The coordination compounds TlTp(3-R) with Tp(3-R) = hydridotris-(3-R-pyrazolyl-1-yl)-borate anion (R = tert-butyl, phenyl, 2-thienyl and p-tolyl) show a photoluminescence which originates from the metal-centered sp triplet of the Tl+ ion. In the solid state, the emission wavelength depends on the substituent R. Since the Tl+...Tl+ distance varies with R the emission energy seems to reflect the extent of metal-metal interaction in the excited state.