He I photoelectron spectra. of phenanthrene (1), 1,10-phenanthroline (2), phenazine (3), dibenzo[a,c]anthracene (4), dibenzo[a,c]phenazine,(5), and dipyrido[3,2-a;2'3'-c]phenazine (6) have been obtained. Assignment of the pi ionization states was aided by electronic structure calculations: the first ionization state of 1, B-2(1)(pi(1)), is',observed at 7.888 +/-0.002 eV, B-2(2)(pi(1)) of 2 is at 8.342 +/- 0.002 eV, and B-2(1g)(pi(1)) of 3 is at 8.314 +/- 0.002 eV. Spectra of 4-6 arereported for the, first time: (2)A(2)(pi(1)) of 4 is at 7.376 +/- 0.002 eV, and both 5 (7.983 +/- 0.002 eV): and 6 (8.289 +/- 0.002 eV) exhibit quasi-degenerate first and second ionization states. Quantum-mechanical reorganization. energies, lambda(QM), were extracted from analyses of vibrational structure: values are 149 +/- 5 (1), 167 +/- 5 (2), 68 +/- 2 (3), and 92 +/- 4 (4) meV. Low-frequency modes were treated semiclassically: values of lambda(SC) are estimated to be 21 +/- 1 (1), 13 +/- 1 (2), 22 +/- 1 (3), 66 +/- 1 (4), 27 +/- 9 (5), and 16 +/- 1 (6) meV. Reorganization energies (lambda = lambda(QM) + lambda(SC)) of isolated molecules are 170 +/- 5 (1), 180 +/- 5 (2), 90 +/- 2 (3), and 158 +/- 4 (4) meV. Density functional calculations (B3LYP/6-311G++(d,p)) give lambda values that are on average 63 meV lower than experimentally derived energies.