Self-assembly and photoinduced electron transfer in a donor- β-cyclodextrin-acceptor supramolecular system

• Published in: Journal of chemical sciences (Bangalore, India) Vol. 130; no. 10; pp. 1 - 14
• Main Authors: Krishnan, Retheesh, Krishnan, Sumesh Babu, Balan, Bijitha, Gopidas, Karical Raman
• Format: Journal Article
• Language: English
• Published: New Delhi Springer India 01-10-2018; Springer Nature B.V
• Subjects: Binding; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Cyclodextrins; Diimide; Electron transfer; Electrons; Flash photolysis; Fluorescence; Regular Article; Self-assembly; Ternary systems; donor–acceptor systems; supramolecular assembly; inclusion binding; Cyclodextrins; PET
• ISSN: 0974-3626; 0973-7103
• DOI: 10.1007/s12039-018-1535-z

Equimolar amounts of native
β
-cyclodextrin (
β
-
CD
), pyrene-linked adamantane (
PYAD
) and
tert
-butylpyromellitic diimide (
PMDI
) when dissolved in water self-assembled to form the supramolecular donor-acceptor system
PYAD
⊐
β
-
CD
≻
PMDI
. The high affinity of adamantane derivatives for inclusion binding in the
β
-
CD
cavity and the propensity of PMDI to undergo rim-binding at the narrow rim of
β
-CD led to the formation of
PYAD
⊐
β
-
CD
≻
PMDI
. The ternary complex
PYAD
⊐
β
-
CD
≻
PMDI
was thoroughly characterized using various spectroscopic techniques.
β
-CD performs three functions in the self-assembled complex: (1) encapsulate the adamantane unit and keep the pyrene (
PY
) moiety above the secondary rim, (2) rim-bind PMDI and keep it at the primary rim, and (3) act as a spacer between pyrene and PMDI. Thus, the ternary complex can function as a donor-spacer-acceptor system capable of undergoing photoinduced electron transfer (PET). Upon excitation of the pyrene moiety in
PYAD
⊐
β
-
CD
≻
PMDI
an electron is transferred from the excited pyrene to the PMDI ground state. Steady state and time resolved fluorescence experiments were carried out to study the PET in
PYAD
⊐
β
-
CD
≻
PMDI
. Existence of the ternary system and PET processes taking place within it are further supported by laser flash photolysis experiments.
Graphical abstract
β
-CD assembles donor pyrene through inclusion binding and acceptor pyromellitic diimide through rim-binding. Fluorescence intensity and lifetime quenching suggested photoinduced electron transfer from pyrene to pyromellitic diimide.