Relativistic two-component density functional study of ethyl 2-(2-Iodobenzylidenehydrazinyl)thiazole-4-carboxylate

[Display omitted] •Relativistic two-component method sf-X2C-TD-DFT that takes in account scalar relativistic effects infinite order via the spin-free part of the X2C Hamiltonian (sf-X2C) but spin–orbit couplings to first order via the Douglas–Kroll–Hess type of spin–orbit operator resulting also from the spin separation of the X2C Hamiltonian has been employed to explore the electronic spectrum of 2-(2-Iodobenzylidenehydrazinyl)thiazole (2d).•Its possible role to be used as an efficient photosensitizer has been explored by evaluating spin–orbit couplings between its important states of different multiplicities.•Reasons for high spin–orbit couplings have been fully uncovered. Relativistic two-component density functional theory employing sf-X2C-S-TD-DFT/SOC method has been used to explore the detailed electronic spectra of molecules with thiazole skeleton named as ethyl 2-(2-Iodobenzylidenehydrazinyl)thiazole-4-carboxylate (2d) and its meta and para isomers (2e and 2f). Four different kinds of functionals including hybrid, meta-hybrid and long-range types have been employed to explore coupled states in 2d, 2e and 2f. Electronic excited states computed with different functionals has been benchmarked with second-order algebraic diagrammatic construction method i.e. ADC(2). However, spin–orbit couplings between electronic states of different multiplicities are only computed with sf-X2C-S-TD-DFT/SOC method. It has been explored that; excited electronic states which involved transitions into sigma antibonding orbital (σ∗) between carbon and iodine atom gives birth to strong spin–orbit couplings. Thus, transitions that involve the addition or removal of electron density along the carbon-iodine bond lead to strongly coupled states.