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The thesis entitled: ‘Synthesis and Photochemistry of a few Olefin
appended Dibenzobarrelenes and Bisdibenzobarrelenes’ is divided into 5
chapters.In Chapter 1, the fundamental concepts of Diels-Alder reaction, di-r:methane
rearrangement and energy transfer process in organic photochemistry
is discussed.Chapter 2 presents the synthesis of 9-olefin appended
anthracenes and bisanthracenes. The target of synthesising various bridgehead olefin appended
dibenzobarrelenes and some novel bisdibenzobarrelenes, led us to the
synthesis of the appropriate alkenylanthracenes and bisanthracenes as
precursor molecules. Diels-Alder reaction was the synthetic tool for the
preparation of the target olefin appended dibenzobarrelenes and
bisdibenzobarrelenes. This chapter attempts to throw light on our endeavours
in synthesising the various 9-alkenylanthracenes and bisanthracenes.Chapter 3 deals with the synthesis of olefin
appended dibenzobarrelenes and bisdibenzobarrelenes.
Ever since the discovery of di-It-methane rearrangement
dibenzobarrelenes, tailored with dijferent substituents at various positions
have always been a tool to photochemists in unravelling the mechanisms of
light induced reactions. Our intention of analysing the role of a It-moiety at
the bridgehead position of the dibenzobarrelene, was synthetically envisaged
via the Diels-Alder reaction. Bisdibenzobarrelenes were synthesised through
tandem Diels-Alder reaction. Various alkenylanthracenes and bisanthracenes
were employed as dienes and the dienophiles used were dimethyl
acetylenedicarboxylate and dibenzoylacetylene. In this chapter, we report our
venture in synthesising the various olefin appended dibenzobarrelenes and
bisdibenzobarrelenes. Chapter 4 describes
the preliminary time-resolved fluorescence studies of some olefin appended
dibenzobarrelenes and bisdibenzobarrelenes.To understand the primary and secondary physicochemical processes
in a photochemical reaction it is necessary to characterise the excited states
and the transient intermediates during their short lifetime. A number of
methods developed on the basis of the physical properties of the transient
species are available for their detection. Time-correlated single-photon
counting technique has been utilised in the present study of the excited states
of olefin appended dibenzobarrelenes and bisdibenzobarrelenes.
To understand the primary and secondary physicochemical processes
in a photochemical reaction it is necessary to characterise the excited states
and the transient intermediates during their short lifetime. A number of
methods developed on the basis of the physical properties of the transient
species are available for their detection. Time-correlated single-photon
counting technique has been utilised in the present study of the excited states
of olefin appended dibenzobarrelenes and bisdibenzobarrelenes.Chapter 5 portrays the
photochemistry of olefin appended dibenzobarrelenes and
bisdibenzobarrelenes. Dibenzocyclooctatetraene and dibenzosemibullvalene are the
photoproducts obtained respectively through the singlet excited state and the
triplet excited state of dibenzobarrelenes. Chemical literature shows
evidences of the photoreactivity of dibenzobarrelenes generating both the
singlet and triplet mediated photoproducts, in a single photoreaction. Our
research target in synthesising various bridgehead olefin appended
dibenzobarrelenes and bisdibenzobarrelenes, was based on the perception
that olefins are eflicient triplet quenchers, thereby quenching intramolecularly
the triplet excited state of the barrelenes. A It-moiety at the bridgehead
position of the dibenzobarrelene, creates a tetra tr-methane system, which
similar to a 6li—7l' or tri-tr-methane systems, could be the fertile ground for
interesting photochemical rearrangements. Our attempts in deciphering the
photochemistry of the olefin appended dibenzobarrelenes and
bisdibenzobarrelenes is the substance of this chapter. |
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