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The conical intersection (CI) governs the ultra-fast relaxation of excited states in a radiationless manner and are observed mainly in photochemical processes. In the current work, we investigated the effects of substituents on the reaction dynamics for the conversion of gauche-1,3-butadiene to bicyclobutane via photochemical electrocyclization. We incorporated both electron withdrawing (À F) and donating (À CH 3 ) groups in the conjugated system. In our study, we optimized the minimum energy conical intersection (MECI) geometries using the multi-configurational state-averaged CASSCF approach, whereas, to study the ground state reaction pathways for the substituted derivatives, dispersion corrected, B3LYP-D3 functional was used. The non-adiabatic surface hopping molecular dynamics simulations were performed to observe the behaviour of electronic states involved throughout the photoconversion process. The results obtained from the multireference second-order perturbation correction of energy at the XMS-CASPT2 level of theory, topography analysis, and nonadiabatic dynamics suggest that the À CH 3 substituted derivatives can undergo faster thermal conversion to the product in the ground state with a smaller activation energy barrier compared to À F substituted derivative. Our study also reveals that the GBUT to BIBUT conversion follows both conrotatory and disrotatory pathways, whereas, on substitution with À F or À CH 3 , the conversion proceeds via the conrotatory pathway.

We propose a minimal model of a Coulomb-coupled fermionic quantum dot thermal diode that can act as an efficient thermal switch and exhibit complete rectification behavior, even in the presence of a small temperature gradient. Using two well-defined dimensionless system parameters, universal characteristics of the optimal heat current conditions are identified. It is shown to be independent of any system parameter and is obtained only at the mean transitions point “−0.5”, associated with the equilibrium distribution of the two fermionic reservoirs, tacitly referred to as “universal magic mean”.

We propose a minimal model of a Coulomb coupled fermionic quantum dot thermal diode that can act as an efficient thermal switch and exhibit complete rectification behaviour, even in presence of a small temperature gradient. Using two well defined dimensionless system parameters, universal characteristics of the optimal heat current condition are identified. It is shown to be independent of any system parameter and is obtained only at the mean transitions point "−0.5", associated with the equilibrium distribution of the two fermionic reservoirs, tacitly referred as "universal magic mean".