Tsz Sian Chwee

Modelling fluorescence lifetimes with TD-DFT: a case study with syn-bimanes

Syn-bimanes are a class of fluorophores that are widely used for labelling thiol containing biological systems. We used time-dependent density functional theory (TD-DFT) with various hybrid exchange–correlation functionals (B3LYP, PBE0, M06, BMK, CAM-B3LYP, and M06-2X) within the adiabatic approximation to study various photophysical properties of syn-bimanes, such as the absorption and emission to and from the lowest optically bright state, solvatochromism, and fluorescence lifetimes. The mean unsigned errors (MUEs) for absorption with the hybrid functionals B3LYP, PBE0, and M06, were found to be around 0.1 eV, while errors for BMK and CAM-B3LYP were higher than 0.2 eV. With the exception of B3LYP, the MUEs for emission calculated using other functionals were less than 0.2 eV. PBE0 and M06 were found to yield the most accurate fluorescence lifetime results among the tested functionals, with MUEs under 2.0 ns.

Stable manganese carbonyl radicals as a rapid colorimetric thiol and hydrazine sensor

Blue cyclopentadienyl manganese dicarbonyl anilinyl radical complexes have been developed as a rapid and sensitive colorimetric thiol and hydrazine sensor with sensitivity limits approaching 3 ppm.

Computational modelling of singlet excitation energy transfer: a DFT/TD-DFT study of the ground and excited state properties of a syn bimane dimer system using non-empirically tuned range-separated functionals

The ground and excited state properties of a syn (H, H) bimane dimer was investigated using correlated wave function methods such as CCSD(T), EOM-CCSD, CR-EOM-CCSD(T) and DFT/TD-DFT with various exchange–correlation functionals (CAM-B3LYP, M06-2X, M11, ωB97X and ωB97XD). The ωB97X functional with a non-empirically tuned range-separation parameter, ωB97X*, was found to be the best performer with respect to studying the vertical excitation energies and interaction energies in the syn (H, H) bimane dimer. These results were applied to model the process of excitation energy transfer within a dimethylene bridged anti, syn bisbimane molecule. The rate of energy transfer was computed to be 2.6 × 1011 s−1, close to the experimental value of 6.7 × 1011 s−1.

Oxidation of aromatic alkenes and alkynes catalyzed by a hexa-acetonitrile iron(II) ionic complex [Fe(CH3CN)6][BF4]2

Oxidative cleavage of aromatic alkenes and oxidation of alkynes have been catalyzed by a simple Fe(II) complex [Fe(CH3CN)6][BF4]2 using H2O2 as an oxidant at room temperature. A free radical mechanism has been proposed involving the peroxy (OOH) radical to account for our experimental findings.

Computational study of molecular properties with dual basis sets

We have studied the performance of dual basis (DB) sets for the evaluation of molecular properties via second order Møller-Plesset perturbation theory (MP2). In addition to savings derived from using a trimmed basis set for the underlying Hartree-Fock (HF) calculation, we pursued a systematic truncation of the virtual subspace for further reductions in computational overhead during the post-HF step. Calculated total energies and molecular properties within the DB framework without virtual space truncation are generally in excellent agreement with full basis calculations. When aug-cc-pV5Z is used as the parent basis, mean absolute error for DB-HF (DB-MP2) total energies of molecules within our test set is 9.7 × 10(-5) au (8.0 × 10(-5) au) while mean absolute relative errors for static electrical response properties like dipole moments, isotropic dipole polarizabilities and polarizability anisotropies are 0.15% (0.14%), 0.56% (0.72%), and 0.76% (0.83%) respectively. When DB is coupled with virtual space truncation at the MP2 level, the corresponding errors are larger but still within 2% of full basis values.