Molecular Origins of Optoelectronic Properties in Coumarin Dyes: Toward Designer Solar Cell and Laser Applications

Abstract

Coumarin derivatives are used in a wide range of applications, such as dye-sensitized solar cells (DSCs) and dye lasers, and have therefore attracted considerable research interest. In order to understand the molecular origins of their optoelectronic properties, molecular structures for 29 coumarin laser dyes are statistically analyzed. To this end, data for 25 compounds were taken from the Cambridge Structural Database and compared with data for four new crystal structures of coumarin laser dyes [Coumarin 487 (C(19)H(23)NO(2)), Coumarin 498 (C(16)H(17)NO(4)S), Coumarin 510 (C(20)H(18)N(2)O(2)), and Coumarin 525 (C(22)H(18)N(2)O(3))], which are reported herein. The competing contributions of different resonance states to the bond lengths of the 4- and 7-substituted coumarin laser dyes are computed based on the harmonic oscillator stabilization energy model. Consequently, a positive correlation between the contribution of the para-quinoidal resonance state and the UV-vis peak absorption wavelength of these coumarins is revealed. Furthermore, the perturbations of optoelectronic properties, owing to chemical substituents in these coumarin laser dyes, are analyzed: it is found that their UV-vis peak absorption and lasing wavelengths experience a red shift, as the electron-donating strength of the 7-position substituent increases and/or the electron-withdrawing strength of the 3- or 4-position substituent rises; this conclusion is corroborated by quantum-chemical calculations. It is also revealed that the closer the relevant substituents align with the direction of the intramolecular charge transfer (ICT), the larger the spectral shifts and the higher the molar extinction coefficients of coumarin laser dyes. These findings are important for understanding the ICT mechanism in coumarins. Meanwhile, all structure-property correlations revealed herein will enable knowledge-based molecular design of coumarins for dye lasers and DSC applications.

Molecular Design of UV–vis Absorption and Emission Properties in Organic Fluorophores: Toward Larger Bathochromic Shifts, Enhanced Molar Extinction Coefficients, and Greater Stokes Shifts

“…This strategy can effectively adjust the "push−pull" effect and shift the UV−vis spectra of coumarins, by simply changing substituents according to their varying electrondonating or -withdrawing power. 45,46 Henceforth, we also define coumarins with Ring 2 substituents at the 3-position as the set {3-sub}; similarly, {4-sub} represents coumarins with substituents at the 4-position.…”

“…46,47 However, in those studies, the {3-sub} and {4-sub} coumarins carry different chemical substituents. To gain a deeper understanding of the substituent positional effect, a natural option is to use the same substituent but attach it at different positions in the coumarin framework and then compare the optoelectronic properties of the resulting compounds.…”

Development of Green/Red-Absorbing Chromophores Based on a Coumarin Scaffold That Are Useful as Caging Groups

“…The dependence of the absorption and emission characteristics of 7-dialkylaminocoumarins with solvent polarity is usually attributed to the strong intramolecular charge transfer character (ICT) of their excited states. 19 Such negative solvatochromism was particularly dramatic in the case of the dinitro and trinitro-containing compounds (Table 1). For example, the maximum absorption of 7 was shifted from 607 nm (DCM) to 567 nm (MeOH) with increasing solvent polarity.…”

Greener One-pot Synthesis of Chromeno Oxazin and Oxazin Quinoline Derivatives and their Antibacterial Activity

“…Coumarins acts as urease inhibitors [10], corrosion inhibitors [11], optical brighteners [12], dispersed fluorescent and laser dyes [13] used in Dye Sensitized Solar Cells (DSSCs) [14][15][16][17][18][19][20][21]. The main importance lies in the functionally substituted chromenes in the field of medicinal chemistry [22][23] as natural fruit and plant extract in Ammi Visnaga as visnadine [25] and in Phlojodicarpus sibiricus as Khellactone [26].…”