Question

How is the geometry of molecule change if an electron is excited from HOMO to LOMO?

The structure was Opt+freq using B3LYP/cc-PVDZ and the following MO diagram was obtained. what should i expect is the geometry changes the molecule to undergo if it an electron is excited from the HOMO to the LUMO?

I41 0.34458 40一一 0.33636 39 0.07535 口 -0.24863 3 8 -0.47122 37 0.47230 36 35 -0.47278 41 0.34458 40- 0.33636 0.07535. 39 -0.24863 口 37 -0.47122 36 ー -0.47230 -0.47278

Answer 1

There is no change in the geometry of the compound when electrons move from HOMO to LOMO( LUMO) rather there are chemical changes that take place. As the transfer of electrons energize the bonds over which the transfer has occurred.thus activating or deactivating bonds chemically.

As we can also see from the diagram that the 1st transition shown when there is a transfer from 39 to 38 has shown a different electron transfer cloud (solid green and red spheres) and when the transfer is from 38 to 39 there are more number of spheres that is more splitting that is an indication of increase in energy and a transfer to LUMO.

Thus we must not expect a geometry change when there is a transfer from HOMO to LUMO or vice versa.