Effects of metal free side chain on the optical properties of the probe for hydrogen peroxide detecting and responsive mechanism

Optical properties and responsive mechanisms of the two fluorescent probes Mol1 and Mol2 for Hydrogen peroxide (H2O2) are investigated by using time-dependent density functional theory. The result shows that the absorption and emission wavelengths of the probe Mol2 appear red shift comparing with the probe Mol1, which is due to the influence of the two side chains of the probe Mol2. The Mol2 has better probing properties. Moreover, responsive mechanisms of the probes are studied by analyzing the distributions of molecular orbitals and charge transfer, which are shown as the photon-induced electron transfer (PET) for them. Specially, the energy gaps of the two product molecules are calculated with optimal Hartree-Fock (OHF) method. We find that the S-T energy gap (ΔEst) of the product of probe Mol2 is 0.31 eV, which is narrower than 0.39 eV of the product of probe Mol1. Also, it is less than 0.42 eV which is the generation threshold of delayed fluorescence. From the computational results, one can see that the probe Mol2 is a thermally activated delayed fluorescence (TADF) probe that has excellent performance, according to the probing behavior. Our computational results have a guiding significance for further experimental works.