Why is the boiling point of trichlorofluoromethane lower than that of chloroform?
The main reason acting here is Dipole Moment. The higher the dipole moment of a molecule, the greater will be the intermolecular attractive forces and the higher will its boiling point be.
Dipole moment is the displacement of electron density in a molecule and it is a vector quantity. The net dipole moment of a molecule is the vector summation of all the individual dipole moment of 2 bonded atoms created by the electronegativity difference between them.
So, at first, let's get the structure of the molecules. Both of them are sp3 hybridised and have a tetrahedral structure.


For CHCl3, if you consider the bond between carbon and chlorine, its highly polar. Due to the high electronegativity of chlorine, there will be a net negative pole on the bottom part caused by the three Carbon chlorine bonds. And Hydrogen being less electronegative,however, will not attract the electrons to a great extent. Hence, there will be a pretty significant net dipole moment in CHCl3.

But in the case of CFCl3, yes, there will be a charge separation by the chlorine atoms, but on the upper portion lies the F atom which is very electro-negative. As a result, it will also pull its bond pair of electrons towards itself. Since, the net dipole moment is the vector summation of the individual dipoles, the charge separation of C-F, being in the opposite direction of the charge separation by the 3 chlorine atoms, will reduce the net dipole moment of the molecule.


For this reason, the dipole moment of CHCl3 is more than that of CFCl3 and so, CHCl3 has a higher boiling point.