The absorption spectra of each component of the reaction in THF were measured (Figure ). No significant absorption could be observed for DIPEA and NHPI at the irradiation wavelength of 390 nm while PhCCBr shows a very weak absorption tail at 390 nm. By contrast, HE displays an intense absorption band that completely overlaps with the main absorption band of pDTCz-DPmS. It is worth noting that under the reaction conditions, the percentage of 390 nm light absorbed by HE is estimated to be 15-times higher in comparison to that of pDTCz-DPmS, based on their concentrations and molar extinction coefficients (e) at this wavelength.