One- and two-photon excitation spectra, as well as absorption and emission spectra of diphenyloctatetraene (DPOT) in n-alkanes are investigated at low temperatures. For DPOT in n-octane we report on the measurements of one-photon excitation and emission spectra and for DPOT in n-tetradecane (TD) on the measurements of one- and two-photon excitation spectra and emission spectra. The spectra are governed by the transitions between the electronic ground (S-0) and the two lowest electronic excited singlet states (S-1,S-2). The interpretation is based on allowed transitions and transitions induced by the S-1-S-2 coupling due to Herzberg-Teller promoting modes or due to static lattice-induced distortions of DPOT. A single noncentrosymmetric site is observed for DPOT in n-octane. For DPOT in TD a centrosymmetric and a noncentrosymmetric site are reported. The analysis indicates that there is a dynamical equilibrium in the population of these two sites. The experimental data are quantitatively studied by comparison with simulated spectra. The simulation calculations are based on the coupling between nonadiabatic S-1 and S-2 states, harmonic modes, and suitable transition moments and line-shape functions. For DPOT in TD the calculations reveal an interesting interference pattern in the vibronic progressions observed in two-photon excitation spectra.