fs transient spectroscopy of TBA-KMoSn[BOD] in MeCN

Transient absorption spectroscopy was performed on acetonitrile solution samples of the bodipy hybrid TBA-KMoSn[BOD] with an OD 0.25 to 0.9 AU, in a 1 mm pathlength quartz cuvette. The samples were purged with N₂ before each measurement. The transient absorption setup was based on an amplified Ti:sapphire laser (Mai-Tai, Spitfire; both Spectra Physics) providing 80 fs pulses at 800 nm at the rate of 1 kHz. The pulses were split into two beams: excitation pulses (525 nm) were generated by optical parametric amplifier OPA (TOPAS C), Light Conversion) and probe pulses (white light supercontinuum) were generated by a CaF₂ crystal. The excitation and delayed probe beams were set to overlap in the sample (1 mm quartz cuvette). Consequently, the probe beam was dispersed on a photodiode array coupled to a spectrograph (Pascher Instruments). The transient absorption signal was calculated from a difference between spectra of two consecutive probe pulses passing though excited and unexcited sample, respectively. This was maintained by an optical chopper running at a frequency of 500 Hz which was synchronized with the laser. The angle between polarizations of excitation and probe beam were set to the so-called magic angle (54.7 degrees) to avoid observation of dynamics connected to transition dipole rotation. The excitation intensity used was 650 μW, corresponding to 1.3 nJ per pulse.