Fluorescence on−off blinking of single perylenediimide (DMP−PDI) dyes embedded in a disordered matrix of poly(methyl methacrylate) (PMMA) was investigated by single-molecule fluorescence spectroscopy. In particular, we examined the bin-time dependencies of the complementary cumulative distribution functions (cCDF) of the on-time and off-time durations. It appears that intersystem crossing (ISC) within DMP−PDI competes with charge transfer between DMP−PDI and PMMA. The single-molecule and ensemble cCDFs of the on-time and off-time durations (induced by charge transfer) were best described by Weibull functions and log-normal functions, respectively. The dispersive kinetics of the on-time duration were attributed to radical ion pair ISC from triplet charge separation ( 3 CS) state to the corresponding singlet ( 1 CS) state via charge hopping between charge trap sites in PMMA. This process should compete with triplet charge recombination ( 3 CR), which restores the triplet state. On-to-off switching occurs only when 3 CS → 1 CS ISC overcomes the 3 CR process. The resultant Weibull distribution (with A < 1) reflects that the probability of charge hopping rapidly decreases with time. On the other hand, the offtime log-normal kinetics of single-molecules are explained by a Gaussian distribution of activation energies for charge recombination (the so-called Albery model). A simulation study revealed that the ensemble off-time cCDF included power-law kinetics of charge hopping in the polymer matrix.

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Objective To investigate the utility of the voxel-based specific regional analysis system for Alzheimer’s disease (VSRAD). Methods Clinical data from patients who underwent screening for dementia using VSRAD and the Japanese version of COGNISTAT, the Neurobehavioral Cognitive Status Examination, were retrospectively investigated to specify the domains of cognitive function that correlate with the statistical mean value of positive Z-scores in the target volume-of-interest (VOI). A receiver operating characteristic (ROC) curve was constructed to assess the mean value of positive Z-scores in discriminating patients with AD. Results A total of 72 patients were included (18 male and 54 female; 15 patients with AD). The mean value of positive Z-scores in the target VOI was significantly correlated with standardized COGNISTAT scores for Orientation and Memory in all patients (r = –0.35 and –0.38, respectively). ROC curve analysis revealed that a cut-off of 1.57 for mean value of positive Z-scores in the target VOI provided 69.4% accuracy in discriminating patients with AD, with a sensitivity of 0.80 and specificity of 0.67. Conclusions The results evinced the value of VSRAD in diagnosing AD. The degree of atrophy represented by the target VOI may reflect impairments in Orientation and Memory, which are early stage symptoms observed in AD.