From what I read Visser and van Hoek (1981) assumed that NADH and NADPH shows a multi-exponential fluorescence decay due to intramolecular interaction such as folding (therefore interaction with adenin part of NAD(P)H).

In contrast to that, there are papers (e.g. G. Krishnamoorthy: On the Origin of heterogeneity of fluorescence decay kinetics of NAD(P)H, 1987) that show that the multi.exp. decay originates solely from "intrinsic photoprocesses" of the dihydronicotinamid moiety.

My question: What "intrinsic photoprocesses" are ment by the latter?

How can one dihydronicotinamid-chromophore exhibit double exponential decay?