Efficient Solid-State Photon Upconversion Enabled by Spin Inversion at Organic Semiconductor Interface

We realized solid-state UC with 100 times higher efficiency than a conventional system by discovering a novel UC mechanism in bilayer organic semiconductor heterojunctions. The UC occurred through spin inversion during the charge separation and recombination at the interface. The key to the success was the triplet formation at the interface, as this could avoid the loss process during triplet diffusion, which is a problematic issue in conventional systems. As a result of this finding, efficient UC from near-infrared to visible light on flexible thin films under LED light excitation was made possible.

Efficient Solid-State Photon Upconversion Enabled by Spin Inversion at Organic Semiconductor Interface

We realized solid-state UC with 100 times higher efficiency than a conventional system by discovering a novel UC mechanism in bilayer organic semiconductor heterojunctions. The UC occurred through spin inversion during the charge separation and recombination at the interface. The key to the success was the triplet formation at the interface, as this could avoid the loss process during triplet diffusion, which is a problematic issue in conventional systems. As a result of this finding, efficient UC from near-infrared to visible light on flexible thin films under LED light excitation was made possible.

Ultrafast spectroscopy reveals singlet fission, ionization and excimer formation in perylene film

Singlet exciton fission (SF) is a spin-allowed process whereby two triplet excitons are created from one singlet exciton. This phenomenon can offset UV photon energy losses and enhance the overall efficiency in photovoltaic devices. For this purpose, it requires photostable commercially available SF materials. Excited state dynamics in pure perylene film, ease of commercial production, is studied by time-resolved fluorescence and femtosecond transient absorption techniques under different photoexcitation energies. In film, polycrystalline regions contain perylene in H-type aggregate form. SF takes place from higher excited states of these aggregates in ultrafast time scale < 30 fs, reaching a triplet formation quantum yield of 108%. Moreover, at λex = 450 nm singlet fission was detected as a result of two-quantum absorption. Other competing relaxation channels are excimer (1 ps) and dimer radical cation formation (< 30 fs). Excimer radiatively relaxes within 19 ns and radical cation recombines in 3.2 ns. Besides, exciton self-trapping by crystal lattice distortions occurs within hundreds of picosecond. Our results highlight potential of simple-fabricated perylene films with similar properties as high-cost single crystal in SF based photovoltaic applications.

Extremely fast triplet formation by charge recombination in a Nile Red/fullerene flexible dyad

Fast and efficient triplet formation via charge separation followed by radical pair intersystem crossing is reported in a calixarene-based donor/acceptor dyad.

Theoretical and Experimental Investigation on the Intersystem Crossing Kinetics in Benzothioxanthene Imide Luminophores, and Their Dependence on Substituents Effects

<p><i>In spite of their remarkable luminescence properties, benzothioxanthene imide (BTXI an imide containing rylene chromophores) derivatives have been largely overlooked compared to their perylene bisimide and naphthalene bisimide counterparts. Thus their detailed photophysics are much less understood. In this paper, we show how relatively simple structural modifications of the backbone of BTXIs can lead to impressive variations in their Inter-System Crossing kinetics. Thus, through rational engineering of their structure, it is possible to obtain a triplet formation quantum yield that reaches unity, making BTXI a promising class of compounds for triplet-based applications (photodynamic therapy, electroluminescence, etc.).</i></p>

Theoretical and Experimental Investigation on the Intersystem Crossing Kinetics in Benzothioxanthene Imide Luminophores, and Their Dependence on Substituents Effects

<p><i>In spite of their remarkable luminescence properties, benzothioxanthene imide (BTXI an imide containing rylene chromophores) derivatives have been largely overlooked compared to their perylene bisimide and naphthalene bisimide counterparts. Thus their detailed photophysics are much less understood. In this paper, we show how relatively simple structural modifications of the backbone of BTXIs can lead to impressive variations in their Inter-System Crossing kinetics. Thus, through rational engineering of their structure, it is possible to obtain a triplet formation quantum yield that reaches unity, making BTXI a promising class of compounds for triplet-based applications (photodynamic therapy, electroluminescence, etc.).</i></p>