Photo-deactivation pathways of a double H-bonded photochromic Schiff base investigated by combined theoretical calculations and experimental time-resolved studies

Carlos Randino, Marcin Ziółek, Ricard Gelabert, Juan Angel Organero, Michal Gil, Miquel Moreno, José M. Lluch, Abderrazzak Douhal

Research output: Contribution to journalArticleResearchpeer-review

41 Citations (Scopus)

Abstract

The photophysics of N,N′-bis(salicylidene)-p-phenylenediamine (BSP) is analyzed both theoretically and experimentally. The alternative intramolecular proton-transfer reactions lead to three different tautomers. We performed DFT and TDDFT calculations to analyze the topography of the reactions connecting the three tautomers. Deactivation paths through a Conical Intersection (CI) region are also analyzed to explain the low fluorescence quantum yield of the phototautomers. The complex molecular structure of BSP provides a large number of deactivation paths, almost all of them energetically available following the initial photoexcitation. Femtosecond (fs) time-resolved emission studies in solution and flash photolysis experiments (nano to millisecond regime) were performed to get detailed information on the time domain of the full photocycle. The picture that emerges by combining theoretical and experimental results shows a very fast (less than 100 fs) photoinduced single proton transfer process leading to a phototautomer where a single proton has moved. This species may deactivate through a low-energy CI leading in about 20 ps to a rotameric form in the ground state that has a lifetime of several tens of microseconds in solution. This process competes with another deactivation path taking place prior to the proton-transfer reaction which involves a low-energy CI leading to a rotamer of the enol structure. In the flash photolysis studies, the rotamer of the enol structure was directly identified by the positive transient absorption band in the 250-260 nm and its lifetime in n-hexane (10 ms) is almost 3 orders of magnitude longer than the lifetime of the photochrome (around 40 μs). Our findings do not exclude a double proton transfer reaction in the excited enol form to give a tautomer in less than 100 fs during the first (impulsive) phase of the reaction which reverts back to the photoproducts of the simple proton transfer in 1-3 ps. © 2011 The Owner Societies.
Original languageEnglish
Pages (from-to)14960-14972
JournalPhysical Chemistry Chemical Physics
Volume13
Issue number33
DOIs
Publication statusPublished - 7 Sep 2011

Fingerprint Dive into the research topics of 'Photo-deactivation pathways of a double H-bonded photochromic Schiff base investigated by combined theoretical calculations and experimental time-resolved studies'. Together they form a unique fingerprint.

Cite this