Marcus inverted region: nature of donor–acceptor pairs and free ion yields

Abstract

The free ion yield (OR) resulting from the fluorescence quenching of 9,lO-dicyanoanthracene (DCA) by various electron donors in acetonitrile has been studied using ns laser photoconductivity. The influence of the chemical nature of the doors is established in a general manner. For a given oxidation potential €,,(DID+), the rate constant of geminate ion recombination, kbac , decreases significantly as the electronic delocalization of the donor increases. As a consequence multiple Marcus plots are observed in the inverted region. These plots show decreasing curvature when going from stilbenes to amines as donors. This 'fan effect' is tentatively explained by considering the detailed roles of the parameters V , I and h v in the Marcus model.

Investigation of geminate recombination of radical ion pairs generated by dissociation of exciplexes in moderately polar solvents using the photoconductivity technique

“…The values of k et = r/Dv = 10 8 -10 9 1/s presented in Table 2 are rather close to recombination rates obtained by many investigators [17,18,[59][60][61][62][63][64][65] for those solvent-separated radical ion pairs for which the return ET energy is also about À3 eV. Fig.…”

“…At t > t max , the J 2 current slowly decreases with increasing time, so that the value of J 2 /J 0 q approaches unity from above at sufficiently long times. An insignificant decrease of photocurrent at t > t max is difficult to identify experimentally because it is superimposed on the usually observed decay of photocurrent on the microsecond scale [17][18][19] which is caused by the bulk ion recombination with ions of other photogenerated ion pairs and with ''intrinsic" ions responsible for conductivity of the sample in the dark. So, as well as in [24], we consider only a rise of the J 2 current at t < t max and define the exponential rise time t 632 by the condition…”

“…The photoconductivity technique is of frequent use for determination of quantum yields of free ion formation in the photoinduced electron transfer (ET) reactions [9,[13][14][15][16][17][18][19][20][21][22] and for measurements of excited-state dipole moments and exciplex dipole moments [23]. Recently, it has been shown [24] that measurements of transient photocurrents enable one to find the recombination rates of solvent-separated radical ion pairs in the case that the ions arise from dissociation of exciplexes, a primary product of the photoinduced ET reactions.…”

Investigations of bimolecular photoinduced electron transfer reactions in polar solvents using ultrafast spectroscopy

“…Although CR dynamics of photogenerated ion pairs has been investigated rather intensively, the CR rate constant, k CR , has been in most cases determined indirectly from the free ion yield [13,25,26,[55][56][57][58][59], Φ ion :…”

Coherent Electronic and Nuclear Dynamics for Charge Transfer in 1-Ethyl-4-(carbomethoxy)pyridinium Iodide

“…The creation of stable radicals should be most facile in complexes that are loosely bound and able to separate following excitation. [70][71][72] This process is depicted in Figure 9 as evolution from the solvent-separated to the solvated radical solute-solvent configuration. The creation of solvated radicals is a reasonable interpretation, given the high stability of 1-ethyl-4-(carbomethoxy)-pyridine in solution.…”