CASSCF and MS-CASPT2 Studies on an Electron-tunable,1,2-Dicyanoethylene-based Optical Molecular Switch†

doi:10.7503/cjcu20150966

Abstract

Abstract:

CASSCF and MS-CASPT2 mechanistic studies were carried on the cis-trans isomerization processes of 1,2-dicyanoethylene in its neutral, cationic and anionic forms. The results confirmed the importance of electron-induction in reducing the reaction barrier, and more importantly, revealed the different nonadiabatic channels tuned by electron attachment/detachment. The S₁→S₀ decay of neutral dicyanoethylene need overcome a mild barrier(≥19.7 kJ/mol) to reach a H-migration-type, namely the S₁/S₀-CI, which is away from the C═C torsional coordinates and may slow down the speed of C═C rotation and hurt its directionality; while in cationic and anionic isomerization processes, the D₁ and D₀ PESs intersect along the rotary path, therefore, the nonadiabatic D₁→D₀ decay is barrierless, as result, the directionality of C═C rotation is maintained. The study revealed the role of electron induction in tuning the cis-trans photoisomerization, and shed light on the design of light-driven molecular rotary motors.

Key words: Cis-trans isomerization, Conical intersection, 1, 2-Dicyanoethylene, Molecular switch

CLC Number:

O641

TrendMD:

CAO Dan, LI Yuanying, SU Qingqing, WANG Bin, LIU Fengyi, WANG Wenliang. CASSCF and MS-CASPT2 Studies on an Electron-tunable,1,2-Dicyanoethylene-based Optical Molecular Switch^†[J]. Chem. J. Chinese Universities, 2016, 37(6): 1128.

Figures/Tables 7

Fig.1 Cis-trans isomerization reaction between maleonitrile(cis) and fumaronitrile(trans)

Fig.2 Nature of frontier MOs for cis and trans(A) and representative electronic configurations of ground- and excited states of neutral, cationic and anionic dicyanoethylene(B)

Fig.3 Nature of frontier MOs for cis(A) and trans(C) conformations and variation of MO energies along C1═C1' rotary path(B)a,a'. Anion; b,b'. neutral; c,c'. cation. a—c. MO 20; a'—c'. MO 21.

Fig.4 CASSCF(A), MS-CASPT2//CASSCF(B) and MS-CASPT2(C) computed PESs(potential energy surfaces) of 1,2-dicyanoethylene along rotary path(θ)a. S0-MEP; b. S0//S1; c. S1-MEP; d. S1//S0. The S1//S0 energy profiles indicate the S1-state energies on the basis of optimized S0-state structure(So does S0//S1 curves).

Fig.5 CASSCF-optimized geometry of S1/S0-CI(A) and MS-CASPT2//CASSCF intrapolated S1-min→S1/S0-CI MEP(B, dimensionless) of neutral dicyanoethylene

Fig.6 CASSCF computed PESs for cation(A) and anion(B) dicyanoethylene and the corresponding MS-CASPT2//CASSCF energy profiles for cationic(C) and anionic(D) dicyanoethylene along rotary path(θ)a. D0-MEP; b. D0//D1; c. D1-MEP; d. D1//D0.

Fig.7 Cationic(A1, A2) and anionic(B1, B2) D1-min(A1, B1) and D1/D0-CIs(A2, B2) optimized at the CASSCF/cc-pVTZ level

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