Facilitated Photolysis of 9-Fluorenol in Alcohols by Excited-State Hydrogen Bond Reorganization

Abstract

Time-dependent density functional theory (TDDFT) and second-order coupled cluster method with resolution-of-the-identity approximation (RICC2) were used to investigate the photolysis dynamics of 9-fluorenol (FOH) in alcohols. In this work, a novel mechanism for the accelerated photolysis dynamics of FOH in alcohols is proposed for the first time. The two hydrogen bonds present different effects in the dissociation process of C 9 ÀO bond in MeOH Á Á Á FOH Á Á Á MeOH trimer: formation of hydrogen bond MeOH Á Á Á FOH could weaken the C 9 ÀO bond, while, hydrogen bond FOH Á Á Á MeOH fastens the bond. Moreover, the thermodynamic equilibrium can be accomplished in both ground and excited states between hydrogen-bonded complexes, since the hydrogen bond reorganization occurs in hundreds of femtosecond upon the excitation. The excited-state potential energy (PE) curves along C 9 ÀO bond have been optimized in S 1 state. The cleavage of C 9 ÀO bond upon the photoexcitation would be facilitated effectively in MeOH Á Á Á FOH dimer. This leads the thermodynamic equilibrium between hydrogen-bonded complexes leaning to the side of MeOH Á Á Á FOH dimer to quench the fluorescence. Therefore, the photolysis of 9-fluorenol in alcohols can be facilitated effectively by MeOH Á Á Á FOH hydrogen bond via excited-state hydrogen bond reorganization. Additionally, the excited-state hydrogen bond reorganization is also the rate-controlling step in photolysis of FOH in alcohols, since there is no barrier in the PE curve of MeOH Á Á Á FOH dimer.

COOPERATIVITY BETWEEN HYDROGEN BOND AND HALOGEN BOND INHBr⋯BrX⋯HBr (X = F, Cl, Br)

“…Moreover, new research methods are emerging constantly. For example, the photolysis process of 9-°u orenol in alcohols can be facilitated e®ectively by the hydrogen bond reorganization in excited state by investigating the exited-state hydrogen bonding dynamics by the time dependent density functional theory (TD-DFT)/RICC2 method, 26 the network analysis method is useful for understanding and predicting the structure and function of room temperature ionic liquids (RTILs), 27 the hydrogen-bonding changes in electronically excited states whether strengthened or weakened for the hydrogenbonded complexes play an important role on the photochemistry in solutions by studying the excited-state hydrogen bonding dynamics using TD-DFT method, 28 the substituent e®ect in 3-amino 2-iminomethyl acryl aldehyde (AIA) and its derivatives depends on the nature of substituent and on its position in the molecule, 29 the search performance of the novel molecular memetic algorithm (MOL-MA) is shown to outperform its compeers when pitted against those reported in the literature for nding transition states as well as recent advances in niching algorithms in terms of solution precision, computational e®ort and number of transition states uncovered. 30 Hydrogen bond 31À33 and halogen bond 34À41 are well-known noncovalent interactions, which have attracted much attention and a signi¯cant amount of experimental and theoretical research.…”