Evaluation of configuration coordinate parameters from high pressure optical data. I. Phenanthrene, anthracene, and tetracene

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Abstract
A configuration coordinate model has been developed which relates the shift of optical absorption and emission peaks with pressure and the changes of half‐width with pressure to the change in volume of the system upon electronic excitation, Δ, the ratio R of force constants of the excited and ground states, and the coupling of the force constant to the bulk modulus of the surroundings. The configuration coordinate which couples most strongly to the pressure is an inter molecular one. The analysis is applied to phenanthrene and anthracene in the crystalline state, in PMMA, and in hexane. Some data are also presented for crystalline tetracene, for anthracene in methanol and glycerol, and for benzene in hexane and water. Evaluation of these parameters by various combinations of absorption and emission data give consistent results within the precision of the data. The volume contraction upon excitation is significantly larger for anthracene than for phenanthrene, consistent with the larger dipole moment and stronger interaction of the 1La state with the surroundings compared with the 1Lb state. The volume contraction varies with the medium depending on the polarizability and compressibility of the medium. The coupling to the surrounding depends strongly on the rigidity of the medium. A brief discussion of the solvent effects in terms of dielectric theory is also given.