A process for crosslinking a blocked isocyanate (b) and an H-donor (c), by admixing said components with a photolatent base catalyst (a) of the formula wherein R 1 is an aromatic or heteroaromatic radical which is capable of absorbing light in the wavelength range from 200 to 650 nm and which is unsubstituted or substituted by one ore more C 1 -C 18 -alkyl, C 2 -C 18 -alkenyl, C 2 -C 18 -alkyinyl, C 1 -C 18 -haloalkyl, NR 8 R 9, CN, OR 10, SR 10, COR 11, COOR 12, halogen or or R 1 is R 2 and R 3 independently of each other are hydrogen, C 1 -C 18 -alkyl, C 1 -C 18 -alkenyl, C 3 -C 18 -alkinyl or phenyl which is unsubstituted or substituted by one or more C 1 -C 18 -alkyl, CN, OR 12, SR 12, halogen, or C 1 -C 18 -haloalkyl; R 5 is C 1 -C 18 -alkyl or NR 10 R 11; R 4, R 6, R 7, R 8 and R 9 independently of one another are hydrogen or C 1 -C 18 -alkyl; or R 4 and R 6 together form a C 2 -C 12 -alkylene bridge which is unsubstituted or substituted by one ore more C 1 -C 4 -alkyl; or R 5 and R 7, independently of R 4 and R 6, together form a C 2 -C 12 alkylene bridge which is unsubstituted or substituted by one ore more C 1 -C 4 -alkyl or, if R 5 is NR 10 R 11, R 7 and R 11 together form a C 2 -C 12 -alkylene bridge which is unsubstituted or substituted by one ore more C 1 -C 4 -alkyl; R 10, R 11 and R 12 independently of each other are hydrogen or C 1 -C 18 alkyl; R 13 is an aromatic or heteroaromatic radical which is capable of absorbing light in the wavelength range from 200 to 650 nm and which is unsubstituted or substituted by one ore more of the substituents C 1 -C 18 alkyl, C 2 -C 18 -alkenyl, C 2 -C 18 -alkinyl, C 1 -C 18 -haloalkyl, NR 8 R 9, CN, OR 10, SR 10, COR 11, COOR 12, or halogen; R 14 is hydrogen or C 1 -C 18 -alkyl; R 15 is hydrogen, C 1 -C 18 -alkyl or phenyl which is unsubstituted or substituted by one or more C 1 -C 18 -alkyl, vinyl, C 3 -C 18 -alkenyl, C 3 -C 18 -alkinyl, C 1 -C 18 -haloalkyl, phenyl, NR 8 R 9, CN, OR 10, SR 10, COR 11, COOR 12 or halogen; and irradiating the composition with light of a wavelength range of 200-650 nm. R 1 is an aromatic or heteroaromatic radical which is capable of absorbing light in the wavelength range from 200 to 650 nm and which is unsubstituted or substituted by one ore more C 1 -C 18 -alkyl, C 2 -C 18 -alkenyl, C 2 -C 18 -alkyinyl, C 1 -C 18 -haloalkyl, NR 8 R 9, CN, OR 10, SR 10, COR 11, COOR 12, halogen or or R 1 is R 2 and R 3 independently of each other are hydrogen, C 1 -C 18 -alkyl, C 1 -C 18 -alkenyl, C 3 -C 18 -alkinyl or phenyl which is unsubstituted or substituted by one or more C 1 -C 18 -alkyl, CN, OR 12, SR 12, halogen, or C 1 -C 18 -haloalkyl; R 5 is C 1 -C 18 -alkyl or NR 10 R 11; R 4, R 6, R 7, R 8 and R 9 independently of one another are hydrogen or C 1 -C 18 -alkyl; or R 4 and R 6 together form a C 2 -C 12 -alkylene bridge which is unsubstituted or substituted by one ore more C 1 -C 4 -alkyl; or R 5 and R 7, independently of R 4 and R 6, together form a C 2 -C 12 alkylene bridge which is unsubstituted or substituted by one ore more C 1 -C 4 -alkyl or, if R 5 is NR 10 R 11, R 7 and R 11 together form a C 2 -C 12 -alkylene bridge which is unsubstituted or substituted by one ore more C 1 -C 4 -alkyl; R 10, R 11 and R 12 independently of each other are hydrogen or C 1 -C 18 alkyl; R 13 is an aromatic or heteroaromatic radical which is capable of absorbing light in the wavelength range from 200 to 650 nm and which is unsubstituted or substituted by one ore more of the substituents C 1 -C 18 alkyl, C 2 -C 18 -alkenyl, C 2 -C 18 -alkinyl, C 1 -C 18 -haloalkyl, NR 8 R 9, CN, OR 10, SR 10, COR 11, COOR 12, or halogen; R 14 is hydrogen or C 1 -C 18 -alkyl; R 15 is hydrogen, C 1 -C 18 -alkyl or phenyl which is unsubstituted or substituted by one or more C 1 -C 18 -alkyl, vinyl, C 3 -C 18 -alkenyl, C 3 -C 18 -alkinyl, C 1 -C 18 -haloalkyl, phenyl, NR 8 R 9, CN, OR 10, SR 10, COR 11, COOR 12 or halogen;