Experiments involving rotational coherence spectroscopy have measured moments of inertia of the jet-cooled 1:1 complex of perylene with naphthalene in the S-1 state. This complex is found to have overlapped rings, resembling the 1:1 complex of perylene with benzene. The high rotational symmetry of the aggregate prevents unambiguous determination of the angle subtended by the molecular long axes. Two possible structures are therefore suggested, corresponding to parallel and perpendicular alignment of the molecular long axes. The effects of vibronic excitation for both the benzene and naphthalene 1:1 complexes of perylene were also investigated. Electronic-origin excitation of either complex results in prominent rotational coherence transients. The signals persisted with the same amplitude for 353 cm(-1) vibronic excitation of naphthalene and were still present, at reduced intensity, at 705 cm(-1) The naphthalene complex shows little or no vibrational coupling for these excitation energies. On the other hand, vibronic excitation of the benzene complex at greater than or equal to 353 cm(-1) or the naphthalene complex at 540 cm(-1) showed no rotational coherence signal, both cases signifying the occurrence of vibration-rotation coupling.