Regulation of photodynamic interactions in 1,8-naphthalimide-linker-phenothiazine dyads by cyclodextrins.

ABSTRACT

This study examines the effects of cyclodextrin (CD) on the photophysical properties of 1,8-naphthalimide (NI) derivatives including NI-linker-phenothiazine (NI-L-PTZ) dyads in a H2O/CH3CN solution (v/v = 9 1). Peculiar excimer and exciplex emissions were observed with reference NI and NI-L-PTZ, respectively, in an aqueous environment. The NI-CD complexes exhibited monomeric emission spectral features, which resulted from their inclusion into the CD cavity. The complex formation constants of CDs with the NI derivatives were determined. The T1-Tn absorption band of (3)NI* was observed at around 470 nm during nanosecond-laser flash photolysis. Photoinduced electron transfer in NI-L-PTZ led to NI˙(-) and PTZ˙(+) from the T1 state. In protic polar solvents, NI˙(-) easily formed a ketyl radical (NIH˙) by hydrogen abstraction from H2O, and showed a transient absorption band at around 400 nm. The charge recombination (CR) time of the transient species at 400 nm showed a strong CD dependency, and the CR time of the dyad in γ-CD was increased markedly compared with in ß-CD. This suggests that the PTZ moiety can also be included in the γ-CD cavity.