The general Weller scheme I (according to classification of schemes proposed in Ref. [1] and commonly used afterwards) describes the contact exciplex formation accounting for its subsequent transformation into radical ion pair (RIP), subjected to separation into free ions and geminate recombination after spin conversion. The reversible triplet formation (due to RIP recombination) and its natural decay, enhanced by the impurity quenching in the bulk, are also taken into account. The Stern-Volmer constant of fluorescence quenching by reversible exciplex formation is specified as well as its free energy dependence similar to the Rehm-Weller one. (C) 2011 Elsevier B.V. All rights reserved.