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 Title: Nonadiabatic Photo-process Involving The Πσ* State In Intramolecular Charge Transfer: A Concerted Spectroscopic And Computational Study On 4-(dimethylamino)benzethyne And 4-(dimethylamino)benzonitrile. Author(s): Fujiwara, Takashige Contributor(s): Coto, Pedro B.; Segarra-Martí, Javier Subject(s): Theory and Computation Abstract: The ubiquitous nature of the low-lying $\pi\sigma$* state in the photo-excited aromatic molecules or biomolecules is widely recognized to play an important role in nonadiabatic photo-process such as photodissociation or intramolecular charge transfer (ICT). For instance, the O--H elimination channel in phenol is attributed to the state-cross of the repulsive $\pi\sigma$* state that exhibits a conical intersection with the lowest bright $\pi\pi$* state and with the ground state, leading to ultrafast electronic deactivation. A similar decay pathway has been found in the ICT formation of 4-(dialkylamino)benzonitriles in a polar environment, where an initially photoexcited Frank-Condon state bifurcates in the presence of a dark intermediate $\pi\sigma$* state that crosses the fluorescent $\pi\pi$* state, followed by a conical intersection with the twisted intramolecular charge transfer (TICT) state. We proposed such a two-fold decay mechanism that $\pi\sigma$*-state highly mediates intramolecular charge transfer in 4-(dialkylamino)benzonitriles, which is supported from both our high-level {\it ab initio} calculations and ultrafast laser spectroscopies in the previous study. 4-(Dimethylamino)benzethyne (DMABE) is isoelectronic with 4-(dimethylamino)benzonitrile (DMABN), and the electronic structures and electronic spectra of the two molecules bear very close resemblance. However, DMABN does show the ICT formation in a polar environment, whereas DMABE does not. To probe the photophysical differences among the low-lying excited-state configurations, we performed concerted time-resolved laser spectroscopies and high level {\it ab initio} multireference perturbation theory quantum-chemical (CASPT2//CASSCF) computations on the two molecules. In this paper we demonstrate the importance of the bound excited-state of a $\pi\sigma$* configuration that induce highly $\pi\sigma$*-state mediated intramolecular charge transfer in 4-(dialkylamino)benzonitriles. Issue Date: 2014-06-20 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Fujiwara, T.; Coto, P.B.; Segarra-Martí, J. NONADIABATIC PHOTO-PROCESS INVOLVING THE πσ* STATE IN INTRAMOLECULAR CHARGE TRANSFER: A CONCERTED SPECTROSCOPIC AND COMPUTATIONAL STUDY ON 4-(DIMETHYLAMINO)BENZETHYNE AND 4-(DIMETHYLAMINO)BENZONITRILE.. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.FC09 Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/51211 DOI: https://doi.org/10.15278/isms.2014.FC09 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-09-172015-04-14
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