  Carriers of diffuse interstellar bands (DIBs) still need to be identified. In
a recent paper, we reported a correlation between the DIB wavelength and the
apparent UV resilience (or boost) of their carriers. We proposed that this
might be an indication of the important role of conjugated elongated molecules
among the DIB carriers. The aim of this paper is to further understand the
origin of this correlation. The analysis of 509 optical DIBs on the lines of
sight of HD 183143 and/or HD 204827 reported in the literature shows that this
correlation mainly implies the 386 narrow DIBs with a band width < 1.1 A, which
include most of the identified DIBs of the C2 and zeta families, while the
majority of the 123 broader DIBs, including the identified sigma DIBs, do not
display such a correlation. We present a possible origin of this correlation
from very strong bands of large conjugated elongated molecules, such as carbon
chains, polyacenes, or other catacondensed polycyclic aromatic hydrocarbons.
The total amount of carbon contained in all the carriers of these narrow DIBs
is a very small fraction of the interstellar carbon if their oscillator
strengths are <~1. The amount of carbon locked in the carriers of the broader
DIBs is higher, especially if their oscillator strengths are significantly
weaker.
