The salient features in the absorption and emission spectra of alphaT4 aggregates (see Figure) and films are fully accounted for using a model based on linear exciton-phonon coupling and structural defects. In particular, the Davydov splitting is calculated to be of the order of 1 eV, and the unusually small 0-0 emission intensity is attributed to the high sensitivity of the 0-0 intensity to basal plane structural defects.