Ab initio molecular dynamics of thiophene: the interplay of internal conversion and intersystem crossing

Abstract

The fast and slow components of the relaxation of photoexcited thiophene have been investigated by means of SHARC (surface hopping including arbitrary couplings) molecular dynamics based on multiconfiguration electronic structure calculations. Triplet states are included to ascertain their role in the relaxation process. After thiophene is excited to the S state, ultrafast dynamics (τ = 96 fs) initiates a ring opening due to cleavage of a carbon sulfur bond and simultaneous ring puckering. This time constant is in agreement with previous experimental and theoretical studies. The subsequent dynamics of the open-ring structures is characterized by the interplay of internal conversion and intersystem crossing. For the open-ring structures, the S, S, T and T states are nearly degenerate and the spin-orbit couplings are large. The underlying potential energy surface is flat and long-lived open-ring structures in the singlet as well as in the triplet states are formed. Both the participation of triplet states and the shape of the energy surface explain the experimentally observed slow ring closure in the ground state.

A combined multi-reference pump-probe simulation method with application to XUV signatures of ultrafast methyl iodide photodissociation

“…The Surface Hopping including ARbitrary Couplings (SHARC) program [29][30][31] provides such a computational framework and has been applied in various systems. [32][33][34][35] However, we still lack the bridge between theoretical chemical dynamics simulations and pump-probe measurements based on XAS probes. In this work, we provide a methodology and a working example of simulated transient XUV/X-ray absorption spectroscopy (XAS) employing the current SHARC framework.…”

Theoretical Investigations on Mechanisms and Pathways of C2H5O2 with BrO Reaction in the Atmosphere

“…The complete active spaces (CAS) calculations with all valence electrons are unaffordable at present. It is noted that the intersystem crossing might be significant in some small organic molecules [ 34 , 35 ], therefore, more rigorous treatment of the singlet-triplet transition has to be reserved for further study.…”

Aggregation Induced Emission in the Tetraphenylthiophene Crystal: The Role of Triplet States

“…The mechanism is similar to the observed in thiophene and its derivatives in vacuum, which involves both S 1 minima: 1 ππ * and 1 πσ * . [49][50][51][52][53][54] In the first step, the molecule relaxes to the 1 ππ * minimum (0.72 eV below S 1 at the FC geometry). The C-S stretching modes, among the others, gain kinetic energy enabling the C-S elongation and ring-opening (Figure 4).…”