Theoretical Studies of the Ground and Excited State Structures of Stilbene
journal contributionposted on 03.10.2013, 00:00 by Rajat K. Chaudhuri, Karl F. Freed, Sudip Chattopadhyay, Uttam Sinha Mahapatra
Optimized geometries are evaluated for the ground and low lying excited states of cis-stilbene, trans-stilbene, and 4a,4b-dihydrophenanthrene (DHP) from calculations performed with the improved virtual orbital, complete active space configuration interaction (IVO-CASCI) method. The calculations indicate that a nonplanar conformer of trans-stilbene is the most stable among the isomers. The calculated ground and low lying excited state geometries agree well with experiment and with prior theoretical estimates where available. Our IVO-CASCI based multireference Möller–Plesset (MRMP) computations place the 1Bu state of trans stilbene to be ∼4.0 eV above the ground X1Ag state, which is in accord with experiment and with earlier theoretical estimates. The 11Bu state of trans-stilbene can be represented by the highest occupied molecular orbital (HOMO) → lowest unoccupied molecular orbital (LUMO) transition (ionic type) from the ground state, whereas its 21Bu state is dominated by the HOMO → LUMO+1 and HOMO-1 → LUMO transitions (covalent type). Likewise, the 11B and 21B states of cis-stilbene and DHP are also found to be of ionic and covalent types, respectively.