Knowledge Bank

The wavelengths of an electronic absorption band of a chromophore, C in a medium M, is given to the second order of perturbation by \begin{equation}\lambda=\lambda_{o}(1+\frac{\phi}{{R}^{6}}\quad \frac{\alpha_{M}}{{I}{M}}|{r}{C}|^{2})+\mbox{ terms relating to other transitions}\end{equation} where $\alpha M,IM,rC,\varphi$,and R are respectively polarizability, ionization energy, transition moment, coordination number and internuclear distance. The solvents used were ROH $(\alpha /I\sim .298)RNH2$ (.525) and RSH (.930), which have in common an unshared pair of electrons on a single atom and no multiple bonds. The effect of these solvents on the first and second transitions of naphthalene, anthracene and naphthacene have been determined. The results obtained are in good qualitative agreement with respect to variation in $\alpha /1$. The dependency on $|rC|2$ is similar to that obtained in the pressure experiments described in the following paper. The addition of mercaptan to naphthacene completely changes the naphthacene spectrum. Because of the high electron affinity of the naphthacene and the low ionization energy of the mercaptan, this result may be attributable to a charge-transfer interaction. If the change in solubility of the chromophore can be attributed to the change in dispersion forces one may write {RT}{In}{S}/{S}{o}=\frac{(\lambda-\lambda{o}){I}{B}}{\lambda{o}} This relation was found to be qualitatively obeyed.