C1 has an absorption maximum at 283 nm, which is not ideal for CL triggering. To gain insight in the photodegradation process of crosslinker C1, we performed an irradiation experiment in which one sample was irradiated with UV-C light (254 nm, 1.02 mW/cm 2 ) and one sample was kept in the dark as a control. We found that the absorption (283 nm) of the light irradiated sample decreases and shifts with increasing irradiation time, indicating photocleavage of C1 (Figure and 2B (green data)), while the non-irradiated sample remained stable over time (black data, Figure ). Using standard Cu-click conditions (CuSO4 (0.47 mM), sodium ascorbate (3.0 mM), activating ligand: Tris(3hydroxypropyltriazolylmethyl)amine (THTPA) (0.24 mM)), crosslinker C1 and alkyne modified dextran (500 kDa, DS = 36%, Figure ) were reacted to prepare transparent self-supporting dextran hydrogels (Figure ), having a storage modulus (G') of 4.3 * 10 2 Pa and tan d (G''/G') of 6.7 * 10 -3 (Figure ). These hydrogels were loaded with doxorubicin (Figure ) and the washed hydrogels were then placed in fresh H2O (25 ml) and irradiated with UV-C light (254 nm, 1.02 mW/cm 2 ) (Figure ). Aliquots were collected at selected timepoints over a period of 24 hours (Figure ) and UV/Vis analysis showed a linear increase of absorbance at 480 nm, which is doxorubicin's absorption maximum. Unfortunately, the observed increase in absorbance was very small, which is likely caused by the simultaneous photo degradation of doxorubicin. In the same experiment, a 5-fold increase in absorbance at 283 nm was observed which is contributed to degradation products of doxorubicin (Figure ). Although the photodegradation of doxorubicin is undesirable, the experiment does demonstrate that C1 phenacyl works as a photolabile crosslinker as the hydrogels completely disintegrated upon UV-C irradiation (Figure ), in contrast with the control hydrogels that remained intact and retained the loaded doxorubicin within the hydrogel matrix (Figure ). In this stage of the research we opted to develop a p-extended analogue of crosslinker C1, which would absorb light in the UV-A region to trigger its photocleavage. This would enable the release of proteins using our hydrogels. Since many proteins often do not absorb light above 300 nm, we expected no interference during light irradiation experiments. Also, the emission maximum of CL is centred around 380 nm light, and the increased overlap of the CL window with the absorbance spectrum of the new crosslinker would increase the efficiency of our system. We synthesized crosslinker C2 which has an extended conjugated p-system compared to crosslinker C1 and has a maximum absorbance at 383 nm, instead of 283 nm. The synthesis of bis-azide crosslinker C2 was started with the mesylation of 3-azido-propanol and the subsequent coupling with 4-ethynyl-aniline afforded alkyne 10 (Scheme 2).