The accurate potentials of Ph2I+ cation reduction, yielding in one step Ph-center dot and PhI, are equal to -0.68, -0.61 and -0.67 V vs. SCE, in MeCN, DMF and water, respectively, according to state-of-the-art quantum chemical calculations using the benchmark gas-phase energetics (the C-I bond homolytic dissociation energy in Ph2I+ and electron affinity of PhI center dot+) from the explicitly correlated coupled-cluster method (CCSD(T)-F12) together with the SMD solvation free energies. The alkyl (Me or t-Bu) substitution effect on the reduction potential of Ph2I+ was estimated to be less than 50 mV. It was demonstrated that employing the ubiquitously used erroneous E degrees(Ph2I+) value of -0.2 V in the prediction of Delta G degrees for photoinduced electron transfer may lead to failed photoinitiated polymerisation experiments. (C) 2017 Elsevier Ltd. All rights reserved.