Dissertation
Dissertation > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Theory of organic chemistry,physical organic chemistry > Organic Chemistry Structure Theory

Intramolecular Charge Transfer and Proton Transfer in Benzanilide Derivatives

Author ZhangZuo
Tutor JiangYunBao
School Xiamen University
Course Analytical Chemistry
Keywords Intramolecular charge transfer and proton transfer substituente effect solvent effect benzanilides molecular recognition fluorescent sensing
CLC O621.13
Type PhD thesis
Year 2003
Downloads 417
Quotes 2
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The abnormal emission behavior of benzanilide (BA) was first reported by O’Conell et al. in the early 1970’s and has become a subject of intense interest in the past few decades. A proton transfer (PT) model was first proposed by Kasha and co-workers, in which the abnormally long wavelength emission of BA was assigned to the PT state formed from the tautomerization within hydrogen-bonded dimer. This PT model was immediately revised due to a subsequent observation of similar Stokes-shifted long-wavelength fluorescence from N-methylbenzanilide (MBA) in which the PT channel was blocked. The long-wavelength emission of MBA was suggested to originate from the intramolecular charge transfer (CT) State, while that of BA was then ascribed to the overlapped emission from the PT and CT states. Meanwhile, Azumaya et al. proposed the twisted intramolecular charge transfer (TICT) model to account for the long-wavelength emission from both BA and MBA that twisting occurred at the amide C-N bond between anilinomoiety, the electron donor, and benzoyl moiety the electron acceptor. These two models have been supported and actively debated by several sets of research results. Discrepancies, however, still exist on the assignment of the long-wavelength emission of BA. The original proposal of the CT origin of the long-wavelength emission with BA and MBA was based mainly on an analogy to the assignment made with the well-known dual fluorescent p-dimethylaminobenzonitri1e (DMABN), and was supported by a moderate solvatochromic shift observed with MBA long-wavelength emission. It should be pointed out, however, that care needs to be taken in using this solvatochromic method that has been routinely employed for identifying the CT character of the emissive state, since with MBA and BA the number of the solvents that can be used was very limited. For BA and MBA only solvents within polarity range of n-hexane to tetrahydrofuran (THF) could be used, in more polar solvents the long-wavelength emissionwas completely quenched. Meanwhile the photo-instability of BA and MBA made it difficult to abstract credible messages from time-resolved fluorescence investigations. It therefore seems necessary to find alternative methodologies to bring about new and direct evidences for understanding the origin of the long-wave length emission observed with BA.We attempted such an alternative method by systematic variations of the redox properties of the electron donor/acceptor via introducing substituent at the electron donor (aniline moiety) and/or acceptor (benzoyl moiety). This was based on the well-known linear correlation of the exciplex energy, ECT, with the redox potentials of the electron donor (D) and acceptor (A) by the Weller equation and the modified form after introducing (0,0)-transition energy, E0.0, and ground-state repulsion energy, δErep, that directly correlated the CT emission energy, hvmax (CT), with the redox potentials. This provided an alternative way of identifying the CT character of the emissive state by directly correlating the emission energy with the redox potentials of the electron donor/acceptor within the investigated fluorophores.Systematical investigations on intramolecular charge transfer (CT) and proton transfer (PT) of benzanilide (BA) derivatives with substituents at both electron donor and acceptor moieties were carried out and their potential applications in molecular recognition and fluorescent sensing were preliminary investigated. Direct evidence for the CT nature of long-wavelength fluorescence emissive state of BAs was presented for the first time. The contents of the thesis are described in three parts.Part 1 consists of two chapters. Basic ICT photophysics of DMABN, a prototype ICT molecule, and progresses of molecular recognition and fluorescent sensing based on the ICT mechanism were briefly described in Chapter I. Recent progresses on the photophysics of BAs were reviewed in Chapter 2. The research proposals to be carried out were outlined in

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