What is the frequency and wavelength of a photon absorbed in the transition of an electron from the n=5 to the n=8 of dye #3 (1-1’-diethyl-2-2’-dicarbocyanine iodide).

to do this calculation, you will need to make a reasonable assumption for the value of l. as a first approximation, we will assume that the value of lcc in these molecules is the same as in benzene and pyridine, two similar delocalized systems: lcc = 0.140 nm (benzene) lcn = 0.134 nm (pyridine)

the aromatic rings capping the ends of the dye molecules complicate the unambiguous assignment of length. indeed, several reasonable choices are possible. one simple choice is assume the length of the molecule to be from one n atom to the other n atom. the effect of the rest of the aromatic rings is then considered to be absorbed into the parameter ‘p’ (equation 7). considering the information given above, estimate the value of ‘p’. ex: do you think the electron will penetrate far outside the nitrogen caps, or vice versa? (after comparing your predictions to the experiment, you will be able to derive a more accurate value for ‘p’.)