Photoisomerization of Stilbene: A Spin-Flip Density Functional Theory Approach

Abstract

The photoisomerization process of 1,2-diphenylethylene (stilbene) is investigated using the spin-flip density functional theory (SFDFT), which has recently been shown to be a promising approach for locating conical intersection (CI) points (Minezawa, N.; Gordon, M. S. J. Phys. Chem. A2009, 113, 12749). The SFDFT method gives valuable insight into twisted stilbene to which the linear response time-dependent DFT approach cannot be applied. In contrast to the previous SFDFT study of ethylene, a distinct twisted minimum is found for stilbene. The optimized structure has a sizable pyramidalization angle and strong ionic character, indicating that a purely twisted geometry is not a true minimum. In addition, the SFDFT approach can successfully locate two CI points: the twisted-pyramidalized CI that is similar to the ethylene counterpart and another CI that possibly lies on the cyclization pathway of cis-stilbene. The mechanisms of the cis-trans isomerization reaction are discussed on the basis of the two-dimensional potential energy surface along the twisting and pyramidalization angles. Disciplines Chemistry CommentsReprinted (adapted) with permission from

Assessment of approximate computational methods for conical intersections and branching plane vectors in organic molecules

“…In the domain of density functional theory (DFT), the use of the spinflip (SF) ansatz in the context of time-dependent DFT (SF-TDDFT) [14][15][16][17] allows the treatment of intersections between ground-and excited-state PESs. 18,19 An alternative approach based on ensemble DFT is the state-interaction state-averaged restricted ensemble-referenced Kohn-Sham (SI-SA-REKS) method, which has also been shown to be suited for describing CIs in organic molecules. 20 Both these DFT-based methods have been applied to optimize CIs and to determine BPs.…”

“…20 Both these DFT-based methods have been applied to optimize CIs and to determine BPs. [18][19][20][21][22][23] Semiempirical quantum-chemical methods 24,25 have become increasingly popular for investigating the non-adiabatic dynamics of excited states, in particular, the OM2/MRCI approach with an orthogonalization-corrected model Hamiltonian (OM2). 25,26 Taking advantage of its very low computational demands, numerous on-the-fly non-adiabatic molecular dynamics (MD) simulations have been performed with OM2/MRCI for electronically excited organic molecules.…”

Ab Initio Multiple Spawning Photochemical Dynamics of DMABN Using GPUs

“…[50][51][52] It has been suggested 50 that the spin-flip variants 53 of LR-TDDFT might solve this problem, and some promising results for S 0 /S 1 conical intersections have been obtained with this strategy. [54][55][56][57] Unfortunately, spin-flip LR-TDDFT often leads to severe spin contamination, which has been a stumbling block to widespread use.…”

Stilbene photoisomerization driving force as revealed by the topology of the electron density and QTAIM properties

“…This degree of freedom was varied from 0.0°to 180.0°in increments ranging from 1°to 15°. Since the use of LR-TDDFT is questionable for the proper location of CIs, [23] we used the spin-flip time-dependent density functional theory (SF-TDDFT) 1 twisted-pyramilized conical intersection of stilbene [24] to start the construction of the potential energy curves of this work. Based on the structure of this CI, LR-TDDFT vertical excitation energies plotted in Fig.…”