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Fluorescence spectra and lifetimes of carbazole, 1,3-bis(N-carbazolyl)propane and poly (N-vinylcarbazole) have been studied as a function of pressure to 30 kbar at room temperature and nOK. Polymer films show exclusively excimer fluorescence (,.=43 nsec) at room temperature. This is not quenched at nOK but appears together with a new emission (,.= 12 nsec) attributed to traps arising from exciton coupling between adjacent carbazole chromophores. The comparative P, T response of the three compounds suggests that excimers do not form between adjacent chromophores in the amorphous polymer.The possibility to use a partitioning of the first-order density matrix to obtain a quantum mechanical basis for bond energy schemes is pointed out. Methods for obtaining such partitionings are discussed. The problems arising, when a bond energy scheme is based on the kinetic energy of the electrons is discussed in the light of the quantum mechanical virial theorem. A small numerical example is given.

The fluorescence spectra of crystalline chrysene, 1,2-benzanthracene, anthracene, and four derivatives of anthracene were surveyed in the 0–25-kbar pressure range. In addition to stronger reabsorption of the crystal fluorescence upon compression, a pressure exceeding 10 kbar results in significant modifications of the spectrum. Diffuse bands at longer wavelengths appear at the higher pressures and may be attributed to a reorientation of the molecules in the lattice and the creation of many defects, which favors excimer interaction. The effect is largest for anthracene, where the initial intensity distribution at 1 atm generally does not return after high pressures have been applied. The results appear to depend significantly upon the crystal size and preparation.

The pressure dependence of pyrene fluorescence in toluene has been measured to 10 kbar. The monomer and excimer fluorescence decay kinetics are analyzed to give the rate parameters for excimer formation, dissociation, and unimolecular decay as a function of pressure at 296, 320, and 340°K. Activation parameters are evaluated both as a function of temperature and as a function of pressure. The pressure dependence of the association is in one-to-one correspondence with the solvent viscosity. The rate of dissociation is strongly inhibited by high pressures. The volume change on excimer formation is −11 cm3/mole at 296°K. The enthalpy and free energy of excimer formation are −9.7 and −4.2 kcal/mole at 1 atm, and −3.6 and −6.7 kcal/mole at 10 kbar, respectively.

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