Excited-state dynamics of 4-dimethylamino-4′-nitrobiphenyl confined in AOT reverse micelles

We report the excited-state intramolecular charge transfer (ICT) dynamics of 4-dimethylamino-4′-nitrobiphenyl (DNBP) in the reverse micelles (RMs) of bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) by time-resolved fluorescence and transient absorption spectroscopy. The absorption and emission bands of DNBP in the RMs appeared as blue-shifted from the maximum wavelengths of bulk methanol solution, which can be understood as the decrease of solvent polarity in the RMs. The quantum yield and excited-state lifetime of DNBP in the RMs increase enormously upon the decrease of the micelle size, which is interpreted as the decrease of the micropolarity and the increase of microviscosity in the small RMs. The efficient intersystem crossing to the triplet states and strong phosphorescence of DNBP in the near-infrared region was also observed in the small RMs, which results from the strongly restricted torsional relaxation of biphenyl group in the confined environments of the small RMs. We have observed the site-specific and micelle size-dependent excited-state dynamics of DNBP in the methanol/AOT/isooctane RMs, which may originate from the less homogeneous environment of the confined solvent pools of the RMs than bulk. [Display omitted] •Intramolecular charge transfer of DNBP coupled with torsional dynamics of biphenyl•Micropolarity of methanol decreases inside methanol/AOT/isooctane reverse micelles.•Microviscosity of methanol increases strongly in small AOT reverse micelles.•Quantum yield and lifetime of DNBP are strongly increased in small reverse micelles.•Triplet state of DNBP in small reverse micelles due to restricted torsional motion