Structural changes of 1-(phenylethynyl)naphthalene upon electronic excitation from Franck–Condon fits of several fluorescence emission spectra

• Published in: Journal of molecular structure 2022-02, Vol.1250, p.131910, Article 131910
• Main Authors: Hebestreit, Marie-Luise, Henrichs, Christian, Schäfer, Johannes, Martini, Jascha, Auerswald, Johannes, Fischer, Ingo, Krueger, Anke, Schmitt, Michael
• Format: Article
• Language: English
• Subjects: 1-(phenylethynyl)naphthalene; Bichromophore; Excited state; Franck–Condon analysis; Structure
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2021.131910

•Geometry changes of 1-(phenylethynyl)naphthalene upon electronic excitation were determined from fits of fluorescence emission spectra.•The lowest energy feature in the excitation spectrum is assigned to the Lb-state.•The geometry changes are compared to the results of ab initio calculations at the approximate coupled cluster singles and doubles (CC2) level of theory.•La and Lb excited states of 1-PEN are energetically nearly degenerate. [Display omitted] The structural changes of 1-(Phenylethynyl)naphthalene (1-PEN) upon excitation from the ground state to the lowest excited singlet state have been assessed from a combined Franck–Condon-Fit of fluorescence emission spectra after excitation of several vibronic bands of 1-PEN and ab initio calculations. An analysis of the infrared spectrum, the laser induced fluorescence (LIF) spectrum and the fluorescence emission spectra is given on the basis of the approximate coupled cluster singles and doubles model (CC2) within the resolution-of-identity approximation and taking spin-component scaling into account. The excited state structure of 1-PEN is found to be planar, with the major geometry changes upon excitation localized in the naphthalene moiety. Electron density shifts from the naphthyl ring to the phenyl ring upon electronic excitation, leading to an increase of the permanent dipole moment of 1-PEN. The lowest electronically excited state of 1-PEN can be labeled as 1Lb-state, with the 1La-state energetically quasi-degenerate. The geometry changes, determined from the Franck–Condon analysis are in agreement with this assignment.