NIR Absorption of Perylene Dyes and Fluorescence with Large Stokes' Shift by Simple Deprotonation

Chromophores [1] with light absorption at long wavelengths in the visible or even in the near infrared are becoming increasingly attractive [2]. Commonly, such a bathochromic absorption is realized with very large π systems; see for example ref. [3]. Bathochromically absorbing smaller molecules are more difficult to obtain [4], but can be developed by balancing substituent effects in conjugated π systems; compare ref. [5] and refs. therein. The majority of dyes, such as the well-known triphenylmethane dyes consist of a central acceptor (Ac.) surrounded by π systems substituted with two donor groups (Do.) according to (1). The length of the π system and the donor and acceptor abilities determine the light absorption.