Photophysics of Two Indole-Based Cyan Fluorophores

Yu Yuan; Jingsong Liu; Ran-Ran Feng; Wenkai Zhang; Feng Gai

doi:10.1021/acs.jpcb.3c01739

Photophysics of Two Indole-Based Cyan Fluorophores

J Phys Chem B. 2023 May 25;127(20):4508-4513. doi: 10.1021/acs.jpcb.3c01739. Epub 2023 May 12.

Authors

Yu Yuan¹, Jingsong Liu², Ran-Ran Feng¹, Wenkai Zhang², Feng Gai¹

Affiliations

¹ Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
² Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, China.

PMID: 37171997
DOI: 10.1021/acs.jpcb.3c01739

Abstract

For the purpose of searching for new biological fluorophore, we assess the photophysical properties of two indole derivatives, 4-cyano-7-azaindole (4CN7AI) and 1-methyl-4-cyano-7-azaindole (1M4CN7AI), in a series of solvents. We find that (1) the absorption spectra of both derivatives are insensitive to solvents and are red-shifted from that of indole, having a maximum absorption wavelength of ca. 318 nm and a broad profile that extends beyond 370 nm; (2) both derivatives emit in the blue to green spectral range with a large Stokes shift, for example, in H₂O, the maximum emission wavelength of 4CN7AI (1M4CN7AI) is at ca. 455 nm (470 nm); (3) 4CN7AI has a higher fluorescence quantum yield (QY) and a longer fluorescence lifetime (τ_F) in aprotic solvents than in protic solvents, for example, QY (τ_F) = 0.72 ± 0.04 (7.6 ± 0.8 ns) in tetrahydrofuran and QY (τ_F) = 0.29 ± 0.03 (6.2 ± 0.6 ns) in H₂O; (4) in all of the solvents used except H₂O, the fluorescence QY (τ_F) of 1M4CN7AI is equal to or higher (longer) than 0.69 ± 0.03 (11.2 ± 0.7 ns). Taken together, these results suggest that the corresponding non-natural amino acids, 4-cyano-7-azatryptophan and 1-methyl-4-cyano-7-azatryptophan, could be useful as biological fluorophores.