Discrimination and interpretation of spectral phenomena by room-temperature single-molecule spectroscopy

The single-molecule fluorescence properties of the two perylenediimide dyes , 9-amino-N-(2,6-diisopropylphenyl)perylene-3,4-dicarboximide (API), and th e derivative NN-di(tert-butoxycarbonyl)-API (DAPI), are investigated in the amorphous host polystyrene at room temperature. For API, three spectroscop ically different types of spectra can be distinguished, two of them can be assigned to the off-resonance and the in-resonance conformer of the amino g roup and the chromophore's pi -electron system, repectively. The bathochrom ic third spectrum is suggested to originate also from an off-resonance conf ormer. In accordance with the sterically demanding substituents only off-re sonance spectra are found for DAPI. Not being limited by the inhomogeneous spectral distribution, many molecules show clearly resolved vibronic struct ure and can be characterized by their spectral means, the vibronic maxima p ositions, and the vibronic band gaps. Sequences of consecutive spectra reve al different forms of dynamic behavior such as diffusion and abrupt jumps, both in the spectral domain and in the intensity trajectories. These can be summarized in a rough classification of the observed dynamic phenomena.