Abstract
Triplet-triplet annihilation based molecular photon upconversion (TTA-UC) is an exciting research area for a broad range of photonic applications due to its tunable spectral range and possible operation at non-coherent solar irradiance. Most of the TTA-UC studies are limited to Visible to Visible (Vis to Vis) energy upconversion. However, for several practical photonic applications, efficient near infrared (NIR) to Vis upconversion is preferred. Examples include, (i) photovoltaics where TTA-UC could lead to utilization of a larger part of the solar spectrum and (ii) in NIR stimulated biological applications where the deep penetration and non-invasive nature of NIR light coupled to TTA-UC offers new opportunities. Although, NIR to Vis TTA-UC is known since 2007, the recent five years have witnessed quite a progress in terms of the development of new chromophores, hybrid systems and fabrication techniques to increase the UC quantum yield at low excitation intensity. With this tutorial review we are reviewing recent progress, identifying existing challenges and discus possible future directions and opportunities.
Highlights
Among the emerging artificial light harvesting systems, molecular photon upconversion operating via triplet–triplet annihilation (TTA-UC) is investigated for various photonic applications including photovoltaics, bioimaging, photocatalysis, photodynamic therapy, sensing and optogenetics.[1,2,3,4,5,6]
TTA-UC is a photochemical phenomenon wherein low energy photons are converted to high energy photons via a series of energy transfer processes between chromophores.[7]
A typical TTA-UC system is an ensemble of annihilator chromophores doped with triplet sensitizer, wherein after excitation at low energy, the sensitizer transfers its triplet energy to the annihilator, followed by annihilation of two sensitized annihilator triplets, leading to anti-Stokes delayed fluorescence at higher
Summary
Among the emerging artificial light harvesting systems, molecular photon upconversion operating via triplet–triplet annihilation (TTA-UC) is investigated for various photonic applications including photovoltaics, bioimaging, photocatalysis, photodynamic therapy, sensing and optogenetics.[1,2,3,4,5,6] This is due to its operation at tunable wide spectral ranges and its function at low excitation intensities (B1 mW cmÀ2) of non-coherent light, corresponding to AM 1.5 solar irradiance intensities and below.[3]. The developments in NIR to Vis TTA-UC systems are mainly limited to deoxygenated organic solvents which leads to challenges for device fabrication and is not applicable for in vivo applications. On grounds of the promising applications offered by NIR light, it is imperative to understand the underlying reasons at the mechanistic level leading to low UC quantum yield of these systems In this tutorial review we are reviewing the developments in NIR to Vis TTA-UC systems in terms of new chromophores, sensitization, energy transfer mechanisms, hybrid systems and fabrication techniques to increase the UC quantum yield at low excitation intensity. Existing challenges and future directions are discussed as guiding path for further research
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
