The fluorescence of dimesityl-pyrroloboranes with different ground state twist angles is investigated by absorption, steady state, and time-resolved fluorescence spectroscopies. Only one strongly Stokes shifted charge transfer fluorescence band is found, characterized by monoexponential decays. This fluorescence is connected with extremely low fluorescence rate constants (k(f) = (1-2) x 10(6) s(-1)) which are nearly solvent and temperature independent and indicate the forbidden character of the emission. The pretwisted compound shows reduced k(f) values and only a lengthening of the lifetimes with decreasing temperature whereas the planar compound shows a lifetime maximum (increase followed by decrease) upon cooling. This is interpreted as evidence that the planar compound relaxes to a more twisted structure in the excited state. Large-scale ab initio CI calculations on a smaller model system confirm the nearly full charge-transfer character present for all twist angles and the energy minimum in the excited state for twisted geometries.