Estimation of the first excitation energy in diradicaloid croconate dyes having absorption in the near infra red (NIR): A DFT and SF-TDDFT study

For a singlet system with a high diradical character like croconate molecule the mildly instable RB3LYP solution yields HOMO-LUMO gaps which match the experimental values unlike the more stable BS-UB3LYP which is spin contaminated.