1 research outputs found
Synthesis and Ultrafast Dynamics of a Donor–Acceptor–Donor Molecule Having Optoelectronic Properties
The
use of push–pull molecules having donor (D) and acceptor (A)
parts arranged in different shapes are being widely studied for application
in various optoelectronic devices. In this study three covalently
linked D–A–D molecules containing three different carbazole
derivatives as donor, anthracene as acceptor, and thiophene as spacer
have been synthesized and characterized. A detailed stepwise study
has been carried out using anthracene, thiophene–anthracene,
and carbazole–thiophene–anthracene derivatives so as
to indicate the role of each moiety in the molecule. Steady state
fluorescence, time-resolved fluorescence, transient absorption, and
cyclic voltammetric methods have been employed to understand the intramolecular
charge separation (CS) and charge recombination (CR) dynamics in solvents
of different polarity. The thermodynamic free-energy obtained by measuring
the redox potential and singlet state energy suggested the possibility
of electron transfer from the excited singlet state of carbazole moiety
to the anthracene entity. Steady state and time-resolved fluorescence
studies showed fluorescence quenching of anthracene moiety upon addition
of thiophene while highly efficient fluorescence quenching of anthracene
moiety was observed on addition of carbazole derivatives. Femtosecond
transient absorption studies confirmed the electron transfer to be
the mechanism of fluorescence quenching, in which formation and recombination
dynamics of electron-transfer products, anthracene radical anion and
carbazole radical cation, were analyzed. The rate of charge separation, <i>k</i><sub>CS</sub>, was found to be very high for all the three
molecules, and it was on the order of 10<sup>10</sup>–10<sup>11</sup> s<sup>–1</sup>, while the rate of charge recombination, <i>k</i><sub>CR</sub>, was observed to be much slower, and it was
on the order of 10<sup>8</sup>–10<sup>9</sup> s<sup>–1</sup>. The stepwise structure–property relationship leading to
the efficient charge separated state established in the systems studied
would help in the improved design of optoelectronic materials that
use these moieties