Synthesis and Ultrafast Dynamics of a Donor–Acceptor–Donor Molecule Having Optoelectronic Properties

Abstract

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, anathracene as acceptor, and thiophene as spacer have been synthesized and characterized. A detailed step-wise 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 timeresolved fluorescence studies showed fluorescence quenching of anthracence moiety upon addition of thiophene while highly efficient fluorescence quenching of anthracene moiety was observed on addition of carbazole derivatives. Femtosecond transient absorption studiesconfirmed 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, k CS , was found to be very high for all the three molecules and it was on the order of 10 10 -10 11 s -1 while, the rate of charge recombination, k CR , was observed to be much slower and it was on the order of 10 8 -10 9 s -1 . The step-wise structure-property relationship leading to the efficient

Color-Tunable Delayed Fluorescence and Efficient Spin–Orbit Charge Transfer Intersystem Crossing in Compact Carbazole-Anthracene-Bodipy Triads Employing the Sequential Electron Transfer Approach

“…The evolution is quite similar also in the case of BDP-AN-N-CZ , with the only difference that the positive bands are comparatively less intense and that both the change in sign in the 530–550 nm region and the the development of the broad band at 640 nm occur on a slower timescale of 4.8 ps. The previous literature indicated that the CZ cation has an absorption band centered at around 540 nm, which in our sample could be covered due to superposition with the bleaching signal of the BDP. However, the increase in intensity in the 530–550 nm region could well signal the formation of CZ · + .…”

Spin–Orbit Charge Recombination Intersystem Crossing in Phenothiazine–Anthracene Compact Dyads: Effect of Molecular Conformation on Electronic Coupling, Electronic Transitions, and Electron Spin Polarizations of the Triplet States

“…87−90 An absorption band around 650 nm has been previously assigned to An anion, 91 as well as a peak in the 435−450 nm region. 88,89 The 650 nm band is, however, also observed for the singlet excited state spectrum of An, while the band at around 435−450 nm is in the same region of the absorption of the An triplet state. In any case, the clear observation of the PTZ cation band at 500 nm indicates the CS in the dyad.…”

“…On the basis of the previous reports, the 500 nm band can be assigned to the absorption of the PTZ cation (approx. 510 nm), while the assignment of the An anion band is more controversial. − An absorption band around 650 nm has been previously assigned to An anion, as well as a peak in the 435–450 nm region. , The 650 nm band is, however, also observed for the singlet excited state spectrum of An , while the band at around 435–450 nm is in the same region of the absorption of the An triplet state. In any case, the clear observation of the PTZ cation band at 500 nm indicates the CS in the dyad.…”

Effect of Molecular Structures of Donor Monomers of Polymers on Photovoltaic Properties

“…27,28 The molecular structure decides the electron excitation and separation pathway and efficiency. 29,30 Good understanding of this plays a crucial role in improving the efficiency of solar cells. 31−33 Here, the OSC performances of five polymers correlated to the ultrafast intramolecular charge splitting dynamics—namely, HXS-1 with CBZ polymerized at the 2 and 7 positions and 5,6-bis(octyloxy)benzo-2,1,3-thiadiazole (BOBT) at the 4 and 7 positions; HXS-2 and HXS-3 that contain PCBZ and BOBT, respectively; and HXS-4 and HXS-5 that coupled DCBZ with BOBT—were investigated.…”

“…Second, at the p–n domain interface, the CS state excitons overcome the Coulomb binding energy barrier and split to free charge . The separation and recombination processes of electron–hole pair are very important for OSCs. , However, of particular importance is the single-molecule structure first excited by photons. , The molecular structure decides the electron excitation and separation pathway and efficiency. , Good understanding of this plays a crucial role in improving the efficiency of solar cells. − Here, the OSC performances of five polymers correlated to the ultrafast intramolecular charge splitting dynamicsnamely, HXS-1 with CBZ polymerized at the 2 and 7 positions and 5,6-bis­(octyloxy)­benzo-2,1,3-thiadiazole (BOBT) at the 4 and 7 positions; HXS-2 and HXS-3 that contain PCBZ and BOBT, respectively; and HXS-4 and HXS-5 that coupled DCBZ with BOBTwere investigated.…”