Ultrafast dynamics of dithienylethenes differently linked to the surface of TiO2 nanoparticles

Modeling the Photochrome-TiO2 Interface with Bethe-Salpeter and Time-Dependent Density Functional Theory Methods

Hybrid organic-inorganic semiconductor systems have important applications in both molecular electronics and photoresponsive materials. The characterizations of the interface and of the electronic excited-states of these hybrid systems remain a challenge for state-of-the-art computational methods, as the systems of interest are large. In the present investigation, we present for the first time a many-body Green's function Bethe-Salpeter investigation of a series of photochromic molecules adsorbed onto TiO₂ nanoclusters. On the basis of these studies, the performance of time-dependent density functional theory (TD-DFT) calculations is assessed. In addition, the photochromic properties of different hybrid systems are also evaluated. This work shows that qualitatively different conclusions can be reached with TD-DFT relying on various exchange-correlation functionals for such organic-inorganic interfaces and paves the way to more accurate simulation of many hybrid materials.

Reversible Photomodulation of Electronic Communication in a π-Conjugated Photoswitch-Fluorophore Molecular Dyad

The extent of electronic coupling between a boron dipyrromethene (BODIPY) fluorophore and a diarylethene (DAE) photoswitch has been modulated in a covalently linked molecular dyad by irradiation with either UV or visible light. In the open isomer, both moieties can be regarded as individual chromophores, while in the closed form the lowest electronic (S0 →S1 ) transition of the dyad is slightly shifted, enabling photomodulation of its fluorescence. Transient spectroscopy confirms that the dyad behaves dramatically different in the two switching states: while in the open isomer it resembles an undisturbed BODIPY fluorophore, in the closed isomer no fluorescence occurs and instead a red-shifted DAE behavior prevails.

Vibrational coherence transfer in an electronically decoupled molecular dyad

The ring opening of a dithienylethene photoswitch incorporated in a bridged boron-dipyrromethene - dithienylethene molecular dyad was investigated with ultrafast spectroscopy. Coherent vibrations in the electronic ground state of the boron-dipyrromethene are triggered after selective photoexcitation of the closed dithienylethene indicating vibrational coupling although the two moieties are electronically isolated. A distribution of short-lived modes and a long-lived mode at 143 cm(-1) are observed. Analysis of the theoretical frequency spectrum indicates two modes at 97 cm(-1) and 147 cm(-1) which strongly modulate the electronic transition energy. Both modes exhibit a characteristic displacement of the bridge suggesting that the mechanical momentum of the initial geometry change after photoexcitation of the dithienylethene is transduced to the boron-dipyrromethene. The relaxation to the dithienylethene electronic ground state is accompanied by significant heat dissipation into the surrounding medium. In the investigated dyad, the boron-dipyrromethene acts as probe for the ultrafast photophysical processes in the dithienylethene.