Detailed photophysical studies of the emitting triplet state of the highly phosphorescent compound Pt(dpyb)Cl based on high-resolution optical spectroscopy at cryogenic temperatures are presented {dpyb = NC-2N-coordinated 1,3-di(pyridylbenzene)}. The results reveal a total zero-field splitting of the emitting triplet state T-1 of 10 cm(-1) and relatively short individual decay times for the two higher lying T-1 substates II and III, while the decay time of the lowest substate I is distinctly longer. Further evidence for the assignment of the T-1 substates is gained by emission measurements under high magnetic fields, Distinct differences are observed in the vibrational satellite structures of the emissions from the substates I and II, which are dominated by Herzberg-Teller and Franck-Condon activity, respectively. At T=1.2 K, the individual spectra of these two substates can be separated by time-resolved spectroscopy. For the most prominent Franck-Condon active modes, Huang-Rhys parameters of S approximate to 0.1 can be determined, which are characteristic of very small geometry rearrangements between the singlet ground state and the triplet state T-1. The similar geometries are ascribed to the high rigidity of the Pt(NCN) system which, unlike complexes incorporating bidentate phenylpyridine-type ligands and exhibiting similar metal-to-ligand charge transfer admixtures, cannot readily distort from planarity. The results provide new insight into strategies for optimizing the performance of platinum-based emitters for applications such as organic light-emitting diode (OLED) technology and imaging.