A method of screening a library comprising: (i) providing either (a) a library comprising more than one copy of different library members, each copy of a different library member attached to a different releasable tag through a releasable covalent bond; where a plurality of tags uniquely encode each library member; or (b) a library comprising one or more copies of a library member attached to a support, with a plurality of tags uniquely encoding each library member; or (c) a library comprising different library members, each different library member attached to a plurality of tags uniquely encoding the different library member; (ii) providing a target compound with tethered sensitizer in specific binding proximity to the library, allowing specific binding of the target compound with tethered sensitizer to a selected library member; (iii) exciting the tethered sensitizer with excitation photoradiation, whereby the releasable tags attached to the selected library member are released; and (iv) detecting the releasable tags.