Steady-stateUV–visible absorption and emission togetherwith femto to nanosecond time-resolved emission techniques have beenapplied to study the dynamics of 3-(2-N-methylbenzimidazolyl)-7-(N,N-diethylamino)coumarin (C30) in neatsolvents, as well as in the presence of chemical (β-CD and DM-β-CD)and biological (HSA protein) cavities. The formation of inclusioncomplexes inside the hydrophobic CDs gives 1:1 and 1:2 guest:hostcomplexes, whereas with the HSA protein, the formed 1:1 inclusioncomplexes are more robust. The picosecond experiments show the importanceof the interactions of C30 with the medium, as well as the intramolecularevents in the excited-state relaxation as evidenced by the increasein the global emission lifetime from ∼0.5 ns in MeOH/H2O mixtures to 2.5 ns in THF, and to 1–3 ns when thedye is trapped within CDs and HSA cavities. Time-resolved anisotropy(r(t)) results indicate the involvementof ultrafast depolarization processes, whereas in the MeOH/H2O mixtures r(0) = 0.27, in DM-β-CD, r(0) = 0.35. The rotational time decays clearly show therobustness of the formed complexes with CDs and HSA protein: ∼170ps in MeOH/H2O solvent mixtures, ∼850 ps due to1:1 and 1:2 β-CD complexes, and 28 ns for HSA complexes. Thefemtosecond time-resolved emission experiments reveal the significantchanges of the dynamics with the encapsulation of C30 by CDs (fromapproximately τ1= 0.3 and τ2=2 ps in THF to approximately τ1= 1.0 and τ2= 7.5 ps in the MeOH/H2O binary mixture, and to approximatelyτ1= 3 and τ2= 30 ps in the CDcomplexes). The change is explained in terms of how the water moleculesmodulate the intramolecular charge transfer (ICT) time (τ1) and how the restriction of the environment modifies thetorsional process (τ2). In the case of trapped C30within the HSA protein the intermolecular interactions with the aminoacid residues are revealed, giving rise to a complex photodynamicalbehavior due to the hydrophobic, H-bonding, electrostatic, and polarnature of the heterogeneous environment inside the protein. The proteinconfinement does not allow the occurrence of twisting motion in thetrapped C30, and we observed a very fast (less than 100 fs) and slower(∼13 ps) ICT processes. We believe that the reported findingsbring new knowledge for a better understanding of the photobehaviorof coumarins in solution and trapped within hydrophobic pockets. Theresults can be applied to design better coumarin-based fluorescentlabels for biological applications. [ABSTRACT FROM AUTHOR]