title: Transient absorption spectroscopy on spiropyran monolayers using nanosecond pump-probe Brewster angle reflectometry.
abstract: Self-assembled monolayers of 11-(3',3'-dimethyl-6,8-dinitrospiro[chromene-2,2'-indoline]-1'-yl) undecanoic acid (amphiphilic spiropyran) at the air-water interface are studied using Brewster angle reflectometry. Transient kinetics of the spiropyran to merocyanine conversion are recorded in a UV-pump, VIS-probe configuration. By varying the probe wavelength using an optical parametric oscillator, we are able to reconstruct absorption spectra of intermediate states with a time-resolution of 10 nanoseconds, limited by the temporal convolution of the two laser pulses. After UV irradiation, spiropyran converts to merocyanine in two stages. The first occurs within a timescale of several tens of nanoseconds and is heavily convoluted with the system response time, whereas the second stage occurs over a few hundred nanoseconds. During the rise time there is a small red shift in the transient absorption spectrum of ~20 nm. We assign the red shift and the slower kinetics to the isomerization of a merocyanine isomer cis about the central methine bond to those that are trans about the same bond.
authors: Austrian Institute of Technology GmbH, AIT, BioSensor Technologies, Muthgasse 11, 1190 Vienna, Austria.
authors: Bernhard
authors: B
authors: Siebenhofer
authors: Sergey
authors: S
authors: Gorelik
authors: Martin J
authors: MJ
authors: Lear
authors: Hong Yan
authors: HY
authors: Song
authors: Christoph
authors: C
authors: Nowak
authors: Jonathan
authors: J
authors: Hobley
mesh_terms: D000388:Air; D001578:Benzopyrans / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry*; D007536:Isomerism; D007700:Kinetics; D008958:Models, Molecular; D009574:Nitro Compounds / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D001578:Benzopyrans; D007211:Indoles; D009574:Nitro Compounds; C548873:merocyanine; C088184:spiropyran; D014867:Water