▁( tri ple t ▁exc it ons ) ▁may ▁be ▁used ▁for ▁emission ▁when ▁do ping ▁an ▁organ ic ▁sem icon duct or ▁matrix ▁with ▁a ▁ph osph ores cent ▁d ye , ▁such ▁as ▁complex es ▁of ▁ir id ium ▁with ▁strong ▁spin – or bit ▁coupling . ▁ ▁Work ▁on ▁conduct ivity ▁of ▁anth rac ene ▁cry st als ▁contact ed ▁with ▁an ▁electro ly te ▁showed ▁that ▁opt ically ▁excited ▁d ye ▁mole cules ▁ad s or bed ▁at ▁the ▁surface ▁of ▁the ▁cry stal ▁inject ▁charge ▁carri ers . ▁The ▁underlying ▁phenomen on ▁is ▁called ▁sens it ized ▁photo con duct ivity . ▁It ▁occurs ▁when ▁photo - ex c iting ▁a ▁d ye ▁mole c ule ▁with ▁appropriate ▁ox id ation / redu ction ▁potential ▁ad s or bed ▁at ▁the ▁surface ▁or ▁incorpor ated ▁in ▁the ▁bulk . ▁This ▁effect ▁revolution ized ▁elect roph ot ography , ▁which ▁is ▁the ▁techn ological ▁basis ▁of ▁today ' s ▁office ▁copying ▁machines . ▁It ▁is ▁also ▁the ▁basis ▁of ▁organ ic ▁solar ▁cells ▁( OS C s ), ▁in ▁which ▁the ▁active ▁element ▁is ▁an ▁electron ▁don or , ▁and ▁an ▁electron ▁accept or ▁material ▁is ▁combined ▁in ▁a ▁bil ayer ▁or ▁a ▁bulk ▁heter oj unction . ▁ ▁D op ing ▁with ▁strong ▁electron ▁don or ▁or ▁accept ors ▁can ▁render ▁organ ic ▁sol ids ▁conduct ive ▁even ▁in ▁the ▁absence ▁of ▁light . ▁Ex amples ▁are ▁do ped ▁poly ac et yl ene ▁and ▁do ped ▁light