We have implemented and tested spin-flip timedependent density-functional theory based tightbinding, SF-TDDFTB, as a cost effective alternative for describing the electronic structure of S 0 and S 1 states in isomerisation reactions. As any SF method, one of the main advantages is the convergence of a single-determinant triplet reference, facilitating the convergence of the reference SCF in cases in which the ground-state wavefunction becomes multiconfigurational, such as during bond-dissociation or near conical intersections with the ground state. We have shown that the excited state energies as well as the optimized geometries for the ground state and conical intersection are qualitatively and quantitatively similar to the all electron spin-flip calculations based on SF/MRSF-TDDFT, at a fraction of computational cost. In general, SF-TDDFTB calculations take less than 1 second on a single CPU for converging the SCF and solving the response equations, whereas the all-electron calculations take between 2 to 15 minutes in 12 CPUs. In conclusion, SF-TDDFTB is a promising method for performing statistically relevant calculations of isomerisation quantum yields in conjunction with semi-classical non-adiabatic molecular dynamics.