Excited‐State Intramolecular Charge‐Transfer Dynamics in 4‐Dimethylamino‐4′‐cyanodiphenylacetylene: An Ultrafast Raman Loss Spectroscopic Perspective

Abstract

Photo-initiated intramolecular charge transfer (ICT) processes play a pivotal role in the excited state reaction dynamics in donor-bridge-acceptor systems. The efficacy of such a process can be improved by modifying the extent of π-conjugation, relative orientation/twists of the donor/acceptor entities and polarity of the environment. Herein, 4-dimethylamino-4'-cyanodiphenylacetylene (DACN-DPA), a typical donor-π-bridge-acceptor system, was chosen to unravel the role of various internal coordinates that govern the extent of photo-initiated ICT dynamics. Transient absorption (TA) spectra of DACN-DPA in n-hexane exhibit a lifetime of > 2 ns indicating the formation of a triplet state while, in acetonitrile, a short time-constant of ~2 ps indicates the formation of charge transferred species. Ultrafast Raman loss spectroscopy (URLS) measurements show distinct temporal and spectral dynamics of Raman bands associated with C�C and C=C stretching vibrations. The appearance of a new band at ~1492 cm À 1 in acetonitrile clearly indicates structural modification during the ultrafast ICT process. Furthermore, these observations are supported by TD-DFT computations.

Aryl sulfonate anion stabilized aromatic triangular cation [Pd3]+: syntheses, structures and properties

“…36 Basically, the excited states possessed greater polarity and was more benecial from increasing solvent polarity. [38][39][40] Generally, complex 7 conformed to the rule of uorescence intensity enhancement with increasing solvent polarity and presented apparently stronger emission in CH 3 OH. Meanwhile, the uorescence wavelengths also presented red shi when the polarity of organic solvents were increased.…”

Solvent Polarity Governs Ultrafast Structural Dynamics: A Case Study of 4-Dimethylamino-4′-carbomethoxydiphenylacetylene

“…Diphenylacetylene (DPA) is the basic unit of higher-order oligo phenylene ethynylenes and oligoynes, which are straight chains of sp hybridized carbon atoms used in molecular electronics and 1D-molecular wires. , Biswas and co-workers reported early studies on charge transfer processes in such molecules. Both D-π-A compounds − and related quadrupolar D-π-A systems and D-π-D/A-π-A systems , have potential applications as Raman and fluorimetric probes for selective sensing of biomolecules. − Recently, a planar ICT structure for 4-dimethylamino-4′-cynaodiphenylacetylene was proposed based on transient Raman spectroscopy …”

“…54−56 Recently, a planar ICT structure for 4-dimethylamino-4′-cynaodiphenylacetylene was proposed based on transient Raman spectroscopy. 57 We present herein a study of the charge transfer dynamics in 4-dimethylamino-4′-carbomethoxydiphenylacetylene (DACM-DPA) in the polar solvents (acetonitrile (MeCN) and methanol (MeOH)) and nonpolar solvent (n-hexane) based on the intricate structural dynamics that are associated with the ICT process. DACM-DPA possesses NMe 2 as the donor, CO 2 Me as the acceptor, and diphenylacetylene as the π-bridge.…”

A narrow-bandgap non-fullerene acceptor constructed with an S,N-heteroacene up to a dodecamer in size

“…Moreover, the multi-level electron pushpull effect in such a unique architecture may also bring forth facilitated exciton/charge dynamics. 23 In this regard, in the current work, two exotic NFAs, denoted as JX1 and JX2, have been effectively developed (Fig. 1a), and designed to include, respectively, decameric and dodecameric S,N-heteroacenes.…”

“…Moreover, the multi-level electron push–pull effect in such a unique architecture may also bring forth facilitated exciton/charge dynamics. 23…”