Ultrafast ring-opening and solvent-dependent product relaxation of photochromic spironaphthopyran. Issue 33 (12th August 2019)

• Record Type: Journal Article
• Authors: Bittmann, Simon F.; Dsouza, Raison; Siddiqui, Khalid M.; Hayes, Stuart A.; Rossos, Andreas; Corthey, Gastón; Kochman, Michał; Prokhorenko, Valentyn I.; Murphy, R. Scott; Schwoerer, Heinrich; Miller, R. J. Dwayne
• Is Part Of: Physical chemistry chemical physics. Volume 21:Issue 33(2019)
• Page Start: 18119
• Page End: 18127
• Publication Date: 2019-08-12
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c9cp02950h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Combined experiment and theory shed light on the dominant pathways involved in the photochemical reaction of spiropyran. Abstract : The ultrafast dynamics of unsubstituted spironaphthopyran (SNP) were investigated using femtosecond transient UV and visible absorption spectroscopy in three different solvents and by semi-classical nuclear dynamics simulations. The primary ring-opening of the pyran unit was found to occur in 300 fs yielding a non-planar intermediate in the first singlet excited state (S1 ). Subsequent planarisation and relaxation to the product ground state proceed through barrier crossing on the S1 potential energy surface (PES) and take place within 1.1 ps after excitation. Simulations show that more than 90% of the trajectories involving C–O bond elongation lead to the planar, open-ring product, while relaxation back to the S0 of the closed-ring form is accompanied by C–N elongation. All ensuing spectral dynamics are ascribed to vibrational relaxation and thermalisation of the product with a time constant of 13 ps. The latter shows dependency on characteristics of the solvent with solvent relaxation kinetics playing a role.