Abstract
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.
Highlights
The ring opening of a dithienylethene photoswitch incorporated in a bridged boron-dipyrromethene dithienylethene molecular dyad was investigated with ultrafast spectroscopy
The present study describes the ring opening dynamics of the molecular switch dithienylethene (DTE) which is covalently linked to a boron-dipyrromethene (BODIPY) via a molecular bridge
While the electronic excitation is strictly located on the DTE and the bridge, the BODIPY acts as indicator for nuclear motions within the complete molecular dyad
Summary
The ring opening of a dithienylethene photoswitch incorporated in a bridged boron-dipyrromethene dithienylethene molecular dyad was investigated with ultrafast spectroscopy. Analysis of the theoretical frequency spectrum indicates two modes at 97 cm[21] and 147 cm[21] 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 development of femtosecond time resolved spectroscopy with pulses shorter than the period of molecular vibrations has opened a way to monitor coherent vibrational wavepackets in the electronic ground and excited states and added decisive information about the primary processes on the excited and ground state potential energy surfaces of various systems In this context the correlation between the initial nuclear motion out of the Franck-Condon region and the photochemical reaction is a central issue. Derivative-like transient absorption features at the spectral position of the BODIPY ground state absorption indicate that the fast relaxation to the molecular electronic ground state is accompanied by significant heating of the surrounding medium
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