This was hypothesised to be a result of the interaction between the singlet excited state of 4CzIPN and solvent molecules, which suppressed kISC as has been seen in carbene and fluorenone systems. 22,23 Indeed, Wang et al. suggested that in the carbene system, the solvated carbene must first be desolvated before ISC can occur, thus causing the kISC to decrease. This trend in kISC was proposed to be the reason behind the decrease in the photoluminescence quantum yield (FPL) in more polar solvents (94% and 18% for toluene and MeCN, respectively). By contrast, the value of kRISC was found to increase with solvent polarity (from 2.7 × 10 6 s -1 in toluene to 1.4 × 10 7 s -1 in MeCN). These findings are similarly reflected in the trends observed for pDTCz-DPmS (Table ). were determined by the onset of the room temperature photoluminescence and 77 K phosphorescence spectra, respectively. b Rates are determined using the method and assumptions outlined in reference 24 .