Theoretical characterization of a multifunctional electrooptical molecular device: Photochemical ring-opening mechanism of indolinospirobenzopyran

✍ Scribed by Anders Broo

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 308 KB
• Volume: 77
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(2000)77:1<454::aid-qua45>3.0.co;2-f

✦ Synopsis

Geometries of the spiro form SP and the merocyanine form MC of Ž . 1,3,3-trimethylspiro 2H-1-benzopyran-2,2Ј-indole and the 6Ј-nitro-substituted analog were calculated at the AM1, HFr3-21G, and B3LYPr3-21G levels of theory. The geometry of the lowest excited state of both forms was calculated utilizing the CISr3-21G method. The ring-opening mechanism and the spectroscopy of both systems were investigated. The earlier proposed mechanisms, based on time-resolved transient absorption spectroscopy, were confirmed in most details. The low-lying n ª * state of the 6Ј-nitro-substituted spiropyran, absent in the unsubstituted spiropyran, causes the rather different photochemical behavior of the two systems. The proximity of the first n ª * state and the low-energy ª * state opens up an exit channel to the triplet manifold, which complicates the mechanism. Solvent effects play an important role for the formation of the final merocyanine product for the 6Ј-nitro-substituted spiropyran. A new interpretation of the observed transient absorption spectrum of SP-H and new assignments of some of the peaks if the MC-NO spectrum are proposed.