacks of TD-DFT in dealing with strong coupling regions, especially the CI [ 21 , 22 , 23 , 24 ]. The CI geometry was ascertained by the complete active space self-consistent field (CASSCF) method with the 6-31G(d) basis set [ 25 , 26 ].…”

Effect of temperature on the first excited state splitting energy of the impurity magneto acoustic polaron in monolayer graphene

“…Actually,, due to the nonpolar nature of graphene, the electron phonon coupling via the acoustic phonon is more important than that of electron optical phonon coupling, which is usually used for the investigations of energy level characteristics [29,30]. Chen et al provide a feasible method to study the properties of the excited state of graphene materials [31,32]. Kurzmann et al studied the properties of excited states in bilayer graphene quantum dot [33].…”