Revealing the Dynamic of Excited State Proton Transfer of a π-Conjugated Salicylidene Compound: An Experimental and Theoretical Study

Abstract

Excited state intramolecular proton transfer (ESIPT) in a novel salicylidene sal-3,4-benzophen chromophore is studied by white-light femtosecond pump−probe and time-resolved fluorescence techniques, as well as by theoretical calculations under the time dependent density functional theory framework. We show that when the sal-3,4-benzophen chromophore (in enol form) is excited (at 390 nm) to the cisenol* form, it is quickly converted to the hot cis-keto* (hK*) form due to the fast ESIPT process (τ ESIPT = 150 fs). Subsequently, cooling from the hot cis-keto* (hK*) to cold cisketo* (cK*) state takes place with a characteristic time constant of ∼600 fs, with following relaxation decay time of 37 ps related with the photodynamic from sal-3,4-benzophen due to the occurrence of the cis → trans photoisomerization and intersystem crossing mechanisms. Finally, we observed the fluorescence emission from the cis-keto* at 575 nm. The dynamics of the optical process was modeled using rate equations with the proper energy level diagram and supported by theoretical calculations.

The Balance between Charge Mobility and Efficiency in All-Solution-Processed Organic Light-Emitting Diodes of Zn(II) Coordination Compounds/PFO Composites

“…Theoretical predictions of vertical excitation energies and natural transition orbitals (NTOs) for all Zn­(II) compounds were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at the PBE0/6–311++G­(d,p) level. The structures obtained by single-crystal X-ray diffraction from the ligand crystals were used for the initial structure optimization of the aquo Zn­(II) coordination compounds. ,, Solvent effects were included through the polarizable continuum method (PCM), using PFO parameters ( n PFO = 1.725 and ε PFO = 3) . All calculations were performed using the Gaussian 09 software suite…”

Modern Theoretical Approaches to Modeling the Excited-State Intramolecular Proton Transfer: An Overview

“…Afterward, an analysis of ES relaxed properties is conducted, and the barrierless/barrier-restricted character of ESIPT is determined by excited-state geometry optimization of the relevant isomers, along with predictions for the energy and intensity of the Stokes-shifted fluorescence [ 38 , 46 ]. In the final step, adiabatic potential energy profiles (PEPs) [ 47 , 48 ] or PESs [ 3 , 33 ] may be calculated, if one or multiple reaction coordinates, respectively, need to be explicitly considered. In certain cases, the energy profiles of linearly interpolated reaction paths might also efficiently support the static ESIPT analysis [ 49 ].…”

“…The second widely applied family of electronic structure methods for ESIPT investigations is time-dependent density functional theory (TD-DFT [ 70 ]), in its original design and within the Tamm–Dancoff approximation (TDA-DFT [ 71 ]). Abundant ESIPT studies at this level of theory [ 33 , 40 , 46 , 48 , 72 , 73 ] take advantage of the favorable scaling of DFT with the system size. At the same time, due to known difficulties of TD-DFT with the description of charge-transfer states, and more recent findings on its troubles with the proper determination of state orders in inverted singlet/triplet systems [ 74 , 75 ], the choice of the exchange-correlation functional and method validation usually need to be carefully conducted before meaningful conclusions can be formulated [ 36 , 59 , 76 ].…”

“…In this case, again one needs to make a compromise between the computational cost and desired accuracy. Most common recent choices in ESIPT studies seem to be favoring the cc-pVTZ [ 91 ] basis set from the Dunning family on the one hand [ 3 , 33 , 39 , 40 , 48 ], and different variants of the Pople 6-311 G(d,p) [ 92 ] basis set, on the other [ 36 , 72 , 73 ]. The latter direction finds its support in a general study by Laurent et al [ 93 ], in which the basis-set effect on vertical excitation energy calculations was investigated.…”

“…Thus far, several different approaches have been employed to tackle environmental effects on ESIPT, including microsolvation [ 43 , 69 ], the conductor-like screening model (COSMO) [ 48 , 94 , 95 ], the polarizable continuum model (PCM) [ 76 , 96 , 97 ], the solvent model density (SMD) method [ 46 , 98 ], and the integral equation formalism version of PCM (IEFPCM) [ 99 , 100 , 101 ]. The latter approach, particularly popular recently [ 33 , 37 , 73 , 102 ], has been applied e.g.…”