Absorption and Fluorescence Emission Spectrum of Pyrene and Understanding the Jablonski Diagram

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1. Jablonski Diagram

Jablonski diagram에서 가장 낮은 굵은 수평선은 일반적으로 단일 상태인 분자의 바닥상태 에너지를 나타내며 S0로 표시된다. 실온에서, 이 상태는 용액에서 대부분 분자의 에너지를 나타낸다. 위쪽의 굵은 선은 3개의 들뜬 전자 상태의 바닥 진동 상태에 대한 에너지 준위이다. 왼쪽의 두 선은 첫 번째 (S1) 및 두 번째 (S2)전자 단일 상태를 나타낸다. 오른쪽에 있는 것(T1)은 첫 번째 전자 삼중항 상태의 에너지를 나타낸다. 통상적으로 그러하듯이, 첫 번째 들뜬 삼중항 상태의 에너지는 대응하는 단일항 상태의 에너지 보다 낮다.
2. Absorption Spectrum of Pyrene

Pyrene의 흡광 스펙트럼에서 관찰된 주요 피크의 에너지는 5.343eV (231nm), 5.160eV (240.3nm), 4.733eV (262nm), 4.552eV (272.4nm), 4.063eV (305.2nm), 3.882eV (319.4nm), 3.702eV (335nm)이다. 이는 Pyrene 분자의 전자 전이 과정을 잘 보여준다.
3. Fluorescence Emission Spectrum of Pyrene

Pyrene의 형광 스펙트럼에서 관찰된 주요 피크의 에너지는 3.331eV (372.2nm), 3.278eV (378.2nm), 3.236eV (383.2nm), 3.158eV (392.6nm)이다. 이는 Pyrene 분자의 들뜬 상태에서 바닥 상태로의 전자 전이 과정을 보여준다.
4. Franck-Condon Principle

아래로의 전자 전이는 Franck-Condon 원리에 부합됨을 의미하는 수직 전이이고, 형광 스펙트럼은 더 낮은 전자 상태 특유의 진동 구조를 갖는다. 진동 에너지의 일부가 주위로 상실된 후에 형광 복사선이 방출되기 때문에 형광은 입사 복사선의 진동수보다 더 낮은 진동수에서 일어난다.
5. Pyrene Photophysics

Pyrene에서 전자가 들뜰 때 S0에서 S1으로 전이되지 못하는 이유는 대칭성 때문이다. 또다른 추측으로는 Pyrene의 conjugation된 구조가 영향을 주거나 전자의 수가 많아 HOMO가 높은 위치에 위치하고 있기 때문이라고 생각한다.

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1. Jablonski Diagram

The Jablonski diagram is a widely used visual representation of the electronic energy levels and transitions that occur in molecules during photophysical and photochemical processes. It provides a clear and concise way to understand the various pathways by which a molecule can absorb, emit, or dissipate energy following the absorption of a photon. The diagram illustrates the different electronic states (ground state, singlet excited states, and triplet excited states) and the various radiative and non-radiative transitions that can occur between these states, such as absorption, fluorescence, internal conversion, intersystem crossing, and phosphorescence. Understanding the Jablonski diagram is crucial for interpreting and analyzing the photophysical behavior of molecules, which is essential in fields like photochemistry, photobiology, and materials science. The diagram serves as a valuable tool for researchers and students to visualize and comprehend the complex photophysical processes that underlie many important phenomena and applications.
2. Absorption Spectrum of Pyrene

The absorption spectrum of pyrene is an important tool for understanding the photophysical properties of this polycyclic aromatic hydrocarbon. Pyrene is known for its distinctive absorption spectrum, which exhibits a series of well-defined vibronic bands in the ultraviolet and visible regions of the electromagnetic spectrum. These absorption bands are associated with the electronic transitions from the ground state (S0) to the various vibrational levels of the first and higher excited singlet states (S1, S2, etc.) of the pyrene molecule. The absorption spectrum provides valuable information about the energy levels and the electronic structure of pyrene, which is crucial for understanding its photochemical and photophysical behavior. Additionally, the absorption spectrum can be used to determine the molar extinction coefficient, which is a measure of the molecule's ability to absorb light at a particular wavelength. This information is essential for various applications, such as fluorescence spectroscopy, photochemistry, and the development of pyrene-based materials and sensors.
3. Fluorescence Emission Spectrum of Pyrene

The fluorescence emission spectrum of pyrene is a crucial tool for understanding the photophysical properties of this polycyclic aromatic hydrocarbon. When pyrene is excited by light, it can undergo a radiative transition from the first excited singlet state (S1) to the ground state (S0), emitting a photon in the process. The resulting fluorescence emission spectrum of pyrene is characterized by a series of well-resolved vibronic bands, reflecting the various vibrational levels within the S1 state. The position, intensity, and shape of these emission bands provide valuable information about the electronic structure and energy levels of the pyrene molecule. Additionally, the fluorescence emission spectrum can be influenced by factors such as solvent polarity, temperature, and the presence of other molecules or ions, making it a useful tool for studying the microenvironment and interactions of pyrene in various systems. The fluorescence emission spectrum of pyrene has found widespread applications in fields like analytical chemistry, materials science, and biological imaging, where it is used for quantitative and qualitative analysis, as well as for probing the local environment and dynamics of pyrene-labeled molecules or materials.
4. Franck-Condon Principle

The Franck-Condon principle is a fundamental concept in quantum mechanics that explains the intensity distribution of vibronic transitions in the absorption and emission spectra of molecules. This principle states that electronic transitions occur much faster than the rearrangement of atomic nuclei, which means that the nuclear configuration of a molecule remains essentially unchanged during an electronic transition. As a result, the most intense vibronic transitions in the absorption and emission spectra correspond to those where the vibrational wavefunctions of the initial and final electronic states have the greatest overlap. The Franck-Condon principle is crucial for understanding and interpreting the photophysical behavior of molecules, as it provides a framework for predicting and explaining the observed spectral patterns, including the relative intensities of the vibronic bands. This principle has wide-ranging applications in various fields, such as photochemistry, spectroscopy, and the design of optoelectronic materials, where a deep understanding of the electronic and vibrational structure of molecules is essential for optimizing their performance and functionality.
5. Pyrene Photophysics

The photophysics of pyrene, a polycyclic aromatic hydrocarbon, is a fascinating and well-studied topic in the field of molecular spectroscopy and photochemistry. Pyrene exhibits a rich and complex photophysical behavior, which has made it a widely used model compound for investigating various photophysical processes. Upon absorption of light, pyrene can undergo a variety of electronic transitions and relaxation pathways, including fluorescence, internal conversion, intersystem crossing, and phosphorescence. The Jablonski diagram provides a clear visual representation of these processes, highlighting the different electronic states and the various radiative and non-radiative transitions that can occur. The absorption and fluorescence emission spectra of pyrene are characterized by well-resolved vibronic bands, which can be understood in terms of the Franck-Condon principle. Additionally, the photophysical behavior of pyrene can be influenced by factors such as solvent polarity, temperature, and the presence of other molecules or ions, making it a versatile tool for probing the local environment and dynamics of various systems. The study of pyrene photophysics has contributed significantly to our understanding of the fundamental principles governing the interaction of light with organic molecules, and has found numerous applications in fields such as analytical chemistry, materials science, and biological imaging.