Qualitatively essential is the distribution and size of the Pi-electron system of conjugated double bonds as its size but also the distribution of the electron density determines the energy for the transition to the first excited state. Chl f has a formyl group instead of methyl group as compared to Chl a - so it sounds reasonable that it´s (Chl f) larger Pi-electron system shifts absorption to the red. Imagine a larger quantum well where the energetic distance of the states reduces with size of the quantum well. So very small quantum wells / Pi- electron systems shift to the blue with absorption maximum of the Qy band. However this argumentation is not straight forward if you look at different structures. especially from Chl b one would rather expect a red shift as compared to Chl a instead of the blue shift as there is also a methyl group replaced by formyl. So one can draw the opposite conclusion when arguing with the simple quantum well. To understand the spectra quantitatively one would need to do a quantum chemical calculations (e.g. density functional theory) which can be done and describe the spectra quite successfully:

Article Spectroscopic Properties of Chlorophyll f

Very nice and creative question indeed. Ok so far I know the basic difference between Chlorophyll a, d, f and c are in the structure Carbon and Hydrogen.

Basically difference lies in chemical structure, formula and addition of substitution on main head of chlorophyll structure