Oligo(phenylenevinylene)s with Terminal Donor–Acceptor Substitution This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.

Ultrafast Photo-Dynamics of a Reversible Photochromic Spiropyran

We report the first ultrafast ring closure kinetics of the merocyanine (MC) of a reverse photochromic spiropyran 1‘,3‘,3‘-trimethyl-6,8-dinitrospiro[2H-1-benzopyran-2,2-indoline] (6,8-dinitro BIPS) and its 1‘-(2-carboxyethyl) substituted derivative. The reaction is fast and essentially over in a few hundred picoseconds. The rate of MC-S1 state decay evaluated from transient absorbance can be correlated directly with the MC-S1 state lifetime as determined using stimulated and ordinary emission measurements. The recovery of the MC-S0 state from MC-S1 has a component with a lifetime of 60−78 ps in acetonitrile with a second component of 350−470 ps probably due to a metastable intermediate. We …

Ground- and First-Excited-Singlet-State Electric Dipole Moments of Some Photochromic Spirobenzopyrans in Their Spiropyran and Merocyanine Form

The dipole moments of four photochromic derivatives of indolinospirobenzopyran have been studied in their spiro and their open merocyanine form, in dioxane. Determinations have been done by electrooptical absorption measurements (EOAM). To prepare either a pure spiropyran or a pure merocyanine form solution, the experimental setup had to be modified by addition of a second light beam. In this way thermal equilibration between the spiropyran and the merocyanine form and switching from one form to the other induced by the measuring light beam could be avoided. The ground-state dipole moment of the spiro form amounts to (10−15) × 10-30 C m and increases strongly to about 60 × 10-30 C m with th…

Oligo(phenylenvinylene) mit terminaler Donor-Acceptor-Substitution

Heterocyclic systems containing tin(IV)—XIII [1]. Possible ceasing or inversion of the structuraltrans influence during the course of a bimolecular nucleophilic attack of a donor group in a series of SnIV rings

Abstract In the series of the heterocycles X[(CH2)3]2SnR2 (16 newly synthesized compounds and two taken from the literature) and in the germanium analog BuiN[(CH2)3]2GeCl2, the donor group X (= NMe, NBz, NBui, NPri, O, S) intramolecularly attacks the Lewis acidic atoms Sn or Ge. Eight structure determinations (and, in addition, 2 taken from the literature) are compared. The nucleophilic attack at Sn is stronger for the ligands R2 =Cl2 than for the more electronegative R2 = (OSiPh3)2. Overall the familiartrans influence holds: simultaneous approach of X and weakening of the ligand R (trans). In three cases of subtly graded donor strength a slight inversion or ceasing is observed: shorter dis…