%0 Journal Article %A Mohammed, Omar F. %A Ahmed, Saleh A. %A Vauthey, Eric %A Nibbering, Erik T.J. %T Photoinduced Ring-Opening of a Photochromic Dihydroindolizine Derivative Monitored with Femtosecond Visible and Infrared Spectroscopy %J Journal of Physical Chemistry A %@ 1089-5639 %V 113 %N 17 %P 5061-5065 %D 2009 %U http://pubs.acs.org/doi/abs/10.1021/jp811248u %R 10.1021/jp811248u %U http://archive-ouverte.unige.ch/unige:3547 %X We present results of a femtosecond spectroscopy study of the ring-opening dynamics of the photochromiccompound trimethyl-1′H-spiro[fluorene-9,1′-pyrrolo[1,2-b]pyridazines]-2′,3′,6′-tricarboxylate (also known asdihydroindolizine and abbreviated as DHI) in solvents of different polarities. We follow the ring-openingdynamics of photoexcited DHI by probing the transient response in the visible region between 450 and 700nm, as well as in the fingerprint region between 1100 and 1800 cm-1. We conclude that photoexcited DHIconverts into the ring-opened betaine isomer while remaining in the electronic excited state. Subsequentelectronic excited-state decay on a time scale of 40-80 ps results in regeneration of ground-state DHI (0.75-0.9quantum yield) or betaine photoproduct, the exact value for DHI quantum yield recoveries and rates beingsolvent dependent. Figure Steady state of DHI in ACN-d3, DCM-d2, and TCE (A).Transient spectra of DHI at different pulse delays after 400 nm laserexcitation in ACN-d3 (B), in DCM-d2 (C), and in TCE (D).