Photoinduced coupling of an acetylene with a quinone in two wavelength regions (lambda(DB) and lambda(CT)) can be regioselective to yield a single quinone methide adduct when various diarylacetylenes (DA) and 2,6-dichlorobenzoquinone (DB) are used. Thus, the direct photoexcitation of DB at lambda(DB) = 355 nm or the specific activation of the 1:1 electron donor-acceptor complex [DA,DB] at lambda(CT) = 532 nm both lead to the transient ion-radical pair [DA(.+),DB.-], which is established by time-resolved (ps,ns) spectroscopy. Competition between back electron transfer (k(BET)) and ion-radical pair collapse (k(C)) to the distonic adduct DA-DB, as described in Schemes 1 and 2, limits the quantum yields for both photochemical processes in Table 4. The biradical nature of the distonic adduct in Scheme 3 accommodates the various facets of acetylene reactivity and unique regioselectivity to yield the same quinone methide by both actinic processes. In a more general context, the electron-transfer mechanism established by the charge-transfer excitation of [DA,DB] provides compelling evidence that the Paterno-Buchi coupling (by direct excitation of DB) can proceed via the same sequence of reactive intermediates.