Singlet fission in thin films of metallo-supramolecular polymers with ditopic thiophene-bridged terpyridine ligands

Abstract

Ultrafast singlet exciton fission in thin solid films after UV laser photoexcitation was observed using transient absorption spectroscopy.

Singlet Fission in Thin Solid Films of Bis(thienyl)diketopyrrolopyrroles

“…The experimental setup was described in detail in our previous work. [37] Unless otherwise noted, the TA experiments were done with linearly polarized pump and probe laser beams with their polarization vectors making the angle α = 54.7°("magic angle") in order to eliminate effects of photoinduced anisotropy decay on the recorded kinetics. [38] This approach allowed us to use a polarization filter in the probe light collection optics placed between the sample and the photodetector, to reduce the artifacts caused by stray light from the pump beam.…”

“…Spectrally broadband (white‐light continuum) probe pulses were derived from Ti:sapphire laser pulses by means of a CaF 2 single crystal. The experimental setup was described in detail in our previous work [37] . Unless otherwise noted, the TA experiments were done with linearly polarized pump and probe laser beams with their polarization vectors making the angle α=54.7° (“magic angle”) in order to eliminate effects of photoinduced anisotropy decay on the recorded kinetics [38] .…”

Kinetics of the Photoexcited States in Thin Films of Metallo-Supramolecular Polymers With Ditopic Thiophene-Bridged Terpyridine Ligands

“…MSPs containing π-conjugated building blocks gained interest as materials for optoelectronic devices, covering light to electricity conversion, and for polymer light-emitting diodes (PLEDs) ( Hissler, 2019 ). Recent finding of an efficient singlet fission process in thin films of MSP based on α,ω−bis(tpy)terthiophene unimers assembled with Zn 2+ ion couplers ( Rais et al, 2017b ) shows that some MSPs could also be potentially exploited for better light harvesting in photovoltaics. The supramolecular approach to polymer chemistry evidently meets the actual needs of new functional materials for advanced electronics.…”

“…Relaxation processes running in photoexcited molecules of these unimers and MSPs were identified and characterized, and the impact of disturbed coplanarity of adjacent rings (dihedral angles between planes of rings due to the attached hexyl side groups) on these processes was shown ( Rais et al, 2015 ). Two different physical processes were found in thin films of PT depending on the excitation wavelength ( Rais et al, 2017b ). Using the wavelength 332 nm, the system showed a fast singlet fission (SF) process with a time constant .…”

“…These triplet excitations also proved power-law decay. Although the evolution of singlet and triplet exciton populations was experimentally well-characterized in the study by Rais et al, (2017b ), the origin of the bi-molecular singlet annihilation and subsequent triplet formation and decay remained unexplained. Meanwhile, we have elaborated a novel mathematical technique ( Menšík et al, 2018a ; Rais et al, 2018 ; Menšík et al, 2019 ), which makes the determination of the time-resolved diffusion coefficient from the transient absorption kinetics of photoexcited species possible.…”