Design and Nonadiabatic Photoisomerization Dynamics Study of a Three-Stroke Light-Driven Molecular Rotary Motor

Abstract

Working cycle of conventional light-driven molecular rotary motors (LDMRMs), especially Feringa-type motors, usually have four steps, two photoisomerization steps, and two thermal helix inversion (THI) steps. THI steps hinder the ability of the motor to operate at lower temperatures and limit the rotation speed of LDMRMs. A three-stroke LDMRM, 2-(2,7-dimethyl-2,3-dihydro-1H-inden-1-ylidene)-1,2-dihydro-3H-pyrrol-3-one (DDIY), is proposed, which is capable of completing an unidirectional rotation by two photoisomerization steps and one thermal helix inversion step at room temperature. On the basis of trajectory surface-hopping simulation at the semi-empirical OM2/MRCI level, the EP→ZP and ZP→EM nonadiabatic photoisomerization dynamics of DDIY were systematically analyzed. Quantum yields of EP→ZP and ZP→EM photoisomerization of DDIY are ca. 34% and 18%, respectively. Both EP→ZP and ZP→EM photoisomerization processes occur on an ultrafast time scale (ca. 100–300 fs). This three-stroke LDMRM may stimulate further research for the development of new families of more efficient LDMRMs.

Effect of Temperature on Photoisomerization Dynamics of a Newly Designed Two-Stroke Light-Driven Molecular Rotary Motor

“…As can be seen in Table S3 , all CIs involve obvious pyramidalization at the C2 atom site. Similar pyramidalization of the carbon atom at the stator-axle linkage was also observed in other molecular rotary motors [ 13 , 25 , 34 , 54 ].…”

“…As we can see, after the S →S optical excitation of EP or ZP isomer, molecular motor DDPY rotates around the central C=C double bond in a counterclockwise direction, and relaxes to the S state through the S /S conical intersections (CIs), then it arrives at the metastable ZM or EM isomer. Motivated by our previous work [ 25 ] and Filatov’s work [ 22 ], due to the very low energy barriers from ZM to ZP and from EM to EP isomers, as shown in Table 1 , we can expect that the molecular motor DDPY may exceed the barriers in timescales of femtoseconds and arrive at more stable ZP or EP isomers without staying at the ZM or EM metastable isomer at room or even lower temperature. Thus, the molecular motor DDPY could complete a full 360 rotation by only two photoisomerization steps ( EP → ZP and ZP → EP ) at room or even lower temperature.…”

“…Thus, reducing the THI steps can not only improve the rotation speed but also enable LDMRM to operate at lower temperatures [ 6 , 19 , 20 ]. Some developments have been achieved on reducing the THI steps theoretically [ 21 , 22 , 23 , 24 , 25 ] and experimentally [ 15 , 26 ] in recent years.…”

“…A novel molecular motor in which the rotation is induced by the electric coupling of chromophores was suggested by Majumdar et al [ 24 ] recently, which was predicted to achieve unidirectional rotation on a subnanosecond time scale using the power of a single photon. A three-stroke LDMRM, 2-(2,7-dimethyl-2,3-dihydro-1Hinden-1-ylidene)-1,2-dihydro-3H-pyrro- l-3-one (DDIY), was proposed by our group [ 25 ] very recently, which is capable of completing a unidirectional rotation by two photoisomerization steps and one thermal helix inversion step at room temperature.…”

“…Designing a light-driven molecular motor with fewer operational steps based on synthesized molecular systems may be an effective way. Based on some easy-to-synthesize oxindole-based molecular motors studied by Roke et al [ 12 ] and Pooler et al [ 13 ] recently, by further reducing the steric hindrance in the fjord region of the LDMRM DDIY proposed in our previous work [ 25 ], a new two-stroke LDMRM, 2-(1,5-dimethyl-4,5-dihydrocyclopenta[b]pyrrol-6(1H)-ylidene)-1,2-dihydro-3H-pyrrol-3-one (DDPY), was designed, in which only two photoisomerization steps ( EP → ZP and ZP→EP ) are involved to complete a full 360 rotation. The photoinduced isomerization dynamics of this two-stroke LDMRM were systematically investigated with trajectory surface-hopping molecular dynamics at the semi-empirical OM2/MRCI level.…”