Study On Hot-band Excitation,Triplet Sensitization And Low-powered Upconversion Based On Porphyrin Complexes

The typical triplet sensitizer Pd(II)octaethylporphyrin(Pd OEP)was first found to possess absorption involving the vibrational energy level(i.e.,hot-band)of the ground state,which results in the one-photon absorption(OPA)upconversion emission.Thus,combination of molecular hot vibrational energy-level absorption(one-photon hot-band absorption,OPA)and triplet-triplet-annihilation(TTA)was successfully conducted to obtain blue upconversion from 9,10-diphenylanthracene(DPA)under the excitation of655 nm diode laser,with anti-Stokes shift of 0.99 e V and the highest red-to-blue efficiency of 2.46%.Cascading one-photon hot-band absorption(OPA)and triplettriplet annihilation upconversion(TTA-UC)provides a novel low-powered upconversion approach that can effectively enhance the anti-Stokes shift in a simple way.Through multi-wavelength excitation(i.e.,532 nm,635 nm,655 nm till to 671 nm)of the upper vibration energy-levels on the ground state of sensitizer Pt(II)octaethylporphyrin(Pt OEP),the green-/yellow-/red-to-blue upconversion from DPA was firstly reported,which not only effectively increases anti-Stokes shift as large as 1.04 e V,but also achieves the multi-wavelength excitation,suggesting that there are potential application in the solar energy.The upconversion intensity decreases as the excitation wavelength is extended from 532 nm to 671 nm,indicating that the zerovibrational level excitation is much larger than the hot-vibrational level excitation.The importance in this study would enhance the hot band absorption by investigating new ways.If that takes off,it could lift the TTA-UC to a new level.Also applied the multi-wavelength excitation strategy,the TTA-UC was firstly obtained in the solid powders.Under multi-wavelength excitation(635 nm,655 nm,671 nm and 785 nm)of the upper vibration energy-levels on the groud state of sensitizer Pt-tetraphenyltetrabenzoporphyrin(Pt PTBT),the change in upconversion properties from solution to solid state after compounding 9,10-bis(phenylethynyl)anthracene(BPEA)and DPA with aggregate-induced emission.It was found that only if the sensitizer matches the energy level of the annihilator triplet state,it can be excited by hot-band.The annihilator triplet state energy levels can be tuned by solid state,thus realizing multi-wavelength hot-band excitation of solid-state materials.