Beating maps of singlet fission: Simulation of coherent two-dimensional electronic spectroscopy by Davydov ansatz in organic molecules

Abstract

The coherent two-dimensional (2D) electronic spectra for both the intra- and inter-molecular singlet fission (SF) processes in organic molecules are simulated by the Davydov ansatz combined with the Frenkel-Dirac time-dependent variational algorithm. By virtue of the dynamical approach, we are able to identify the signals of triplet excitation in the excited-state absorption contribution of the 2D spectra. In order to discuss whether a mediative charge-transfer (CT) state is necessary to SF, we increase the CT-state energy and find, in a theoretical manner, that the beating signal related to the triplet is inhibited. The vibronic coherence is then studied in the beating maps for both the ground and excited states. Except for the normal beating modes adhering to the relevant electronic state, we observe signals that are explicitly related to the triplet excitations. The pathways of transition corresponding to these signals are clarified in the respective Feynman diagram, which can help the experimenters determine the physical origin of relevant measurements.

Temperature effects on singlet fission dynamics mediated by a conical intersection

“…The so-defined bath does not affect electronic population relaxation ([HS, HSB] = 0) but induces the dephasing of coherences between the electronic states |g⟩ and |S 1 ⟩, |TT⟩. 34,35 Then, the total third-order response functions describing spectroscopic signals of the SF system are expressed as products of the system and the bath response functions, where the bath response functions are evaluated analytically through the line shape functions of the Brownian oscillator model (see Appendix B).…”

“…31,32 In the past decade, a method has been developed, which enables efficient, accurate simulation of optical responses of multimode systems with CIs through the evaluation of the third-order response functions within the framework of the Dirac-Frenkel timedependent variation combined with a hierarchy of the multiple Davydov Ansätze. 9,[33][34][35][36] On the one hand, this method performs well in grasping nonadiabatic dynamics at CIs. On the other hand, it is flexible and offers a good balance between the accuracy and efficiency by varying the multiplicity of the Davydov trial states.…”

Monitoring of singlet fission via two-dimensional photon-echo and transient-absorption spectroscopy: Simulations by multiple Davydov trial states

“…40,41 2D electronic spectra have been simulated with respect to SF by the single Davydov D 1 Ansatz. 42 It should be mentioned that the time-dependent Davydov Ansätze and their multiple extensions were developed and shown to represent an accurate, efficient method for the simulation of electron-vibrational quantum dynamics at CIs with many degrees of freedom (DOFs). This method performs excellently for both the diabatic wave-packet dynamics and the adiabatic ones at multimode CIs.…”

Ultrafast dynamics in rubrene and its spectroscopic manifestation

“…The singlet fission and geminate triplet fusion rates of rubrene have been extracted recently from timeresolved photoluminescence (TRPL) spectroscopy [7][8][9]. The spin-allowed singlet fission process converts a singlet state to a correlated triplet pair, pointing toward a promising pathway beyond the current organic photovoltaics efficiency limit [10,11]. Because singlet fission can raise the maximum ratio of incident photon to converted electron from 100% to 200% by creating two electron-hole pairs, organic molecules with fission property can be used to circumvent the long-standing Shockley-Queisser limit for solar energy conversion [10].…”