Fluorosolvatochromism of monomethyl indoles: further evidence in support of a new photophysical model for the indole chromophore

In this study, we investigated whether a change exists in the emitting state of the monomethyl indoles, dissolved in 1‐chlorobutane (ClB) and 2‐methylbutane (2MB), resulting from a dipolarity increase of the solvent. Analysis of the solvatochromism of monomethyl indoles in ClB at 343–133 K and in 2MB at 293–113 K leads to the following conclusions: (i) the state S₁ is the greatest contributor to the structured emission of 4‐Me‐, 5‐Me‐, and 7‐MeIndole; (ii) lowering the temperature of solutions of these compounds in ClB or 2MB below 113 K leads not to a structureless emission or bathochromic shift typical for an S₁′ state; (iii) 1‐Me‐, 2‐Me‐, 3‐Me‐, and 6‐MeIndole exhibit a structured emission typical for an S₁ state in 2MB but show an invariably structureless emission, subject to a red shift in ClB as the temperature is lowered, which is suggestive for an S₁′ emitting state; and (iv) lowering the temperature of solutions of the previous compounds below 133 K causes their emission spreading to become structured and blueshifted (two typical features for an emission from their S₁ state). Copyright © 2015 John Wiley & Sons, Ltd.