2. COLORSoF DYES: ELECTRONS INBoxES Cyanine dyes are organic molecules that cont
ID: 1070218 • Letter: 2
Question
2. COLORSoF DYES: ELECTRONS INBoxES Cyanine dyes are organic molecules that contain conjugated bonds. This problem deals with one such dye. Its structural formula is shown below. Dye C The conjugated system (shown above)is what you wil use to answerthe questions below. The R electrons in the conjugated system can be thought of as particles in a box, the dye molecule being the box. Since the two nitrogen atoms at each end represent a substantal disruption of the conjugated system, they can be thought of as the walls of the box. Dye C appears colored to the naked eye. The objectof this problem calculate the wavelength of maximum absorption for the dye, assuming the molecule is acting as a particle-in-a-box system. From the wavelength of maximum absorption you should be able to predict the color the dye. angins of color When light (electromagnetic radiation) hits an object, some of the photons can be absorbed f the energy of the photon matches the diference between two electon energy levels in the object's molecules. Era-hxv AE For example, in the diagram at right, a photon with energy 10.2eVcan be absorbed and as a consequence an electron can transition from the ground state to the first excited state. If the absorbed photon(s) are in the visible region, the object wil appear colored to the naked eye. Specificaly, an observer wil see the complementary color to the color that has been absorbed. For example, if yellow photons are absorbed, the object wil appear purple.Explanation / Answer
d) L = N x l
l = lenght of C=C bond = 1.5 A0
N = number of electrons = 10
L = 10 X 1.5 = 15 A0
e) The energy required to exciet outermost electron = E = hc/ wavelength
E = 6.64 X 10^-34 X 3 X 10^8 / 1.5 X 10^-10
E = 1.328 X 10^-15 Joules
f) Frequency = c / wavelength = 3 X 10^8 / 1.5 X 10^-10 = 2 X 10^18 Hz
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