Exciton transport and relaxation in optically excited phenylacetylene dendrimers is simulated using the Redfield equations. The interplay of entropic (periphery-bound) and energetic (center-bound) driving forces is explored. The fluorescence signal computed using the Doorway-Window representation provides a direct probe for exciton dynamics. The propagated exciton density matrix is analyzed and several measures of the time-dependent excitonic coherence sizes are proposed and calculated. (C) 2001 American Institute of Physics.