Photophysics of 7-azaindole homodimer has been studied in Ar and N-2 matrixes for the first time. The infrared spectra reveal that a doubly hydrogen bonded dimer is predominantly produced upon annealing the seeded matrixes at 28 K. However, unlike in hydrocarbon solutions or a supersonic jet expansion, the matrix-isolated doubly hydrogen bonded dimer emits exclusively in ultraviolet from the locally excited state, and the vital photophysical process, the excited state double proton transfer, is slowed down dramatically. We have interpreted the observation in terms of matrix effect on the double proton transfer potential and promoting vibrational modes. (C) 2012 Elsevier B.V. All rights reserved.