posted on 2016-01-26, 00:00authored byAmendra Fernando, Tej B. Shrestha, Yao Liu, Aruni P. Malalasekera, Jing Yu, Emily J. McLaurin, Claudia Turro, Stefan H. Bossmann, Christine M. Aikens
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.