PHOTOLYSIS OF COVALENT COMPOUNDS COMPOSED OF STABLE ANIONS AND CATIONS - TRANSIENT ABSORPTION STUDIES ON COORDINATION-COMPLEXES FORMED FROM THE TRIPHENYLCYCLOPROPENYL CATION AND MALONITRILO, ACETONITRILO, AND FLUORENYL ANIONS

A series of molecules (1,2,3-triphenylcyclopropene (1), [3-(1,2,3-triphenylcyclopropenyl)](4'-cyanophenyl)malonitrile (2), [3-(1,2,3-triphenylcyclopropenyl)](4'-nitrophenyl)malonitrile (3), [3-(1,2,3-triphenylcyclopropenyl)](3'-nitrophenyl)malonitrile (4), [3-(1,2,3-triphenylcyclopropenyl)](4'-nitrophenyl)acetonitrile (5), and [3-(1,2,3-triphenylcyclopropenyl)]-9'-cyanofluorene (6), each composed of a stable carbanion and carbocation covalently attached to each other, has been photolysed with use of picosecond and nanosecond laser techniques. These molecules undergo a sequence of events that begins with absorption of a photon by one of two localized chromophores in each precursor (i.e., the stilbene of TPCP or the aryl portion of the starting carbanion). The singlet excited states initiate an electron transfer event at rates that were too fast to measure under the conditions employed. (The radical ions were observed within the shortest available time scale, ca. 25 ps.) The radical ion pairs have two possible alternatives: (1) back electron transfer to form the triplet excited state of the triphenylcyclopropenyl part and (2) bond fragmentation of the central bond (i.e., the one connecting the carbanion to the carbocation). Apparently, the presence of ions from the latter fragmentation depends on the relative rates of the two processes.