Broadening the Horizon of the Bell–Evans–Polanyi Principle towards Optically Triggered Structure Planarization

Abstract

Finding arelationship between kinetics and thermodynamics maybedifficult. However,semi-empirical rules exist to compensate for this shortcoming,a mong which the Bell-Evans-Polanyi (B-E-P)p rinciple is an example for reactions involving bond breakage and reformation. We expand the BE -P principle to an ew territory by probing photoinduced structure planarization (PISP) of as eries of dibenz-[b,f]azepine derivatives incorporating bent-to-planar and rotation motion. The latter involves twisting of the partial double bond character,t hereby inducing ab arrier that is substituent dependent at the para N-phenyl position. The transition-state structure and frequency data satisfy and broaden the BE -P principle to PISP reactions without bond rearrangement. Together with dual emissions during PISP,this makes possible harnessing of the kinetics/thermodynamics relationship and hence ratiometric luminescence properties for excited-state structural transformations.

Azepine‐ or Azocine‐Embedded Hexabenzocoronene Derivatives as Nitrogen‐Doped Saddle or Saddle‐Helix Nanographenes

“…Meanwhile the antiaromaticity of azepine ring was experimentally detectable. The chemical shift of the N‐methyl group in NG 1 (3.0 in D 6 C 6 ; 3.3 in CDCl 3 ) shift upfield compared it in compound 6 (3.4 in CDCl 3 ) or MDBA, [23] which suggesting the paramagnetic current environment of the azepine ring caused by antiaromaticity in compound 1 . Correspondingly, the chemical shifts of methyl groups connected to benzenes in NG 1 downfield shift after cycloaddition (from 2.1 in 6 to 2.8 in 1 in CDCl 3 ) due to higher aromaticity caused by π‐expansion (Figure S18, S20 and S21).…”

“…For the 5-methyl azepine (ring B), the two NÀC bonds are 1.42 and 1.41 , shorter than the corresponding CÀN bonds in MDBA by 0.02 and bonds of C35-C26 and C21-C22 are 0.01 longer than the corresponding bonds in MDBA. [23] Notably, with the azepine fused to the HBC ring system, the bond C35-C21 is stretched from 1.32 in MDBA to 1.43 in 1. Meanwhile, the two NÀC bonds are also 0.7-0.8 shorter than the corresponding CÀC bonds in heptagon ring in the hydrocarbon analogue.…”

Azepine‐ or Azocine‐Embedded Hexabenzocoronene Derivatives as Nitrogen‐Doped Saddle or Saddle‐Helix Nanographenes

“…Meanwhile the antiaromaticity of azepine ring was experimentally detectable. The chemical shift of the N-methyl group in NG 1 (3.0 in D 6 C 6 ; 3.3 in CDCl 3 ) shift upfield compared it in compound 6 (3.4 in CDCl 3 ) or MDBA, [23] which suggesting the paramagnetic current environment of the azepine ring caused by antiaromaticity in compound 1. Correspondingly, the chemical shifts of methyl groups connected to benzenes in NG 1 downfield shift after cycloaddition (from 2.1 in 6 to 2.8 in 1 in CDCl 3 ) due to higher aromaticity caused by p-expansion (Figure S18, S20 and S21).…”

Correlation between Kinetics and Thermodynamics for Excited-State Intramolecular Proton Transfer Reactions

“…72,73 This can be ascribed to the substitution effect that changes the forward and backward reaction rate in the same manner. 74 To date, the BEP principle has been applied in a number of chemical reactions such as those involving hydrogen atom transfer (HAT) reactions, 75−77 radical reactions, 78,79 excited-state planarization processes, 64,80 and so on. However, comprehensive analyses of the relationship between ΔE a and ΔE T*−N* for ESIPT reaction are rather scarce.…”

“…From chemical principle, the relationship for intrinsic reaction barrier versus energy difference elaborated above leads us to mull the classical mechanistic approaches to access the kinetics–thermodynamics relationship of ESIPT, among which the Bell–Evans–Polanyi (BEP) principle, a long-standing semiempirical approach, ,− has received our attention. Considering ESIPT as a classical A–H bond breakage–reformation reaction, such as A–H + B → A + H–B, the BEP principle states that if the geometries and the curvature of PES at transition states are approximately the same along the reaction coordinate within a family of molecules, there is a linear relation between activation energy (Δ E a ) and Δ E T*–N* in the case of ESIPT, expressed as where the intercept Δ E 0 represents the referential activation energy for a family of derivatives when Δ E T*–N* = 0. α represents the character of the position of the transition state along the reaction coordinate, which should be in a range of 0 ≤ α ≤ 1 .…”