title: Insights from Theory and Experiment on the Photochromic spiro-Dihydropyrrolo-Pyridazine/Betaine System.
abstract: We elucidated the photochromic spiro-4a,5-dihydropyrrolo[1,2-b]pyridazine/betaine (DPP/betaine) system by comparing state-of-the-art density functional theory calculations with nanosecond/millisecond UV-vis absorption spectroscopy, as well as steady-state absorption and cyclization kinetics. Time-dependent density functional theory calculations are employed to examine the transformations occurring after photoexcitation. This study shows that the photochromic spiro-4a,5-dihydropyrrolo[1,2-b]pyridazine and spiro-1,8a-dihydroindolizine (DHI) systems react according to similar pathways. However, notable differences exist. Although photoexcitation of the spiro-DPP system also leads to cis-betaines, which then isomerize to trans-betaines, we found two distinct classes of cis isomers (cis-betaine rotamer-1 and cis-betaine rotamer-2), which do not exist in spiro-1,8a-dihydroindolizine. Similar to our previous study on the spiro-DHI/betaine system, a complicated potential-energy landscape between cis and trans isomers exists in the spiro-DPP system, consisting of a network of transition states and intermediates. Because the spiro-DPP/betaine is even more complicated than the spiro-DHI/betaine system, (substituted) photochromic systems featuring a 4a,5-dihydropyrrolo[1,2-b]pyridazine functional unit will require thorough in silico design to function properly as logical gates or in devices for information storage.
authors.affiliation: Department of Chemistry, Kansas State University , 213 CB Building, 1212 Mid-Campus Drive North, Manhattan, Kansas 66506, United States.
authors.forename: Amendra
authors.initials: A
authors.lastname: Fernando
authors.affiliation: Department of Chemistry, Kansas State University , 213 CB Building, 1212 Mid-Campus Drive North, Manhattan, Kansas 66506, United States.|Department of Anatomy & Physiology, Kansas State University , Coles Hall 228, 1600 Denison Avenue, Manhattan, Kansas 66506, United States.
authors.forename: Tej B
authors.initials: TB
authors.lastname: Shrestha
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , 100 W. 18th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Yao
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Kansas State University , 213 CB Building, 1212 Mid-Campus Drive North, Manhattan, Kansas 66506, United States.
authors.forename: Aruni P
authors.initials: AP
authors.lastname: Malalasekera
authors.affiliation: Department of Chemistry, Kansas State University , 213 CB Building, 1212 Mid-Campus Drive North, Manhattan, Kansas 66506, United States.
authors.forename: Jing
authors.initials: J
authors.lastname: Yu
authors.affiliation: Department of Chemistry, Kansas State University , 213 CB Building, 1212 Mid-Campus Drive North, Manhattan, Kansas 66506, United States.
authors.forename: Emily J
authors.initials: EJ
authors.lastname: McLaurin
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , 100 W. 18th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Claudia
authors.initials: C
authors.lastname: Turro
authors.affiliation: Department of Chemistry, Kansas State University , 213 CB Building, 1212 Mid-Campus Drive North, Manhattan, Kansas 66506, United States.
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Bossmann
authors.affiliation: Department of Chemistry, Kansas State University , 213 CB Building, 1212 Mid-Campus Drive North, Manhattan, Kansas 66506, United States.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Aikens